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[[Category:Non parametric generators]]
[[Category:Stateful transactions]]
A generator is an executable entity (like a function or procedure) that contains code that yields a sequence of values, one at a time, so that each time you call the generator, the next value in the sequence is provided.
Generators are often built on top of coroutines or objects so that the internal state of the object is handled “naturally”.
Generators are often used in situations where a sequence is potentially infinite, and where it is possible to construct the next value of the sequence with only minimal state.
;Task:
* Create a function that returns a generation of the m'th powers of the positive integers starting from zero, in order, and without obvious or simple upper limit. (Any upper limit to the generator should not be stated in the source but should be down to factors such as the languages natural integer size limit or computational time/size).
* Use it to create a generator of:
:::* Squares.
:::* Cubes.
* Drop the first 20 values from this last generator of filtered results, and then show the next 10 values.
Note that this task ''requires'' the use of generators in the calculation of the result.
;Also see:
* [[wp:Generator (computer_science)|Generator]]
<br><br>
=={{header|11l}}==
{{trans|C++}}
<syntaxhighlight lang="11l">T Generator
F.virtual.abstract next() -> Float
T PowersGenerator(Generator)
i = 0.0
Float e
F (e)
.e = e
F.virtual.assign next() -> Float
V r = .i ^ .e
.i++
R r
T Filter
Generator gen, filter
Float lastG, lastF
F (Generator gen, filter)
.gen = gen
.filter = filter
.lastG = .gen.next()
.lastF = .filter.next()
F ()()
L .lastG >= .lastF
I .lastG == .lastF
.lastG = .gen.next()
.lastF = .filter.next()
V out = .lastG
.lastG = .gen.next()
R out
V gen = Filter(PowersGenerator(2), PowersGenerator(3))
L 20
gen()
L 10
print(gen(), end' ‘ ’)</syntaxhighlight>
{{out}}
<pre>
529 576 625 676 784 841 900 961 1024 1089
</pre>
=={{header|Ada}}==
Line 29 ⟶ 86:
generator.ads:
<
type Generator is tagged private;
Line 51 ⟶ 108:
end record;
end Generator;</
generator-filtered.ads:
<
type Filtered_Generator is new Generator with private;
Line 72 ⟶ 129:
end record;
end Generator.Filtered;</
generator.adb:
<
--------------
Line 136 ⟶ 193:
end Set_Generator_Function;
end Generator;</
generator-filtered.adb:
<
-----------
Line 197 ⟶ 254:
end Set_Filter;
end Generator.Filtered;</
example use:
<
with Generator.Filtered;
Line 234 ⟶ 291:
end loop;
end Generator_Test;</
{{out}}
Line 252 ⟶ 309:
{{works with|ALGOL 68G|Any - tested with release [http://sourceforge.net/projects/algol68/files/algol68g/algol68g-2.3.5 algol68g-2.3.5].}}
{{wont work with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d] - due to extensive use of '''format'''[ted] ''transput''.}}
'''File: Template.Generator.a68'''<
MODE GENVALUE = PROC(YIELDVALUE)VOID;
Line 314 ⟶ 371:
PROC powers = (VALUE m, YIELDVALUE yield)VOID:
FOR n FROM 0 DO yield(n ** m) OD;</
MODE VALUE = INT;
Line 322 ⟶ 379:
GENVALUE fil = gen filtered(squares, cubes,);
printf(($g(0)x$, get list(gen slice(fil, 20, 30, )) ))</
{{out}}
<pre>
529 576 625 676 784 841 900 961 1024 1089
</pre>
=={{header|AppleScript}}==
Composable generators can be constructed from the methods and persistent properties of ''script'' objects:
{{Trans|JavaScript}}
{{Trans|Python}}
<syntaxhighlight lang="applescript">----------------- EXPONENTIAL / GENERATOR ----------------
-- powers :: Gen [Int]
on powers(n)
script f
on |λ|(x)
x ^ n as integer
end |λ|
end script
fmapGen(f, enumFrom(0))
end powers
--------------------------- TEST -------------------------
on run
take(10, ¬
drop(20, ¬
differenceGen(powers(2), powers(3))))
--> {529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089}
end run
------------------------- GENERIC ------------------------
-- Just :: a -> Maybe a
on Just(x)
{type:"Maybe", Nothing:false, Just:x}
end Just
-- Nothing :: Maybe a
on Nothing()
{type:"Maybe", Nothing:true}
end Nothing
-- Tuple (,) :: a -> b -> (a, b)
on Tuple(a, b)
{type:"Tuple", |1|:a, |2|:b, length:2}
end Tuple
-- differenceGen :: Gen [a] -> Gen [a] -> Gen [a]
on differenceGen(ga, gb)
-- All values of ga except any
-- already seen in gb.
script
property g : zipGen(ga, gb)
property bs : {}
property xy : missing value
on |λ|()
set xy to g's |λ|()
if missing value is xy then
xy
else
set x to |1| of xy
set y to |2| of xy
set bs to {y} & bs
if bs contains x then
|λ|() -- Next in series.
else
x
end if
end if
end |λ|
end script
end differenceGen
-- drop :: Int -> [a] -> [a]
-- drop :: Int -> String -> String
on drop(n, xs)
set c to class of xs
if script is not c then
if string is not c then
if n < length of xs then
items (1 + n) thru -1 of xs
else
{}
end if
else
if n < length of xs then
text (1 + n) thru -1 of xs
else
""
end if
end if
else
take(n, xs) -- consumed
return xs
end if
end drop
-- enumFrom :: Int -> [Int]
on enumFrom(x)
script
property v : missing value
on |λ|()
if missing value is not v then
set v to 1 + v
else
set v to x
end if
return v
end |λ|
end script
end enumFrom
-- fmapGen <$> :: (a -> b) -> Gen [a] -> Gen [b]
on fmapGen(f, gen)
script
property g : mReturn(f)
on |λ|()
set v to gen's |λ|()
if v is missing value then
v
else
g's |λ|(v)
end if
end |λ|
end script
end fmapGen
-- length :: [a] -> Int
on |length|(xs)
set c to class of xs
if list is c or string is c then
length of xs
else
(2 ^ 29 - 1) -- (maxInt - simple proxy for non-finite)
end if
end |length|
-- Lift 2nd class handler function into 1st class script wrapper
-- mReturn :: First-class m => (a -> b) -> m (a -> b)
on mReturn(f)
if script is class of f then
f
else
script
property |λ| : f
end script
end if
end mReturn
-- take :: Int -> [a] -> [a]
-- take :: Int -> String -> String
on take(n, xs)
set c to class of xs
if list is c then
if 0 < n then
items 1 thru min(n, length of xs) of xs
else
{}
end if
else if string is c then
if 0 < n then
text 1 thru min(n, length of xs) of xs
else
""
end if
else if script is c then
set ys to {}
repeat with i from 1 to n
set v to xs's |λ|()
if missing value is v then
return ys
else
set end of ys to v
end if
end repeat
return ys
else
missing value
end if
end take
-- uncons :: [a] -> Maybe (a, [a])
on uncons(xs)
set lng to |length|(xs)
if 0 = lng then
Nothing()
else
if (2 ^ 29 - 1) as integer > lng then
if class of xs is string then
set cs to text items of xs
Just(Tuple(item 1 of cs, rest of cs))
else
Just(Tuple(item 1 of xs, rest of xs))
end if
else
set nxt to take(1, xs)
if {} is nxt then
Nothing()
else
Just(Tuple(item 1 of nxt, xs))
end if
end if
end if
end uncons
-- zipGen :: Gen [a] -> Gen [b] -> Gen [(a, b)]
on zipGen(ga, gb)
script
property ma : missing value
property mb : missing value
on |λ|()
if missing value is ma then
set ma to uncons(ga)
set mb to uncons(gb)
end if
if Nothing of ma or Nothing of mb then
missing value
else
set ta to Just of ma
set tb to Just of mb
set x to Tuple(|1| of ta, |1| of tb)
set ma to uncons(|2| of ta)
set mb to uncons(|2| of tb)
return x
end if
end |λ|
end script
end zipGen</syntaxhighlight>
{{Out}}
<pre>{529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089}</pre>
=={{header|ATS}}==
<syntaxhighlight lang="ats">
(* "Generators" *)
(* I implement "generators" as non-linear closures. *)
#include "share/atspre_staload.hats"
#define NIL list_nil ()
#define :: list_cons
(* Integer powers where base and power are of any unsigned integer
types. *)
fn {tk_b, tk_p : tkind}
g1uint_ipow
(base : g1uint tk_b,
power : g1uint tk_p)
:<> g1uint tk_b =
let
fun
loop {p : nat}
.<p>.
