Introspection

From Rosetta Code
Jump to: navigation, search
Task
Introspection
You are encouraged to solve this task according to the task description, using any language you may know.

This task asks to

  • verify the version/revision of your currently running (compiler/interpreter/byte-compiler/runtime environment/whatever your language uses) and exit if it is too old.
  • check whether the variable "bloop" exists and whether the math-function "abs()" is available and if yes compute abs(bloop).

Extra credit:

  • Report the number of integer variables in global scope, and their sum.


Contents

[edit] Ada

Ada doesn't allow you to ask about compiler versions, but you can query specific parameters of the target, such as the range of the standard integer type, or the precision of the standard floating point type:

with Ada.Integer_Text_IO, Ada.Text_IO;
procedure Introspection is
use Ada.Integer_Text_IO, Ada.Text_IO;
begin
Put ("Integer range: ");
Put (Integer'First);
Put (" .. ");
Put (Integer'Last);
New_Line;
 
Put ("Float digits: ");
Put (Float'Digits);
New_Line;
end Introspection;

[edit] Aikido

The version of the Aikido interpreter is in the global scope variable version. AIkido doesn't have abs but it does have fabs. Getting the variables in main involves getting their names and then evaluating them as an expression in order to retrieve their type.

 
import math
 
if (version < 144) {
throw "Version of aikido is too old"
}
 
var bloop = -1.4
 
// Math package doesn't have 'abs'. We'll use 'fabs' instead.
if ("fabs" in Math) {
if ("bloop" in main) {
println ("fabs(bloop) is " + eval ("Math.fabs(bloop)"))
}
}
 
var x = 104
var y = 598
var z = "hello"
var a = 1234
 
function count_ints {
// there are builtin integer variables that we don't want to count. There are
// 3 of them
var intcount = 0
// map of builtin variables we want to ignore
var ignore = {"version":true, "int":true, "integer":true}
var sum = 0
 
// the 'split' function can be used to split a block into a vector of the names
// of the variables within it
foreach v split (main, 0) {
var varname = v
try {
var value = eval (varname)
if (typeof(value) == "integer") {
if (varname in ignore) {
continue
}
intcount++
sum += value
}
} catch (e) {
// ignore exception
}
}
println ("There are " + intcount + " integer variables in the global scope")
println ("Their sum is " + sum)
}
 
count_ints()
 
 
 

Here is the result:

fabs(bloop) is 1.4
There are 3 integer variables in the global scope
Their sum is 1936


[edit] ALGOL 68

ALGOL 68 doesn't allow you to ask about compiler versions, but you can use constants specifying parameters of the target, such as the range of the standard integer type, or the precision of the standard floating point type.

Also: The constant(s) int lengths (real lengths) is the number (+1) of long precision types of int (reals) available at run time.

Translation of: Ada
Works with: ALGOL 68 version Standard - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8.8d.fc9.i386
BEGIN
print (("Integer range: ", -max int, " .. ", max int, new line));
print (("Integer digits: ", int width, new line));
print (("Float range: ", -max real, " .. ", max real, new line));
print (("Float digits: ", real width, new line))
END

Output:

Integer range: -2147483647 .. +2147483647
Integer digits:         +10
Float range: -1.79769313486235e+308 .. +1.79769313486235e+308
Float digits:         +15

The types of a value can also - crudely - be determined at run time. This is most useful for ALGOL 68's tagged unions, but it can also be used on any value. Note also that if a type is unioned with a void, then the empty value can be set to indicate that a variable has not been formally initialised to a value.

The following code demonstrates tagged-union introspection:

Works with: ALGOL 68 version Revision 1 - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
BEGIN
MODE SSMODES = UNION(SHORT SHORT BITS, SHORT SHORT BYTES, #SHORT SHORT CHAR,#
SHORT SHORT INT, SHORT SHORT REAL, SHORT SHORT COMPL);
MODE SMODES = UNION(SHORT BITS, SHORT BYTES, #SHORT CHAR,#
SHORT INT, SHORT REAL, SHORT COMPL);
MODE NMODES = UNION(BITS, BYTES, CHAR, INT, REAL, COMPL);
MODE LMODES = UNION(LONG BITS, LONG BYTES, #LONG CHAR,#
LONG INT, LONG REAL, LONG COMPL);
MODE LLMODES = UNION(LONG LONG BITS, LONG LONG BYTES, #LONG LONG CHAR,#
LONG LONG INT, LONG LONG REAL, LONG LONG COMPL);
MODE XMODES = UNION(BOOL, SEMA, STRING, VOID, CHANNEL, FILE, FORMAT);
 
MODE MODES = UNION(SSMODES, SMODES, NMODES, LLMODES, LMODES, XMODES);
 
OP REPRTYPEOF = (MODES val)STRING:
CASE val IN
(VOID):"VOID",
(INT):"INT",(SHORT INT):"SHORT INT",(SHORT SHORT INT):"SHORT SHORT INT",
(LONG INT):"LONG INT",(LONG LONG INT):"LONG LONG INT",
(REAL):"REAL",(SHORT REAL):"SHORT REAL",(SHORT SHORT REAL):"SHORT SHORT REAL",
(LONG REAL):"LONG REAL",(LONG LONG REAL):"LONG LONG REAL",
(COMPL):"COMPL",(SHORT COMPL):"SHORT COMPL",(SHORT SHORT COMPL):"SHORT SHORT COMPL",
(LONG COMPL):"LONG COMPL",(LONG LONG COMPL):"LONG LONG COMPL",
(BITS):"BITS",(SHORT BITS):"SHORT BITS",(SHORT SHORT BITS):"SHORT SHORT BITS",
(LONG BITS):"LONG BITS",(LONG LONG BITS):"LONG LONG BITS",
(BYTES):"BYTES",(SHORT BYTES):"SHORT BYTES",(SHORT SHORT BYTES):"SHORT SHORT BYTES",
(LONG BYTES):"LONG BYTES",(LONG LONG BYTES):"LONG LONG BYTES",
(CHAR):"CHAR",#(SHORT CHAR):"SHORT CHAR",(SHORT SHORT CHAR):"SHORT SHORT CHAR",
(LONG CHAR):"LONG CHAR",(LONG LONG CHAR):"LONG LONG CHAR",#

(BOOL):"BOOL",
(STRING):"STRING",
(SEMA):"SEMA",
(CHANNEL):"CHANNEL",
(FILE):"FILE",
(FORMAT):"FORMAT"
OUT
"ARRAY, PROC or STRUCT"
ESAC;
 
[]MODES x = (EMPTY, 1, 2.0, 3I4, SHORT SHORT 5, SHORT 6, LONG 7, LONG LONG 8,
8r666, bytes pack("abc"), TRUE, "xyz", LEVEL 1,
stand in channel, stand in, $ddd$);
 
STRING sep := "";
print(("Array member types: "));
FOR i TO UPB x DO
print((sep,REPRTYPEOF x[i]));
sep := ", "
OD
END

Output:

Array member types: VOID, INT, REAL, COMPL, INT, INT, LONG INT, LONG LONG INT, BITS, BYTES, BOOL, STRING, SEMA, CHANNEL, FILE, FORMAT


User defined "typeof" operator:

Algol68 permits the use of "operator overloading" over different types of variables. Hence the user is able to define their own introspecting "typeof" operator.