(b : g1uint tk_b,
p : g1uint (tk_p, p),
accum : g1uint tk_b)
:<> g1uint tk_b =
let
val ph = half p
val accum = (if ph + ph = p then accum else accum * b)
in
if ph = g1i2u 0 then
accum
else
loop (b * b, ph, accum)
end
prval () = lemma_g1uint_param base
prval () = lemma_g1uint_param power
in
loop (base, power, g1i2u 1)
end
overload ipow with g1uint_ipow of 100
(* Some unit tests of ipow. *)
val- 0U = ipow (0U, 100U)
val- 1U = ipow (0U, 0U) (* Sometimes a convenient result. *)
val- 9UL = ipow (3UL, 2ULL)
val- 81ULL = ipow (3ULL, 4U)
typedef generator (tk : tkind) =
() -<cloref1> g1uint tk
typedef option_generator (tk : tkind) =
() -<cloref1> Option (g1uint tk)
fn {tk_b : tkind}
{tk_p : tkind}
make_powers_generator
(power : g1uint tk_p)
:<!wrt> generator tk_b =
let
val base : ref (g1uint tk_b) = ref (g1i2u 0)
in
lam () =>
let
val b = !base
val result = ipow (b, power)
in
!base := succ b;
result
end
end
fn {tk : tkind}
make_generator_of_1_that_are_not_also_2
(gen1 : generator tk,
gen2 : generator tk)
:<!wrt> generator tk =
let
val initialized : ref bool = ref false
val x2 : ref (g1uint tk) = ref (g1i2u 0)
fn
check (x1 : g1uint tk)
:<1> bool =
let
fun
loop ()
:<1> bool =
if x1 <= !x2 then
(x1 <> !x2)
else
begin
!x2 := gen2 ();
loop ()
end
in
loop ()
end
in
lam () =>
let
var result : g1uint tk = g1i2u 0
var found_one : bool = false
in
if ~(!initialized) then
begin
!x2 := gen2 ();
!initialized := true
end;
while (~found_one)
let
val next1 = gen1 ()
in
if check next1 then
begin
result := next1;
found_one := true
end
end;
result
end
end
fn {tk : tkind}
make_dropper
(n : size_t,
gen : generator tk)
:<!wrt> generator tk =
let
val counter : ref size_t = ref n
in
lam () =>
begin
while (isneqz (!counter))
let
val _ = gen ()
in
!counter := pred (!counter)
end;
gen ()
end
end
fn {tk : tkind}
make_taker
(n : size_t,
gen : generator tk)
:<!wrt> option_generator tk =
let
val counter : ref size_t = ref n
in
lam () =>
if iseqz (!counter) then
None ()
else
begin
!counter := pred (!counter);
Some (gen ())
end
end
implement
main0 () =
let
stadef tk = uintknd
macdef filter = make_generator_of_1_that_are_not_also_2<tk>
val squares_generator = make_powers_generator<tk> 2U
val cubes_generator = make_powers_generator<tk> 3U
val gen = filter (squares_generator, cubes_generator)
val gen = make_dropper<tk> (i2sz 20, gen)
val gen = make_taker<tk> (i2sz 10, gen)
var done : bool = false
in
while (~done)
begin
case+ gen () of
| None () => done := true
| Some x => print! (" ", x)
end;
println! ()
end
</syntaxhighlight>
{{out}}
<pre>$ patscc -DATS_MEMALLOC_GCBDW generator-exponential.dats -lgc && ./a.out
529 576 625 676 784 841 900 961 1024 1089</pre>
=={{header|C}}==
Line 336 ⟶ 824:
Then the generator passes some 64-bit integer to <tt>yield64()</tt>, which switches to the first cothread, where <tt>next64()</tt> returns this 64-bit integer.
<
#include <stdlib.h> /* exit() */
#include <stdio.h> /* printf() */
Line 497 ⟶ 985:
gen.free(&gen); /* Free memory. */
return 0;
}</
One must download [http://byuu.org/programming/ libco] and give libco.c to the compiler.
Line 507 ⟶ 995:
===Using struct to store state===
<
#include <stdlib.h>
#include <math.h>
Line 580 ⟶ 1,068:
return 0;
}</
{{out}}<pre>529
576
Line 591 ⟶ 1,079:
1024
1089</pre>
=={{header|C sharp}}==
<syntaxhighlight lang="csharp">using System;
using System.Collections.Generic;
using System.Linq;
static class Program {
static void Main() {
Func<int, IEnumerable<int>> ms = m => Infinite().Select(i => (int)Math.Pow(i, m));
var squares = ms(2);
var cubes = ms(3);
var filtered = squares.Where(square => cubes.First(cube => cube >= square) != square);
var final = filtered.Skip(20).Take(10);
foreach (var i in final) Console.WriteLine(i);
}
static IEnumerable<int> Infinite() {
var i = 0;
while (true) yield return i++;
}
}</syntaxhighlight>
=={{header|C++}}==
Line 596 ⟶ 1,105:
A templated solution.
<
using namespace std;
Line 661 ⟶ 1,170:
for(int i = 20; i < 30; ++i)
cout << i << ": " << gen() << endl;
}</
{{out}}
Line 676 ⟶ 1,185:
29: 1089
</pre>
=={{header|Clojure}}==
Line 706 ⟶ 1,194:
Thus we can define squares and cubes as lazy sequences:
<
(def squares (powers 2))
(take 5 squares) ; => (1 4 9 16 25)</
The definition here of the squares-not-cubes lazy sequence uses the loop/recur construct,
which isn't lazy. So we use ''lazy-seq'' explicity:
<
([] (squares-not-cubes (powers 2) (powers 3)))
([squares cubes]
Line 723 ⟶ 1,211:
(->> (squares-not-cubes) (drop 20) (take 10))
; => (529 576 625 676 784 841 900 961 1024 1089)</
If we really need a generator function for some reason, any lazy sequence
Line 729 ⟶ 1,217:
function ''repeatedly''.)
<
(let [state (atom (cons nil sequence))]
(fn [] (first (swap! state rest)))
(def f (seq->fn (squares-not-cubes)))
[(f) (f) (f)] ; => [4 9 16]</
=={{header|Common Lisp}}==
<
(values-list (loop repeat n collect (funcall seq))))
Line 757 ⟶ 1,245:
(let ((2not3 (filter-seq (power-seq 2) (power-seq 3))))
(take 2not3 20) ;; drop 20
(princ (multiple-value-list (take 2not3 10))))</
=={{header|D}}==
===Efficient Standard Version===
<
import std.stdio, std.bigint, std.range, std.algorithm;
Line 768 ⟶ 1,256:
squares.setDifference(cubes).drop(20).take(10).writeln;
}</
{{out}}
<pre>[529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089]</pre>
Line 774 ⟶ 1,262:
===Simple Ranges-Based Implementation===
{{trans|C#}}
<
import std.stdio, std.bigint, std.range, std.algorithm;
Line 785 ⟶ 1,273:
.take(10)
.writeln;
}</
The output is the same.
===More Efficient Ranges-Based Version===
<
struct Filtered(R1, R2) if (is(ElementType!R1 == ElementType!R2)) {
Line 835 ⟶ 1,323:
auto cubes = 0.sequence!"n".map!(i => i.BigInt ^^ 3);
filtered(squares, cubes).drop(20).take(10).writeln;
}</
The output is the same.
===Closures-Based Version===
{{trans|Go}}
<
auto powers(in double e) pure nothrow {
Line 873 ⟶ 1,361:
write(fgen(), " ");
writeln;
}</
{{out}}
<pre>529 576 625 676 784 841 900 961 1024 1089 </pre>
===Generator Range Version===
<
auto powers(in uint m) pure nothrow @safe {
Line 905 ⟶ 1,393:
auto squares = 2.powers, cubes = 3.powers;
filtered(squares, cubes).drop(20).take(10).writeln;
}</
{{out}}
<pre>[529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089]</pre>
=={{header|Delphi}}==
{{works with|Delphi|6.0}}
{{libheader|SysUtils,Math,StdCtrls,ExtCtrls}}
This program demostrates hierarchial object structure. It starts with a base generator object that has all the basic features need by a generator. Child objects are then created which customized the behavior to generate squares, cubes and filtered squares. Once the base object is created, any variation can be created with just a few lines of code. This is the power of polymorphism and inheritance.
<syntaxhighlight lang="Delphi">
{Custom object forms basic generator}
type TCustomGen = class(TObject)
private
FNumber: integer;
FExponent: integer;
FStart: integer;
protected
property Exponent: integer read FExponent write FExponent;
public
constructor Create; virtual;
procedure Reset;
function Next: integer; virtual;
procedure Skip(Count: integer);
property Start: integer read FStart write FStart;
end;
{Child object specifically for generating Squares}
type TSquareGen = class(TCustomGen)
public
constructor Create; override;
end;
{Child object specifically for generating cubes}
type TCubeGen = class(TCustomGen)
public
constructor Create; override;
end;
{Child object specifically for filtering squares}
type TFilterSquareGen = class(TSquareGen)
private
function IsCube(N: integer): boolean;
public
function Next: integer; override;
end;
{ TCustomGen }
constructor TCustomGen.Create;
begin
Start:=0;
{Default to returning X^1}
Exponent:=1;
Reset;
end;
function TCustomGen.Next: integer;
{Find next number in sequence}
var I: integer;
begin
Result:=FNumber;
{Raise to specified power}
for I:=1 to FExponent-1 do Result:=Result * Result;
{Get next base}
Inc(FNumber);
end;
procedure TCustomGen.Reset;
begin
FNumber:=Start;
end;
procedure TCustomGen.Skip(Count: integer);
{Skip specified number of items}
var I: integer;
begin
for I:=1 to Count do Next;
end;
{ TSquareGen }
constructor TSquareGen.Create;
begin
inherited;
Exponent:=2;
end;
{ TCubeGen }
constructor TCubeGen.Create;
begin
inherited;
Exponent:=3;
end;
{ TFilterSquareGen }
function TFilterSquareGen.IsCube(N: integer): boolean;
{Test if number is perfect cube}
var I: integer;
begin
I:=Round(Power(N,1/3));
Result:=I*I*I = N;
end;
function TFilterSquareGen.Next: integer;
begin
{Gets inherited next square, rejects cubes}
repeat Result:=inherited Next
until not IsCube(Result);
end;
{-----------------------------------------------------------}
procedure DoTest(Memo: TMemo; Gen: TCustomGen; SkipCnt: integer; Title: string);
{Carry out TGenerators tests. "Gen" is a TCustomGen which is the parent of}
{all generators. That means "DoTest" can work with any type of generator}
var S: string;
var I,V: integer;
begin
Gen.Reset;
Gen.Skip(SkipCnt);
Memo.Lines.Add(Title);
S:='[';
for I:=1 to 10 do S:=S+Format(' %d',[Gen.Next]);
Memo.Lines.Add(S+']');
end;
procedure TestGenerators(Memo: TMemo);
{Tests all three types of generators}
var SquareGen: TSquareGen;
var CubeGen: TCubeGen;
var Filtered: TFilterSquareGen;
begin
SquareGen:=TSquareGen.Create;
try
CubeGen:=TCubeGen.Create;
try
Filtered:=TFilterSquareGen.Create;
try
DoTest(Memo,SquareGen,0,'Testing Square Generator');
DoTest(Memo,CubeGen,0,'Testing Cube Generator');
DoTest(Memo,Filtered,20,'Testing Squares with cubes removed');
finally Filtered.Free; end;
finally CubeGen.Free; end;
finally SquareGen.Free; end;
end;
</syntaxhighlight>
{{out}}
<pre>
Testing Square Generator
[ 0 1 4 9 16 25 36 49 64 81]
Testing Cube Generator
[ 0 1 16 81 256 625 1296 2401 4096 6561]
Testing Squares with cubes removed
[ 529 576 625 676 784 841 900 961 1024 1089]
</pre>
=={{header|E}}==
Line 913 ⟶ 1,572:
E does not provide coroutines on the principle that interleaving of execution of code should be explicit to avoid unexpected interactions. However, this problem does not especially require them. Each generator here is simply a function that returns the next value in the sequence when called.
<
var i := -1
return def powerGenerator() {
Line 947 ⟶ 1,606:
print(`${squaresNotCubes()} `)
}
println()</
=={{header|EchoLisp}}==
<
(lib 'tasks) ;; for make-generator
Line 987 ⟶ 1,646:
; inspect
task → #generator:state: 1331
</syntaxhighlight>
=={{header|Elixir}}==
{{trans|Erlang}}
<
def filter( source_pid, remove_pid ) do
first_remove = next( remove_pid )
Line 1,037 ⟶ 1,696:
end
IO.inspect Generator.task</
{{out}}
Line 1,043 ⟶ 1,702:
[529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089]
</pre>
=={{header|Emacs Lisp}}==
This code requires generator library which was introduced in Emacs 25.2
<syntaxhighlight lang="lisp">;; lexical-binding: t
(require 'generator)
(iter-defun exp-gen (pow)
(let ((i -1))
(while
(setq i (1+ i))
(iter-yield (expt i pow)))))
(iter-defun flt-gen ()
(let* ((g (exp-gen 2))
(f (exp-gen 3))
(i (iter-next g))
(j (iter-next f)))
(while
(setq i (iter-next g))
(while (> i j)
(setq j (iter-next f)))
(unless (= i j)
(iter-yield i)))))
(let ((g (flt-gen))
(o 'nil))
(dotimes (i 29)
(setq o (iter-next g))
(when (>= i 20)
(print o))))</syntaxhighlight>
=={{header|Erlang}}==
<syntaxhighlight lang="erlang">
-module( generator ).
Line 1,083 ⟶ 1,775:
receive {next, Pid} -> Pid ! erlang:round(math:pow(N, M) ) end,
power_loop( M, N + 1 ).
</syntaxhighlight>
{{out}}
<pre>
Line 1,092 ⟶ 1,784:
=={{header|F_Sharp|F#}}==
{{trans|C#}}
<
let squares = m 2
Line 1,102 ⟶ 1,794:
Seq.take 10 (Seq.skip 20 (``squares without cubes``))
|> Seq.toList |> printfn "%A"</
{{out}}
<pre>[529; 576; 625; 676; 784; 841; 900; 961; 1024; 1089]</pre>
=={{header|Factor}}==
Using lazy lists for our generators:
<syntaxhighlight lang="factor">USING: fry kernel lists lists.lazy math math.functions
prettyprint ;
IN: rosetta-code.generator-exponential
: mth-powers-generator ( m -- lazy-list )
[ 0 lfrom ] dip [ ^ ] curry lmap-lazy ;
: lmember? ( elt list -- ? )
over '[ unswons dup _ >= ] [ drop ] until nip = ;
: 2-not-3-generator ( -- lazy-list )
2 mth-powers-generator
[ 3 mth-powers-generator lmember? not ] <lazy-filter> ;
10 2-not-3-generator 20 [ cdr ] times ltake list>array .</syntaxhighlight>
{{out}}
<pre>
{ 529 576 625 676 784 841 900 961 1024 1089 }
</pre>
=={{header|Fantom}}==
Line 1,110 ⟶ 1,824:
Using closures to implement generators.
<
class Main
{
Line 1,151 ⟶ 1,865:
}
}
</syntaxhighlight>
{{out}}
Line 1,168 ⟶ 1,882:
=={{header|Forth}}==
<syntaxhighlight lang="forth">
\ genexp-rcode.fs Generator/Exponential for RosettaCode.org
Line 1,215 ⟶ 1,929:
:noname 0 Counter ! 1 Sqroot ! 1 Cbroot ! 0 (go) drop ;
execute cr bye
</syntaxhighlight>
{{out}}
<pre>
Line 1,222 ⟶ 1,936:
$
</pre>
=={{header|FreeBASIC}}==
{{trans|VBA}}
<syntaxhighlight lang="freebasic">Dim Shared As Long lastsquare, nextsquare, lastcube, midcube, nextcube
Function squares() As Long
lastsquare += nextsquare
nextsquare += 2
squares = lastsquare
End Function
Function cubes() As Long
lastcube += nextcube
nextcube += midcube
midcube += 6
cubes = lastcube
End Function
lastsquare = 1 : nextsquare = -1 : lastcube = -1 : midcube = 0 : nextcube = 1
Dim As Long cube, square
cube = cubes
For i As Byte = 1 To 30
Do
square = squares
Do While cube < square
cube = cubes
Loop
If square <> cube Then Exit Do
Loop
If i > 20 Then Print square;
Next i
Sleep</syntaxhighlight>
{{out}}
<pre>
Igual que la entrada de VBA.
</pre>
=={{header|FunL}}==
{{trans|Haskell}} (for the powers function)
{{trans|Scala}} (for the filter)
<
def
Line 1,233 ⟶ 1,986:
filtered( _:st, c ) = filtered( st, c )
println( filtered(powers(2), powers(3)).drop(20).take(10) )</
{{out}}
<pre>
Line 1,241 ⟶ 1,994:
=={{header|Go}}==
Most direct and most efficient on a single core is implementing generators with closures.
<
import (
Line 1,287 ⟶ 2,040:
}
fmt.Println()
}</
{{out}}
<pre>
Line 1,301 ⟶ 2,054:
A generator implemented as a goroutine, on the other hand, "returns" a value by sending it on a channel, and then the goroutine continues execution from that point.
This allows more flexibility in structuring code.