Works with: ALGOL 68 version Revision 1 - no extensions to language used
Works with: ALGOL 68G version Any - tested with release algol68g-2.3.3.
File: Typeof_operator.a68
#!/usr/local/bin/a68g --script #
 
OP TYPEOF = (INT skip)STRING: "INT";
OP TYPEOF = (CHAR skip)STRING: "CHAR";
OP TYPEOF = (REAL skip)STRING: "REAL";
OP TYPEOF = (COMPL skip)STRING: "COMPL";
 
printf(($g" "$,TYPEOF 1, TYPEOF "x", TYPEOF pi, TYPEOF (0 I 1 ), $l$))
Output:
INT CHAR REAL COMPL 


Array bounds can also be inspected:

Works with: ALGOL 68 version Revision 1- no extensions to language used.
Works with: ALGOL 68G version Any - tested with release algol68g-2.3.3.
Works with: ELLA ALGOL 68 version Any (with appropriate job cards)
File: Introspection_array_bounds.a68
#!/usr/local/bin/a68g --script #
 
[]INT x = (5,4,3,2,1);
 
print(("x =", x, new line));
print(("LWB x =", LWB x, ", UPB x = ",UPB x, new line))
Output:
x =         +5         +4         +3         +2         +1
LWB x =         +1, UPB x =          +5

[edit] AutoHotkey

if (A_AhkVersion < "1.0.48.03")
{
MsgBox % "you are using" . A_AhkVersion . "`nplease upgrade to" . "1.0.48.03"
ExitApp
}
bloop = -3
if bloop
if IsFunc("abs")
MsgBox % abs(bloop)
return

[edit] AWK

 
# syntax: GAWK -f INTROSPECTION.AWK
BEGIN {
if (PROCINFO["version"] < "4.1.0") {
print("version is too old")
exit(1)
}
bloop = -1
if (PROCINFO["identifiers"]["abs"] == "user" && bloop != "") {
printf("bloop = %s\n",bloop)
printf("abs(bloop) = %s\n",abs(bloop))
}
exit(0)
}
function abs(x) { if (x >= 0) { return x } else { return -x } }
 

output:

bloop = -1
abs(bloop) = 1

[edit] BBC BASIC

      IF VAL(FNversion) < 5.94 THEN PRINT "Version is too old" : END
 
ON ERROR LOCAL PRINT "Variable 'bloop' doesn't exist" : END
test = bloop
RESTORE ERROR
 
ON ERROR LOCAL PRINT "Function 'FNabs()' is not defined" : END
test = ^FNabs()
RESTORE ERROR
 
PRINT FNabs(bloop)
END
 
DEF FNversion
LOCAL F%, V$
F% = OPENOUT(@tmp$+"version.txt")
OSCLI "OUTPUT "+STR$F%
*HELP
*OUTPUT 0
PTR #F% = 0
INPUT #F%,V$
CLOSE #F%
= RIGHT$(V$,5)

[edit] C

Determining the make and version of the compiler, C standard, and environment features is one of the primary uses of the C preprocessor. This has allowed C to become the lingua franca of the open source movement.

Works with: C version 94 and later
#if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901L
#pragma error("C compiler must adhere to at least C99 for the following code.")
#else
/* rest of file */
#endif

However, there is no facility in C for checking whether individual variables and functions have been declared. In open source, the GNU autotools are often used for this purpose, doing this kind of check in a shell script and defining symbols such as HAVE_ABS which can be checked by the preprocessor.

[edit] Clojure

Partial answer...

 
; check Java version
(let [version (Double/parseDouble (re-find #"\d*\.\d*" (System/getProperty "java.version")))]
(if (>= version 1.5)
(println "Version ok")
(throw (Error. "Bad version"))))
 
; check Clojure version
(let [version (Double/parseDouble (re-find #"\d*\.\d*" (clojure-version)))]
(if (>= version 1.0)
(println "Version ok")
(throw (Error. "Bad version"))))
 


[edit] Common Lisp

(let* ((ver (lisp-implementation-version))
(major (parse-integer ver :start 0 :end (position #\. ver))))
#+lispworks (assert (>= 5 major) () "Requires Lispworks version 5 or above")
#+clisp (assert (>= 2 major) () "Requires CLISP 2.n")
)
(defvar bloop -4)
(if (and (fboundp 'abs)
(boundp 'bloop))
(format t "~d~%" (abs bloop)))

The list-all-packages and do-symbols forms enable a lisp program to examine all symbols and these can be tested to identify integer variables.