<
import (
Line 1,348 ⟶ 2,101:
}
fmt.Println()
}</
=={{header|Haskell}}==
Generators in most cases can be implemented using infinite lists in Haskell. Because Haskell is lazy, only as many elements as needed is computed from the infinite list:
<
powers :: Int -> [Int]
powers m = map (^ m) [0..]
squares :: [Int]
squares = powers 2
cubes :: [Int]
cubes = powers 3
foo :: [Int]
foo = filter (not . has cubes) squares
main :: IO ()
main = print $ take 10 $ drop 20
{{Out}}
<pre>[529,576,625,676,784,841,900,961,1024,1089]</pre>
Line 1,370 ⟶ 2,128:
Co-expressions let us circumvent the normal backtracking mechanism and get results where we need them.
<
write("Non-cube Squares (21st to 30th):")
Line 1,394 ⟶ 2,152:
}
}
end</
Note: The task could be written without co-expressions but would be likely be ugly.
Line 1,418 ⟶ 2,176:
Here is a generator for mth powers of a number:
<
N=: 0
create=: 3 :0
Line 1,427 ⟶ 2,185:
N=: N+1
n^M
)</
And, here are corresponding square and cube generators
<
stateyCube=: 3 conew 'mthPower'</
Here is a generator for squares which are not cubes:
<
N=: 0
next=: 3 :0"0
while. (-: <.) 3 %: *: n=. N do. N=: N+1 end. N=: N+1
*: n
)</
And here is an example of its use:
<
529 576 625 676 784 841 900 961 1024 1089</
That said, here is a more natural approach, for J.
<
squares=: 2 mthPower
cubes=: 3 mthPower
uncubicalSquares=: squares -. cubes</
The downside of this approach is that it is computing independent sequences. And for the "uncubicalSquares" verb, it is removing some elements from that sequence. So you must estimate how many values to generate. However, this can be made transparent to the user with a simplistic estimator:
<
Example use:
<
529 576 625 676 784 841 900 961 1024 1089</
=={{header|Java}}==
{{works with|java|8}}
<
import static java.util.stream.LongStream.generate;
Line 1,518 ⟶ 2,276:
return n * n * n++;
}
}</
<pre>529 576 625 676 784 841 900 961 1024 1089</pre>
=={{header|JavaScript}}==
===Procedural===
{{works with|Firefox 3.6 using JavaScript 1.7|}}
<syntaxhighlight lang="javascript">
function PowersGenerator(m) {
var n=0;
Line 1,563 ⟶ 2,322:
for( var x = 20; x < 30; x++ ) console.logfiltered.next());
</syntaxhighlight>
====ES6====
<
let e = 0;
while (1) { e++ && (yield Math.pow(e, n)); }
Line 1,585 ⟶ 2,344:
}
const filtered = filterGen(nPowerGen(2), nPowerGen(3), skip=20);</
<
for (let n = 0; n < 10; n++) {
console.log(filtered.next().value)
}</
<pre>529
576
Line 1,600 ⟶ 2,359:
1024
1089</pre>
===Functional===
====ES6====
Compositional derivation of custom generators:
{{Trans|Python}}
<syntaxhighlight lang="javascript">(() => {
'use strict';
// main :: IO()
const main = () => {
// powers :: Gen [Int]
const powers = n =>
fmapGen(
x => Math.pow(x, n),
enumFrom(0)
);
// xs :: [Int]
const xs = take(10, drop(20,
differenceGen(
powers(2),
powers(3)
)
));
console.log(xs);
// -> [529,576,625,676,784,841,900,961,1024,1089]
};
// GENERIC FUNCTIONS ----------------------------------
// Just :: a -> Maybe a
const Just = x => ({
type: 'Maybe',
Nothing: false,
Just: x
});
// Nothing :: Maybe a
const Nothing = () => ({
type: 'Maybe',
Nothing: true,
});
// Tuple (,) :: a -> b -> (a, b)
const Tuple = (a, b) => ({
type: 'Tuple',
'0': a,
'1': b,
length: 2
});
// differenceGen :: Gen [a] -> Gen [a] -> Gen [a]
function* differenceGen(ga, gb) {
// All values of generator stream a except any
// already seen in generator stream b.
const
stream = zipGen(ga, gb),
sb = new Set([]);
let xy = take(1, stream);
while (0 < xy.length) {
const [x, y] = Array.from(xy[0]);
sb.add(y);
if (!sb.has(x)) yield x;
xy = take(1, stream);
}
};
// drop :: Int -> [a] -> [a]
// drop :: Int -> Generator [a] -> Generator [a]
// drop :: Int -> String -> String
const drop = (n, xs) =>
Infinity > length(xs) ? (
xs.slice(n)
) : (take(n, xs), xs);
// enumFrom :: Enum a => a -> [a]
function* enumFrom(x) {
let v = x;
while (true) {
yield v;
v = 1 + v;
}
}
// fmapGen <$> :: (a -> b) -> Gen [a] -> Gen [b]
function* fmapGen(f, gen) {
let v = take(1, gen);
while (0 < v.length) {
yield(f(v[0]))
v = take(1, gen)
}
}
// fst :: (a, b) -> a
const fst = tpl => tpl[0];
// Returns Infinity over objects without finite length.
// This enables zip and zipWith to choose the shorter
// argument when one is non-finite, like cycle, repeat etc
// length :: [a] -> Int
const length = xs =>
(Array.isArray(xs) || 'string' === typeof xs) ? (
xs.length
) : Infinity;
// snd :: (a, b) -> b
const snd = tpl => tpl[1];
// take :: Int -> [a] -> [a]
// take :: Int -> String -> String
const take = (n, xs) =>
'GeneratorFunction' !== xs.constructor.constructor.name ? (
xs.slice(0, n)
) : [].concat.apply([], Array.from({
length: n
}, () => {
const x = xs.next();
return x.done ? [] : [x.value];
}));
// uncons :: [a] -> Maybe (a, [a])
const uncons = xs => {
const lng = length(xs);
return (0 < lng) ? (
lng < Infinity ? (
Just(Tuple(xs[0], xs.slice(1))) // Finite list
) : (() => {
const nxt = take(1, xs);
return 0 < nxt.length ? (
Just(Tuple(nxt[0], xs))
) : Nothing();
})() // Lazy generator
) : Nothing();
};
// zipGen :: Gen [a] -> Gen [b] -> Gen [(a, b)]
const zipGen = (ga, gb) => {
function* go(ma, mb) {
let
a = ma,
b = mb;
while (!a.Nothing && !b.Nothing) {
let
ta = a.Just,
tb = b.Just
yield(Tuple(fst(ta), fst(tb)));
a = uncons(snd(ta));
b = uncons(snd(tb));
}
}
return go(uncons(ga), uncons(gb));
};
// MAIN ---
return main();
})();</syntaxhighlight>
{{Out}}
<pre>[529,576,625,676,784,841,900,961,1024,1089]</pre>
=={{header|jq}}==
Line 1,610 ⟶ 2,531:
relevant state information. For convenience, a counter is usually
included. For generating i^m, therefore, we would have:
<
def pow(m): . as $in | reduce range(0;m) as $i (1; .*$in);
# state: [i, i^m]
def next_power(m): .[0] + 1 | [., pow(m) ];</
To make such generators easier to use, we shall define filters to
skip and to emit a specified number of items:
<
def skip(m; next):
if m <= 0 then . else next | skip(m-1; next) end;
Line 1,623 ⟶ 2,544:
# emit m states including the initial state
def emit(m; next):
if m <= 0 then empty else ., (next | emit(m-1; next)) end;</
'''Examples''':
<
[0,0] | emit(4; next_power(2)) | .[1]
# Generate all the values in the sequence i^3 less than 100:
[0,0] | recurse(next_power(3) | if .[1] < 100 then . else empty end) | .[1]</
'''An aside on streams'''
Line 1,638 ⟶ 2,559:
'''Part 2: selection from 2 ^ m'''
<
def last(f): reduce f as $i (null; $i);
Line 1,664 ⟶ 2,585:
| skip(20; filtered_next_power(2;3))
| emit(10; filtered_next_power(2;3))
| .[0][1]</
{{out}}
<
529
576
Line 1,676 ⟶ 2,597:
961
1024
1089</
=={{header|Julia}}==
The task can be achieved by using closures, iterators or tasks. Here is a solution using anonymous functions and closures.