(let ((sum 0)
(ints '()))
(loop for pkg in (list-all-packages)
do (do-symbols (s pkg)
(when (and (boundp s)
(integerp (symbol-value s)))
(push s ints)
(incf sum (symbol-value s)))))
(format t "there are ~d integer variables adding up to ~d~%"
(length ints) sum))

[edit] D

With extra credit.

// Some module-level variables (D doesn't have a global scope).
immutable x = 3, y = 100, z = 3_000;
short w = 1; // Not an int, must be ignored.
immutable s = "some string"; // Not an int, must be ignored.
 
void main() {
import std.compiler, std.math, std.traits;
 
// Compile-time constants of the compiler version:
static assert(version_major > 1 && version_minor > 50,
"I can't cope with this compiler version.");
 
immutable bloop = 10;
 
// To check if something compiles:
static if (__traits(compiles, bloop.abs)) {
pragma(msg, "The expression is compilable.");
auto x = bloop.abs;
} else {
pragma(msg, "The expression can't be compiled.");
}
 
import std.stdio;
immutable s = 10_000; // Not at module scope, must be ignored.
 
int tot = 0;
/*static*/ foreach (name; __traits(allMembers, mixin(__MODULE__)))
static if (is(int == Unqual!(typeof(mixin("." ~ name)))))
tot += mixin("." ~ name);
writeln("Total of the module-level ints (could overflow): ", tot);
}
Output:
The expression is compilable.
Total of the module-level ints (could overflow): 3103

[edit] Erlang

Erlang does not have global variables so I look for a function bloop/0 that returns an integer. Moreover, I sum the available modules, instead of the unavailable global integers.

 
-module( introspection ).
 
-export( [task/0] ).
 
task() ->
exit_if_too_old( erlang:system_info(otp_release) ),
Bloop = lists:keyfind( bloop, 1, ?MODULE:module_info(functions) ),
Abs = lists:keyfind( abs, 1, erlang:module_info(exports) ),
io:fwrite( "abs( bloop ) => ~p~n", [call_abs_with_bloop(Abs, Bloop)] ),
io:fwrite( "Number of modules: ~p~n", [erlang:length(code:all_loaded())] ).
 
 
 
bloop() -> -1.
 
call_abs_with_bloop( {abs, 1}, {bloop, 0} ) -> erlang:abs( bloop() );
call_abs_with_bloop( _Missing, _Not_here ) -> abs_and_bloop_missing.
 
exit_if_too_old( Release ) when Release < "R13A" -> erlang:exit( too_old_release );
exit_if_too_old( _Release ) -> ok.
 
Output:
18> introspection:task().
abs( bloop ) => 1
Number of modules: 110

[edit] Factor

Check for build number and execute a quotation if it's too old. (There are no such things as versions for Factor yet.)

: if-older ( n true false -- )
[ build > ] 2dip if ; inline
 
: when-older ( n true -- )
[ ] if-older ; inline
: unless-older ( n false -- )
[ [ ] ] dip if-older ; inline
 
900 [ "Your version of Factor is too old." print 1 exit ] when-older

It is possible to test if a function or a variable exists (search), but that shouldn't be used outside of parsing.