<
take(gen::Function, n::Integer) = collect(gen() for _ in 1:n)
Line 1,700 ⟶ 2,621:
end
@show take(drop(genfilter(pgen(2), pgen(3)), 20), 10)</
{{out}}
Line 1,707 ⟶ 2,628:
=={{header|Kotlin}}==
Coroutines were introduced in version 1.1 of Kotlin but, as yet, are an experimental feature:
<
// compiled with flag -Xcoroutines=enable to suppress 'experimental' warning
Line 1,743 ⟶ 2,664:
ncs.drop(20).take(10).forEach { print("$it ") } // print 21st to 30th items
println()
}</
{{out}}
Line 1,751 ⟶ 2,672:
=={{header|Lingo}}==
Lingo neither supports coroutines nor first-class functions, and also misses syntactic sugar for implementing real generators. But in the context of
<syntaxhighlight lang="lingo">squares = script("generator.power").new(2)
cubes = script("generator.power").new(3)
filter = script("generator.filter").new(squares, cubes)
filter.skip(20)
res = []
i = 0
repeat
i = i + 1
if i>
end repeat</
{{out}}
Line 1,781 ⟶ 2,701:
Parent script "generator.power"
<
property _index
-- @constructor
on new (me, e)
me._exp = e
me._index = 0
return me
end
on exec (me, input)
me._index = me._index+1
input[1] = integer(power(me._index, me._exp))
return
end
on skip (me, steps)
me._index = me._index + steps
end
on reset (me)
me._index = 0
end</
Parent script "generator.
<
property _genf
-- @constructor
on new (me, genv, genf)
me._genv = genv
Line 1,824 ⟶ 2,737:
end
on exec (me, input)
repeat while TRUE
me._genv.exec(input)
Line 1,849 ⟶ 2,757:
end if
end repeat
return
end
on skip (me, steps)
repeat with i = 1 to steps
me.exec([])
end repeat
end
on reset (me)
me._genv.reset()
me._genf.reset()
end</syntaxhighlight>
=={{header|Lua}}==
Generators can be implemented both as closures and as coroutines. The following example demonstrates both.
<syntaxhighlight lang="lua">
--could be done with a coroutine, but a simple closure works just as well.
local function powgen(m)
Line 1,903 ⟶ 2,813:
end
end
</syntaxhighlight>
=={{header|M2000 Interpreter}}==
<syntaxhighlight lang="m2000 interpreter">
Module Generator {
PowGen = Lambda (e)
-> {
= Lambda
i=0, // closure
e // closure
-> {
i++
= i**e
}
}
Squares=Lambda
PowGen=PowGen(2) // closure
->{
= PowGen()
}
Cubes=Lambda
PowGen=PowGen(3) // closure
-> {
= PowGen()
}
Filter=Lambda
z=Squares(), // closure
Squares, // closure
m, // closure
Cubes // closure
->{
while m<z :m=cubes():end while
if z=m then z=Squares()
= z : z=Squares()
}
For i=1 to 20 : dropit=Filter() :Next i
Document doc$="Non-cubic squares (21st to 30th)"
Print doc$
doc$={
} \\ a new line to doc$
For i=1 to 10
f=Filter()
Print Format$("I: {0::-2}, F: {1}",i+20, f)
doc$=Format$("I: {0::-2}, F: {1}",i+20, f)+{
}
Next
Clipboard doc$
}
Generator
</syntaxhighlight>
{{out}}
<pre >
Non-cubic squares (21st to 30th)
I: 21, F: 529
I: 22, F: 576
I: 23, F: 625
I: 24, F: 676
I: 25, F: 784
I: 26, F: 841
I: 27, F: 900
I: 28, F: 961
I: 29, F: 1024
I: 30, F: 1089
</pre >
=={{header|Mathematica}} / {{header|Wolfram Language}}==
{{trans|VBA}}
Generators are not very natural in Mathemetica, because they avoid the use of lists and instead rely on sequential processing.
<syntaxhighlight lang="mathematica">lastsquare = 1;
nextsquare = -1;
lastcube = -1;
midcube = 0;
nextcube = 1;
Gensquares[] := Module[{},
lastsquare += nextsquare;
nextsquare += 2;
squares = lastsquare;
squares
]
Gencubes[] := Module[{},
lastcube += nextcube;
nextcube += midcube;
midcube += 6;
cubes = lastcube
]
c = Gencubes[];
Do[
While[True,
s = Gensquares[];
While[c < s,
c = Gencubes[];
];
If[s =!= c,
Break[]
];
];
If[i > 20,
Print[s]
]
,
{i, 30}
]</syntaxhighlight>
{{out}}
<pre>529
576
625
676
784
841
900
961
1024
1089</pre>
=={{header|Nim}}==
<syntaxhighlight lang
proc `^`*(base: Natural; exp: Natural): int =
var (base, exp) = (base, exp)
result = 1
while exp != 0:
if (exp and 1) != 0:
Line 1,916 ⟶ 2,942:
base *= base
proc next(s: Iterator): int =
for n in s(): return n
proc powers(m: Natural):
iterator it(): int {.closure.} =
for n in 0 ..
yield n ^ m
iterator filtered(s1, s2: Iterator): int =
var v = next(s1)
var f = next(s2)
Line 1,941 ⟶ 2,967:
i = 1
for x in filtered(squares, cubes):
if i > 20: echo x
if i
inc i</syntaxhighlight>
{{out}}
<pre>529
Line 1,957 ⟶ 2,982:
1024
1089</pre>
=={{header|OCaml}}==
Original version by [http://rosettacode.org/wiki/User:Vanyamil User:Vanyamil]
<syntaxhighlight lang="ocaml">
(* Task : Generator/Exponential
Version using the Seq module types, but transparently
*)
(*** Helper functions ***)
(* Generator type *)
type 'a gen = unit -> 'a node
and 'a node = Nil | Cons of 'a * 'a gen
(* Power function on integers *)
let power (base : int) (exp : int) : int =
let rec helper exp acc =
if exp = 0 then acc
else helper (exp - 1) (base * acc)
in
helper exp 1
(* Take (at most) n from generator *)
let rec take (n : int) (gen : 'a gen) : 'a list =
if n = 0 then []
else
match gen () with
| Nil -> []
| Cons (x, tl) -> x :: take (n - 1) tl
(* Stop existing generator at a given condition *)
let rec keep_while (p : 'a -> bool) (gen : 'a gen) : 'a gen = fun () ->
match gen () with
| Nil -> Nil
| Cons (x, tl) ->
if p x then Cons (x, keep_while p tl)
else Nil
(* Drop the first n elements of a generator *)
let rec drop (n : int) (gen : 'a gen) : 'a gen =
if n = 0 then gen
else
match gen () with
| Nil -> (fun () -> Nil)
| Cons (_, tl) -> drop (n - 1) tl
(* Filter based on predicate, lazily *)
let rec filter (p : 'a -> bool) (gen : 'a gen) : 'a gen = fun () ->
match gen () with
| Nil -> Nil
| Cons (x, tl) ->
if p x then Cons (x, filter p tl)
else filter p tl ()
(* Is this value inside this generator? Does not terminate for infinite streams! *)
let rec mem (val_ : 'a) (gen : 'a gen) : bool =
match gen () with
| Nil -> false
| Cons (x, tl) ->
if x = val_ then true
else mem val_ tl
(*** Task at hand ***)
(* Create a function that returns a generation of the m'th powers of the positive integers
starting from zero, in order, and without obvious or simple upper limit.
(Any upper limit to the generator should not be stated in the source but should be down
to factors such as the languages natural integer size limit or computational time/size).
*)
let power_gen k : int gen =
let rec generator n () =
Cons (power n k, generator (n + 1))
in
generator 0
(* Use it to create generators of squares and cubes *)
let squares = power_gen 2
let cubes = power_gen 3
(* Create a new generator that filters all cubes from the generator of squares. *)
let squares_no_cubes =
let filter_p square =
(* Get all cubes up to square *)
let cubes_up_to_n2 = keep_while ((>=) square) cubes in
not (mem square cubes_up_to_n2)
in
filter filter_p squares
(*** Output ***)
(* Drop the first 20 values from this last generator of filtered results, and then show the next 10 values. *)
let _ =
squares_no_cubes |> drop 20 |> take 10
</syntaxhighlight>
{{out}}
<pre>
- : int list = [529; 576; 625; 676; 784; 841; 900; 961; 1024; 1089]
</pre>
=={{header|PARI/GP}}==
Define two generator functions genpow() and genpow2().
<
genpow(p) = my(a=g[1]++);listput(g,[0,p]);()->g[a][1]++^g[a][2];
genpowf(p,f) = my(a=g[1]++);listput(g,[0,p]);(s=0)->my(q);while(ispower(p=g[a][1]++^g[a][2],f)||(s&&q++<=s),);p;</
''genpow(power)'' returns a function that returns a simple power generator.<br>
Line 1,998 ⟶ 3,122:
1024
1089</pre>
=={{header|PascalABC.NET}}==
<syntaxhighlight lang="delphi">
##
var ms: integer -> sequence of BigInteger := m -> 0.Step.Select(i -> BigInteger(i)**m);
var squares := ms(2);
var cubes := ms(3);
var filtered := squares.Where(square -> cubes.First(cube -> cube >= square) <> square);
filtered.Skip(20).Take(10).Println;
</syntaxhighlight>
{{out}}
<pre>
529 576 625 676 784 841 900 961 1024 1089
</pre>
=={{header|Perl}}==
These generators are anonymous subroutines, which are closures.
<
# generate and return the powers 0**m, 1**m, 2**m, ...
sub gen_pow {
Line 2,038 ⟶ 3,177:
my @answer;
push @answer, $squares_without_cubes->() for (1..10);
print "[", join(", ", @answer), "]\n";</
{{out}}<pre>[529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089]</pre>
=={{header|Phix}}==
<!--<syntaxhighlight lang="phix">(notonline)-->
<span style="color: #000080;font-style:italic;">--
-- demo\rosetta\Generator_Exponential.exw
-- ======================================
--</span>
<span style="color: #008080;">without</span> <span style="color: #008080;">js</span> <span style="color: #000080;font-style:italic;">-- tasks</span>
<span style="color: #004080;">bool</span> <span style="color: #000000;">terminate</span> <span style="color: #0000FF;">=</span> <span style="color: #004600;">false</span>
<span style="color: #004080;">atom</span> <span style="color: #000000;">res</span>
<span style="color: #008080;">procedure</span> <span style="color: #000000;">powers</span><span style="color: #0000FF;">(</span><span style="color: #004080;">integer</span> <span style="color: #000000;">p</span><span style="color: #0000FF;">)</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">0</span>
<span style="color: #008080;">while</span> <span style="color: #008080;">not</span> <span style="color: #000000;">terminate</span> <span style="color: #008080;">do</span>
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">power</span><span style="color: #0000FF;">(</span><span style="color: #000000;">i</span><span style="color: #0000FF;">,</span><span style="color: #000000;">p</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">task_suspend</span><span style="color: #0000FF;">(</span><span style="color: #000000;">task_self</span><span style="color: #0000FF;">())</span>
<span style="color: #000000;">task_yield</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">i</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
<span style="color: #008080;">constant</span> <span style="color: #000000;">squares</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">task_create</span><span style="color: #0000FF;">(</span><span style="color: #000000;">powers</span><span style="color: #0000FF;">,{</span><span style="color: #000000;">2</span><span style="color: #0000FF;">}),</span>
<span style="color: #000000;">cubes</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">task_create</span><span style="color: #0000FF;">(</span><span style="color: #000000;">powers</span><span style="color: #0000FF;">,{</span><span style="color: #000000;">3</span><span style="color: #0000FF;">})</span>
<span style="color: #004080;">atom</span> <span style="color: #000000;">square</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">cube</span>
<span style="color: #000000;">task_schedule</span><span style="color: #0000FF;">(</span><span style="color: #000000;">cubes</span><span style="color: #0000FF;">,</span><span style="color: #000000;">1</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">task_yield</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">cube</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">res</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #000000;">30</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">while</span> <span style="color: #000000;">1</span> <span style="color: #008080;">do</span>
<span style="color: #000000;">task_schedule</span><span style="color: #0000FF;">(</span><span style="color: #000000;">squares</span><span style="color: #0000FF;">,</span><span style="color: #000000;">1</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">task_yield</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">square</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">res</span>
<span style="color: #008080;">while</span> <span style="color: #000000;">cube</span><span style="color: #0000FF;"><</span><span style="color: #000000;">square</span> <span style="color: #008080;">do</span>
<span style="color: #000000;">task_schedule</span><span style="color: #0000FF;">(</span><span style="color: #000000;">cubes</span><span style="color: #0000FF;">,</span><span style="color: #000000;">1</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">task_yield</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">cube</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">res</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">square</span><span style="color: #0000FF;">!=</span><span style="color: #000000;">cube</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">></span><span style="color: #000000;">20</span> <span style="color: #008080;">then</span>
<span style="color: #0000FF;">?</span><span style="color: #000000;">square</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #000000;">terminate</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">1</span>
<span style="color: #0000FF;">{}</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">wait_key</span><span style="color: #0000FF;">()</span>
<!--</syntaxhighlight>-->
{{out}}
<pre>
Line 2,122 ⟶ 3,246:
{{trans|Python}}
{{works with|PHP|5.5+}}
<
function powers($m) {
for ($n = 0; ; $n++) {
Line 2,151 ⟶ 3,275:
$f->next();
}
?></
{{out}}
Line 2,169 ⟶ 3,293:
=={{header|PicoLisp}}==
Coroutines are available only in the 64-bit version.
<
(co (intern (pack 'powers M))
(for (I 0 (inc 'I))
Line 2,184 ⟶ 3,308:
(do 20 (filtered 2 3))
(do 10 (println (filtered 2 3)))</
{{out}}
<pre>529
Line 2,198 ⟶ 3,322:
=={{header|PL/I}}==
<syntaxhighlight lang="pl/i">
Generate: procedure options (main); /* 27 October 2013 */
declare j fixed binary;
Line 2,243 ⟶ 3,367:
end Generate;
</syntaxhighlight>
<pre>
20 dropped values:
Line 2,257 ⟶ 3,381:
{{works with|Python|2.6+ and 3.x}} (in versions prior to 2.6, replace <code>next(something)</code> with <code>something.next()</code>)
<
def powers(m):
Line 2,275 ⟶ 3,399:
squares, cubes = powers(2), powers(3)
f = filtered(squares, cubes)
print(list(islice(f, 20, 30)))</
{{out}}
<pre>[529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089]</pre>
Or, deriving custom generators compositionally:
{{Works with|Python|3.7}}
<syntaxhighlight lang="python">'''Exponentials as generators'''
from itertools import count, islice
# powers :: Gen [Int]
def powers(n):
'''A non-finite succession of integers,
starting at zero,
raised to the nth power.'''
def f(x):
return pow(x, n)
return map(f, count(0))
# main :: IO ()
def main():
'''Taking the difference between two derived generators.'''
print(
take(10)(
drop(20)(
differenceGen(powers(2))(
powers(3)
)
)
)
)
# GENERIC -------------------------------------------------
# differenceGen :: Gen [a] -> Gen [a] -> Gen [a]
def differenceGen(ga):
'''All values of ga except any
already seen in gb.'''
def go(a, b):
stream = zip(a, b)
bs = set([])
while True:
xy = next(stream, None)
if None is not xy:
x, y = xy
bs.add(y)
if x not in bs:
yield x
else:
return
return lambda gb: go(ga, gb)
# drop :: Int -> [a] -> [a]
# drop :: Int -> String -> String
def drop(n):
'''The sublist of xs beginning at
(zero-based) index n.'''
def go(xs):
if isinstance(xs, list):
return xs[n:]
else:
take(n)(xs)
return xs
return lambda xs: go(xs)
# take :: Int -> [a] -> [a]
# take :: Int -> String -> String
def take(n):
'''The prefix of xs of length n,
or xs itself if n > length xs.'''
return lambda xs: (
xs[0:n]
if isinstance(xs, list)
else list(islice(xs, n))
)
# MAIN ---
if __name__ == '__main__':
main()</syntaxhighlight>
{{Out}}
<pre>[529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089]</pre>
=={{header|Quackery}}==
<syntaxhighlight lang="quackery"> [ ' [ this -1 peek
this -2 peek **
1 this tally
done ]
swap join
0 join ] is expogen ( n --> [ )
[ ' [ this temp put
temp share -3 peek do
dup temp share share = iff
[ drop
temp share -2 peek do
temp take replace ] again
[ dup temp share share > iff
[ temp share -2 peek do
temp share replace ]
again ]
temp release
done ]
unrot
dip nested
dup dip nested
do 3 times join ] is taskgen ( [ [ --> [ )
2 expogen
3 expogen taskgen
20 times [ dup do drop ]
10 times [ dup do echo sp ]
drop</syntaxhighlight>
{{out}}
<pre>529 576 625 676 784 841 900 961 1024 1089 </pre>
=={{header|R}}==
<
{n = -1
function()
Line 2,306 ⟶ 3,556:
noncubic.squares()
for (i in 1:10)
message(noncubic.squares())</
=={{header|Racket}}==
<
#lang racket
Line 2,334 ⟶ 3,584:
[i 30] #:when (>= i 20))
x)
</syntaxhighlight>
{{out}}
Line 2,340 ⟶ 3,590:
'(529 576 625 676 784 841 900 961 1024 1089)
</pre>
=={{header|Raku}}==
(formerly Perl 6)
As with Haskell, generators are disguised as lazy lists in Raku.
<syntaxhighlight lang="raku" line>sub powers($m) { 0..* X** $m }
my @squares = powers(2);
my @cubes = powers(3);
sub infix:<with-out> (@orig, @veto) {
gather for @veto -> $veto {
take @orig.shift while @orig[0] before $veto;
@orig.shift if @orig[0] eqv $veto;
}
}
say (@squares with-out @cubes)[20 ..^ 20+10].join(', ');</syntaxhighlight>
{{out}}
<pre>529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089</pre>
=={{header|REXX}}==
<br>The generators (below, the <big> Gxxxxx </big> functions) lie dormant until a request is made for a specific generator index.