"bloop" search [
get [
"abs" search [ execute( n -- n' ) ] when*
] [ 0 ] if*
] [ 0 ] if*

On the other hand, it is possible to search the global namespace for integer variables:

USING: assocs formatting kernel math namespaces ;
 
0 0
global [
nip dup integer? [ + [ 1 + ] dip ] [ drop ] if
] assoc-each
"There are %d integer variables, the sum is %d\n" printf

[edit] GAP

# Apply a function to a value, given variable names for both function and value
CheckEval := function(fun, val)
local f, x;
if IsBoundGlobal(fun) and IsBoundGlobal(val) then
f := ValueGlobal(fun);
x := ValueGlobal(val);
return f(x);
fi;
end;
 
bloop := -1;
CheckEval("AbsInt", "bloop");
# 1
 
 
# Sum of integer variables
GlobalIntegers := function()
local s, x;
s := 0;
for name in SortedList(NamesGVars()) do
if IsBoundGlobal(name) then
x := ValueGlobal(name);
if IsInt(x) then
Print(name, " ", x, "\n");
s := s + x;
fi;
fi;
od;
return s;
end;

[edit] Go

Task variance: "exit if it is too old" is not done here. Go version strings do not present an easily interpreted chronology. This version of the program simply prints the version string.

package main
 
import (
"debug/elf"
"debug/gosym"
"fmt"
"log"
"math"
"os"
"runtime"
)
 
var bloop = -3.4
 
func main() {
fmt.Println("task 1: verify version")
fmt.Println(" program compiled with", runtime.Version())
 
fmt.Println("task 2: check for presence of variable and function")
// inspect ELF symbol table
f, err := elf.Open(os.Args[0])
if err != nil {
log.Fatal(err)
}
defer f.Close()
symSection := f.Section(".gosymtab")
lineSection := f.Section(".gopclntab")
textSection := f.Section(".text")
if symSection == nil || lineSection == nil || textSection == nil {
log.Fatal("symbolic information not found")
}
symData, err := symSection.Data()
if err != nil {
log.Fatal(err)
}
lineData, err := lineSection.Data()
if err != nil {
log.Fatal(err)
}
table, err := gosym.NewTable(symData,
gosym.NewLineTable(lineData, textSection.Addr))
if err != nil {
log.Fatal(" ", err)
}
var foundBloop, foundFabs bool
for _, s := range table.Syms {
if s.Name == "main.bloop" {
foundBloop = true
fmt.Println(" bloop symbol table entry:", s)
} else if s.Name == "math.Abs" {
foundFabs = true
fmt.Println(" abs symbol table entry:", s)
}
}
if foundBloop && foundFabs {
fmt.Println(" bloop: ", bloop)
fmt.Println(" abs(bloop): ", math.Abs(bloop))
}
}
Output:
task 1: verify version
   program compiled with go1.0.2
task 2: check for presence of variable and function
   bloop symbol table entry: {5468424 68 main.bloop 273827584 <nil>}
   abs symbol table entry: {4404832 84 math.Abs 943802368 0xf8401fc190}
   bloop:      -3.4
   abs(bloop):  3.4

Work to do for extra credit involves not just locating symbols, but decoding the fields of the the symbol table entries. Note that once this is done, the basic task could be improved to compute abs(bloop) by accessing values located from symbol table data only, and the expression math.Abs(bloop) would not have to appear in the source code. This would seem in the spirit of the task.

[edit] E

Version:

def version := interp.getProps()["e.version"]

(There is no built-in version comparison, and the author of this example assumes that implementing a version comparison algorithm isn't the point of this task.)

Existence:

escape fail {
def &x := meta.getState().fetch("&bloop", fn { fail("no bloop") })
if (!x.__respondsTo("abs", 0)) { fail("no abs") }
x.abs()
}

This will return either bloop.abs(), "no bloop", or "no abs".

Sum of integers:

{
var sum := 0
for &x in interp.getTopScope() { sum += try { x :int } catch _ { 0 } }
sum
}

try rather than an ordinary type check is used because in general a slot might be broken; this way we skip over all read failures as well as non-integers. The block around the code ensures that the sum variable itself will not be involved in the computation.

[edit] Forth

Standard Forth doesn't necessarily provide for version numbers, but you can query information about the environment at interpretation time:

s" MAX-U" environment? [IF]
0xffffffff <> [IF] .( Requires 32 bits! ) bye [THEN]
[THEN]
 
[defined] bloop [if]
[defined] abs [if]
bloop @ abs
[then] [then]

4tH is able to fulfill all requirements. Note that since only one variable has been declared, the sum of all integer (user)variables is consequently the value of that variable.