<
parse arg N .; if N=='' | N=="," then N=20 /*N not specified? Then use default.*/
@.= /* [↓] calculate squares,cubes,pureSq.*/
Line 2,378 ⟶ 3,649:
#=#+1; @.pureSquare.#=? /*assign next pureSquare. */
end /*j*/
return @.pureSquare.x</
'''output''' when using the default value:
<pre>
Line 2,398 ⟶ 3,669:
An iterator is a Ruby method that takes a block parameter, and loops the block for each element. So <tt>powers(2) { |i| puts "Got #{i}" }</tt> would loop forever and print Got 0, Got 1, Got 4, Got 9 and so on. Starting with Ruby 1.8.7, one can use <tt>Object#enum_for</tt> to convert an iterator method to an <tt>Enumerator</tt> object. The <tt>Enumerator#next</tt> method is a generator that runs the iterator method on a separate coroutine. Here <tt>cubes.next</tt> generates the next cube number.
<
def powers(m)
Line 2,417 ⟶ 3,688:
p squares_without_cubes.take(30).drop(20)
# p squares_without_cubes.lazy.drop(20).first(10) # Ruby 2.0+</
{{out}}
<pre>
Line 2,427 ⟶ 3,698:
Here is the correct solution, which obeys the ''requirement'' of ''three'' generators.
<
def powers(m)
Line 2,449 ⟶ 3,720:
answer = squares_without_cubes # third generator
20.times { answer.next }
p 10.times.map { answer.next }</
{{out}}
<pre>
Line 2,461 ⟶ 3,732:
Powers method is the same as the above.
{{trans|Python}}
<
return enum_for(__method__, s1, s2) unless block_given?
v, f = s1.next, s2.next
Line 2,474 ⟶ 3,745:
f = filtered(squares, cubes)
p f.take(30).last(10)
# p f.lazy.drop(20).first(10) # Ruby 2.0+</
Output is the same as the above.
=={{header|Rust}}==
<syntaxhighlight lang="rust">use std::cmp::Ordering;
use std::iter::Peekable;
fn powers(m: u32) -> impl Iterator<Item = u64> {
(0u64..).map(move |x| x.pow(m))
}
fn noncubic_squares() -> impl Iterator<Item = u64> {
NoncubicSquares {
squares: powers(2).peekable(),
cubes: powers(3).peekable(),
}
}
struct NoncubicSquares<T: Iterator<Item = u64>, U: Iterator<Item = u64>> {
squares: Peekable<T>,
cubes: Peekable<U>,
}
impl<T: Iterator<Item = u64>, U: Iterator<Item = u64>> Iterator for NoncubicSquares<T, U> {
type Item = u64;
fn next(&mut self) -> Option<u64> {
loop {
match self.squares.peek()?.cmp(self.cubes.peek()?) {
Ordering::Equal => self.squares.next(),
Ordering::Greater => self.cubes.next(),
Ordering::Less => return self.squares.next(),
};
}
}
}
fn main() {
noncubic_squares()
.skip(20)
.take(10)
.for_each(|x| print!("{} ", x));
println!();
}</syntaxhighlight>
{{out}}
<pre>529 576 625 676 784 841 900 961 1024 1089 </pre>
=={{header|Scala}}==
<
def main(args: Array[String]): Unit = {
def squares(n:Int=0):Stream[Int]=(n*n) #:: squares(n+1)
Line 2,491 ⟶ 3,805:
filtered(squares(), cubes()) drop 20 take 10 print
}
}</
Here is an alternative filter implementation using pattern matching.
<
case (sh#::_, ch#::ct) if (sh>ch) => filtered2(s, ct)
case (sh#::st, ch#::_) if (sh<ch) => sh #:: filtered2(st, c)
case (_#::st, _) => filtered2(st, c)
}</
{{out}}
<pre>529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089, empty</pre>
=={{header|Scheme}}==
===Scheme using conventional closures===
<syntaxhighlight lang="lisp">(define (power-seq n)
(let ((i 0))
(lambda ()
Line 2,528 ⟶ 3,843:
(newline))
(seq))
(loop seq (+ 1 i)))))</
{{out}}
<pre>576
Line 2,539 ⟶ 3,854:
1024
1089</pre>
===Scheme using ''call with current continuation''===
This method can be elaborated upon to, for instance, provide functionality similar to that of Icon co-expressions.
<syntaxhighlight lang="scheme">
;;; Generators using call/cc.
(cond-expand
(r7rs)
(chicken (import r7rs)))
(define-library (suspendable-procedures)
(export suspend)
(export make-generator-procedure)
(import (scheme base))
(begin
(define *suspend* (make-parameter (lambda (x) x)))
(define (suspend v) ((*suspend*) v))
(define (make-generator-procedure thunk)
;; This is for making a suspendable procedure that takes no
;; arguments when resumed. The result is a simple generator of
;; values.
(define (next-run return)
(define (my-suspend v)
(set! return (call/cc (lambda (resumption-point)
(set! next-run resumption-point)
(return v)))))
(parameterize ((*suspend* my-suspend))
(suspend (thunk))))
(lambda () (call/cc next-run)))
)) ;; end library (suspendable-procedures)
(import (scheme base))
(import (scheme case-lambda))
(import (scheme write))
(import (suspendable-procedures))
(define (make-integers-generator i0)
(make-generator-procedure
(lambda ()
(let loop ((i i0))
(suspend i)
(loop (+ i 1))))))
(define make-nth-powers-generator
(case-lambda
((n i0)
(define next-int (make-integers-generator i0))
(make-generator-procedure
(lambda ()
(let loop ()
(suspend (expt (next-int) n))
(loop)))))
((n)
(make-nth-powers-generator n 0))))
(define (make-filter-generator gen1 gen2)
(make-generator-procedure
(lambda ()
(let loop ((x1 (gen1))
(x2 (gen2)))
(cond ((= x1 x2) (loop (gen1) x2)) ; Skip this x1.
((< x1 x2) (begin ; Return this x1.
(suspend x1)
(loop (gen1) x2)))
(else (loop x1 (gen2))))))))
(define (gen-drop n)
(lambda (generator)
(make-generator-procedure
(lambda ()
(do ((i 0 (+ i 1)))
((= i n))
(generator))
(let loop ()
(suspend (generator))
(loop))))))
(define (gen-take n)
(lambda (generator)
(make-generator-procedure
(lambda ()
(do ((i 0 (+ i 1)))
((= i n))
(suspend (generator)))
(let loop ()
(suspend #f)
(loop))))))
(define my-generator
((gen-take 10)
((gen-drop 20)
(make-filter-generator
(make-nth-powers-generator 2)
(make-nth-powers-generator 3)))))
(let loop ()
(let ((x (my-generator)))
(when x
(display " ")
(display x)
(loop))))
(newline)
</syntaxhighlight>
{{out}}
Using Gauche Scheme.
<pre>$ gosh generator-exponential.scm
529 576 625 676 784 841 900 961 1024 1089</pre>
Using CHICKEN Scheme (which has efficient '''call/cc'''). You will need the '''r7rs''' egg.
<pre>$ csi -s generator-exponential.scm && ./a.out
529 576 625 676 784 841 900 961 1024 1089</pre>
=={{header|SenseTalk}}==
The ExponentialGenerator script is a generator object for exponential values.
<syntaxhighlight lang="sensetalk">// ExponentialGenerator.script
to initialize
set my base to 0
if my exponent is empty then set my exponent to 1 -- default if not given
end initialize
to handle nextValue
add 1 to my base
return my base to the power of my exponent
end nextValue</syntaxhighlight>
The FilteredGenerator takes source and filter generators. It gets values from the source generator but excludes those from the filter generator.
<syntaxhighlight lang="sensetalk">// FilteredGenerator.script
// Takes a source generator, and a filter generator, which must both produce increasing values
// Produces values from the source generator that don't match values from the filter generator
to initialize
set my nextFilteredValue to the nextValue of my filter
end initialize
to handle nextValue
put the nextValue of my source into value -- get a candidate value
-- advance the filter as needed if it is behind
repeat while my nextFilteredValue is less than or equal to value
-- advance value if it's equal to the next filtered value
if my nextFilteredValue = value then set value to my source's nextValue
set my nextFilteredValue to my filter's nextValue
end repeat
return value
end nextValue
</syntaxhighlight>
This script shows the use of both of the generators.
<syntaxhighlight lang="sensetalk">// Main.script to use the generators
set squares to new ExponentialGenerator with {exponent:2}
set cubes to new ExponentialGenerator with {exponent:3}
put "First 10 Squares:"
repeat 10 times
put squares.nextValue
end repeat
put "-" repeated 30 times
put "First 10 Cubes:"
repeat 10 times
put cubes.nextValue
end repeat
put "-" repeated 30 times
set filteredSquares to new FilteredGenerator with {
source: new ExponentialGenerator with {exponent:2},
filter: new ExponentialGenerator with {exponent:3}
}
repeat 20 times
get filteredSquares.nextValue
end repeat
put "Filtered Squares 21 to 30:"
repeat with n=21 to 30
put n & ":" && filteredSquares.nextValue
end repeat
</syntaxhighlight>
{{out}}
<pre>
First 10 Squares:
1
4
9
16
25
36
49
64
81
100
------------------------------
First 10 Cubes:
1
8
27
64
125
216
343
512
729
1000
------------------------------
Filtered Squares 21 to 30:
21: 529
22: 576
23: 625
24: 676
25: 784
26: 841
27: 900
28: 961
29: 1024
30: 1089
</pre>
=={{header|Sidef}}==
{{trans|Perl}}
<
var e = 0;
func { e++ ** m };
Line 2,569 ⟶ 4,111:
var answer = [];
10.times { answer.append(squares_without_cubes()) };
say answer;</
{{out}}
<pre>
[529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089]
</pre>
=={{header|SuperCollider}}==
<syntaxhighlight lang="supercollider">
f = { |m| {:x, x<-(0..) } ** m };
g = f.(2);
g.nextN(10); // answers [ 0, 1, 4, 9, 16, 25, 36, 49, 64, 81 ]
</syntaxhighlight>
patterns are stream generators:
<syntaxhighlight lang="supercollider">(
f = Pseries(0, 1)
g = f ** 2;
g.asStream.nextN(10); // answers [ 0, 1, 4, 9, 16, 25, 36, 49, 64, 81 ]
)
</syntaxhighlight>
supercollider has no "without" stream function, this builds one:
<syntaxhighlight lang="supercollider">(
var filter = { |a, b, func| // both streams are assumed to be ordered
Prout {
var astr, bstr;
var aval, bval;
astr = a.asStream;
bstr = b.asStream;
bval = bstr.next;
while {
aval = astr.next;
aval.notNil
} {
while {
bval.notNil and: { bval < aval }
} {
bval = bstr.next;
};
if(func.value(aval, bval)) { aval.yield };
}
}
};
var without = filter.(_, _, { |a, b| a != b }); // partially apply function
f = Pseries(0, 1);
g = without.(f ** 2, f ** 3);
h = g.drop(20);
h.asStream.nextN(10);
)
answers: [ 529, 576, 625, 676, 784, 841, 900, 961, 1024, 1089 ]
</syntaxhighlight>
=={{header|Swift}}==
<
let power = Double(m)
var cur: Double = 0
Line 2,622 ⟶ 4,216:
//961
//1024
//1089</
=={{header|Tcl}}==
Line 2,680 ⟶ 4,222:
Tcl implements generators in terms of coroutines.
If these generators were terminating, they would finish by doing <code>return -code break</code> so as to terminate the calling loop context that is doing the extraction of the values from the generator.
<
proc powers m {
Line 2,710 ⟶ 4,252:
for {} {$i<30} {incr i} {
puts [filtered]
}</
{{out}}
<pre>
Line 2,723 ⟶ 4,265:
1024
1089
</pre>
=={{header|Ursalang}}==
<syntaxhighlight lang="ursalang">let count = gen() {
var n = 0
loop {
yield n
n := n + 1
}
}
let powers = gen(m) {
for n of count() {
yield n ** m
}
}
let filtered = gen(s1, s2) {
var v = s1()
var f = s2()
loop {
if v > f {
f := s2()
continue
} else if v < f {
yield v
}
v := s1()
}
}
let squares = powers(2)
let cubes = powers(3)
let f = filtered(squares, cubes)
// Drop first 20 items.
for i of range(20) {f()}
// Print next 10 items.
for i of range(10) {print(f())}</syntaxhighlight>
=={{header|VBA}}==
<syntaxhighlight lang="vb">Public lastsquare As Long
Public nextsquare As Long
Public lastcube As Long
Public midcube As Long
Public nextcube As Long
Private Sub init()
lastsquare = 1
nextsquare = -1
lastcube = -1
midcube = 0
nextcube = 1
End Sub
Private Function squares() As Long
lastsquare = lastsquare + nextsquare
nextsquare = nextsquare + 2
squares = lastsquare
End Function
Private Function cubes() As Long
lastcube = lastcube + nextcube
nextcube = nextcube + midcube
midcube = midcube + 6
cubes = lastcube
End Function
Public Sub main()
init
cube = cubes
For i = 1 To 30
Do While True
square = squares
Do While cube < square
cube = cubes
Loop
If square <> cube Then
Exit Do
End If
Loop
If i > 20 Then
Debug.Print square;
End If
Next i
End Sub</syntaxhighlight>{{out}}
<pre> 529 576 625 676 784 841 900 961 1024 1089 </pre>
=={{header|Visual Basic .NET}}==
'''Compiler:''' >= Visual Studio 2012
<syntaxhighlight lang="vbnet">Module Program
Iterator Function IntegerPowers(exp As Integer) As IEnumerable(Of Integer)
Dim i As Integer = 0
Do
Yield CInt(Math.Pow(i, exp))
i += 1
Loop
End Function
Function Squares() As IEnumerable(Of Integer)
Return IntegerPowers(2)
End Function
Function Cubes() As IEnumerable(Of Integer)
Return IntegerPowers(3)
End Function
Iterator Function SquaresWithoutCubes() As IEnumerable(Of Integer)
Dim cubeSequence = Cubes().GetEnumerator()
Dim nextGreaterOrEqualCube As Integer = 0
For Each curSquare In Squares()
Do While nextGreaterOrEqualCube < curSquare
cubeSequence.MoveNext()
nextGreaterOrEqualCube = cubeSequence.Current
Loop
If nextGreaterOrEqualCube <> curSquare Then Yield curSquare
Next
End Function
Sub Main()
For Each x In From i In SquaresWithoutCubes() Skip 20 Take 10
Console.WriteLine(x)
Next
End Sub
End Module</syntaxhighlight>
More concise but slower implementation that relies on LINQ-to-objects to achieve generator behavior (runs slower due to re-enumerating Cubes() for every element of Squares()).
<syntaxhighlight lang="vbnet"> Function SquaresWithoutCubesLinq() As IEnumerable(Of Integer)
Return Squares().Where(Function(s) s <> Cubes().First(Function(c) c >= s))
End Function</syntaxhighlight>
{{out}}
<pre>529
576
625
676
784
841
900
961
1024
1089</pre>
=={{header|Wren}}==
Closure based solution. Similar approach to Go (first example).
<syntaxhighlight lang="wren">var powers = Fn.new { |m|
var i = 0
return Fn.new {
var p = i.pow(m)
i = i + 1
return p
}
}
var squaresNotCubes = Fn.new { |squares, cubes|
var sq = squares.call()
var cu = cubes.call()
return Fn.new {
var p
while (true) {
if (sq < cu) {
p = sq
sq = squares.call()
return p
}
if (sq == cu) sq = squares.call()
cu = cubes.call()
}
}
}
var squares = powers.call(2)
var cubes = powers.call(3)
var sqNotCu = squaresNotCubes.call(squares, cubes)
for (i in 0..29) {
var p = sqNotCu.call()
if (i > 19) System.write("%(p) ")
}
System.print()</syntaxhighlight>
{{out}}
<pre>
529 576 625 676 784 841 900 961 1024 1089
</pre>
=={{header|XPL0}}==
<
func Gen(M); \Generate Mth powers of positive integers
Line 2,750 ⟶ 4,476:
[for I:= 1 to 20 do Filter; \drop first 20 values
for I:= 1 to 10 do [IntOut(0, Filter); ChOut(0, ^ )]; \show next 10 values
]</
{{out}}
Line 2,760 ⟶ 4,486:
{{trans|Python}}
Generators are implemented with fibers (aka VMs) and return [lazy] iterators.
<
var squared=Utils.Generator(powers,2), cubed=Utils.Generator(powers,3);
Line 2,772 ⟶ 4,498:
var f=Utils.Generator(filtered,squared,cubed);
f.drop(20);
f.walk(10).println();</
{{out}}
<pre>L(529,576,625,676,784,841,900,961,1024,1089)</pre>
Line 2,780 ⟶ 4,506:
it just has been rewritten in a more functional style.
{{trans|Clojure}}
<
var squared=powers(2), cubed=powers(3);
Line 2,789 ⟶ 4,515:
}
var f=[0..].tweak(filtered.fp(squared,cubed))
f.drop(20).walk(10).println();</
|