Works with: 4tH version 3.62.2
[hex] 362 [decimal] 4TH# - [if] [abort] [then]
 
-32 value bloop
[defined] bloop [if]
[defined] abs [if]
bloop abs . cr
[then]
[then]
 
0 last cell+ first over over - .( User variables: ) .
?do i @ + loop .( Sum: ) . cr

Output:

32
User variables: 1 Sum: -32

[edit] Haskell

import Data.Version
import Control.Monad
import System.Info
 
minGHCVersion = Version [6, 8] []
 
main = when (compilerName == "ghc" && compilerVersion < minGHCVersion) $
fail "Compiler too old."

No means exists of checking whether a variable exists at runtime. The set of variables that exist in any given scope is fixed at compile-time.

[edit] Icon and Unicon

global bloop
 
procedure main(A)
if older(11,7) then stop("Must have version >= 11.7!")
bloop := -5 # global variable
floop := -11.3 # local variable
write(proc("abs")(variable("bloop"))
write(proc("abs")(variable("floop"))
end
 
procedure older(maj,min)
&version ? {
(tab(find("Version ")),move(*"Version "))
major := 1(tab(upto('.')),move(1))
minor := tab(upto('.'))
return (major < maj) | ((major = maj) & (minor < min))
}
end

Sample run:

->introspect
5
11.3
->

[edit] Inform 7

Inform 7 doesn't have built-in functionality for checking the runtime version number, but the version number is available and can be read by including a snippet of Inform 6 code. The address and format of the version number vary according to the virtual machine being targeted.

Home is a room.
 
When play begins:
let V be the current runtime version;
if V is less than the required runtime version:
say "Version [required runtime version] required, but [V] found.";
otherwise:
say "Your interpreter claims version [V].";
end the story.
 
A version is a kind of value.
 
Section - Checking the version (for Glulx only)
 
1.255.255 specifies a version with parts major, minor (without leading zeros), and subminor (without leading zeros).
 
To decide which version is current runtime version: (- (0-->1) -).
To decide which version is required runtime version: decide on 3.1.2.
 
Section - Checking the version (for Z-machine only)
 
1.255 specifies a version with parts major and minor (without leading zeros).
 
To decide which version is current runtime version: (- ($32-->0) -).
To decide which version is required runtime version: decide on 1.1.

It's not possible to check for the existence of functions (invoking a nonexistent phrase causes a compile-time error) or list global variables.

[edit] Io

if(System version < 20080000, exit)
 
if(hasSlot("bloop") and bloop hasSlot("abs"), bloop abs)

Io can also inspect the source code of methods written in Io:

getSlot("arbitraryMethod") code

[edit] J

Exit if we're running an old version of J (earlier than version 6, which is current as of this writing), giving version number as the exit status:

6 (2!:55@:]^:>) 0 ". 1 { 9!:14''

Compute abs(bloop) if abs is a function and bloop is data:

".(#~3 0*./ .=4!:0@;:)'abs bloop'

Extra credit: report the number of integer variables in global scope, and their sum:

((],&(+/);@#~)((=<.)@[^:](''-:$)*.0=0{.@#,)&>)".&.>4!:1]0

This last expression is longer than the others, because it has a couple of extra guard checks; in J, the programmer doesn't need to care if the data is a single number or an array, or what hardware representation is used for numbers (32-bit int, IEEE float, etc).

So this expression takes pains to emulate solutions in other languages (i.e. only reports globals that are single numbers, and whose value = floor(value), so that even if the number is represented as a float in the machine, you still get the right answer).

[edit] Java

You can't see if a variable or function is available in Java (it will be a compile time error if you try to use them when you they aren't available), but you can check the version number using the System class:

public class VersCheck {
public static void main(String[] args) {
String vers = System.getProperty("java.version");
vers = vers.substring(0,vers.indexOf('.')) + "." + //some String fiddling to get the version number into a usable form
vers.substring(vers.indexOf('.')+1,vers.lastIndexOf('.'));
if(Double.parseDouble(vers) >= 1.5){
System.out.println("YAY!");
}else{
System.err.println("Must use Java >=1.5");
}
}
}

[edit] JavaScript

It is generally out of favor to explicitly test versions in JavaScript, due to the immense variety of implementations; instead, one should use “feature testing”, executing code to check for the desired behavior. Checking for “abs” as in this task is an example of feature testing.

Testing whether the variable “bloop” exists:

if (typeof bloop !== "undefined") { ... }

The typeof operator explicitly does not throw an error when given an undeclared variable.

Test whether Math.abs() is available:

if ("abs" in Math) { ... }

abs is a method of the Math object, methods are properties, and the in operator tests whether an object has the named property.

[edit] Lasso

var(bloob = -26)
 
decimal(lasso_version(-lassoversion)) < 9.2 ? abort
 
var_defined('bloob') and $bloob -> isa(::integer) and lasso_tagexists('math_abs') ? math_abs($bloob)

-> 26

Lassos equivalence of global variables are thread variables. They have scope that lasts for the entire call in contrast to local variables that are confined to the page or method they are created within.

var(
bloob = -26,
positive = 450
)
 
local(total = integer)
 
with v in var_keys
// Lasso creates a number of thread variables that all start with an underscore. We don't want those
where not(string(#v) -> beginswith('_')) and var(#v) -> isa(::integer)
do {
#total += var(#v)
}
 
#total

-> 424

[edit] Locomotive Basic

To get the BASIC ROM version number, we need to use a Z80 machine code routine which copies the version number (major/minor/patchlevel) to RAM where BASIC can then read it. Here is the assembly:

org &4000   ; program start address
 
push bc
push de
push hl
push af
ld bc,&df00 ; select BASIC ROM
out (c),c ; (ROM 0)
 
ld bc,&7f86 ; make ROM accessible at &c000
out (c),c ; (RAM block 3)
 
ld hl,&c001 ; copy ROM version number to RAM
ld de,&4040
ld bc,3
ldir
 
ld bc,&7f8e ; turn off ROM
out (c),c
pop af
pop hl
pop de
pop bc
ret

The following BASIC program POKEs that routine into memory and quits prematurely if BASIC 1.0 is detected (meaning the machine is a CPC464), as opposed to the more standard 1.1 or later:

10 s=&4000:SYMBOL AFTER 256:MEMORY s-1
20 FOR i=0 to 34:READ a:POKE s+i,a:NEXT
30 DATA &c5,&d5,&e5,&f5,&01,&00,&df,&ed,&49,&01,&86,&7f,&ed,&49
40 DATA &21,&01,&c0,&11,&40,&40,&01,&03,&00,&ed,&b0
50 DATA &01,&8e,&7f,&ed,&49,&f1,&e1,&d1,&c1,&c9
60 CALL s
70 PRINT "BASIC ROM version is ";PEEK(&4040);".";PEEK(&4041);".";PEEK(&4042)
80 IF PEEK(&4041)=0 THEN PRINT "Uh oh, you are still using BASIC 1.0":END
90 PRINT "You are using BASIC 1.1 or later, program can continue"

The second subtask, testing for the presence of a variable, is done here by trying to get the memory address of the variable. If that fails, it is obviously is not yet defined:

1 ' decide randomly whether to define the variable:
10 IF RND>.5 THEN bloop=-100*RND
20 ON ERROR GOTO 100
30 a=@bloop ' try to get a pointer
40 PRINT "Variable bloop exists and its value is",bloop
50 PRINT "ABS of bloop is",ABS(bloop)
90 END
100 IF ERL=30 THEN PRINT "Variable bloop not defined":RESUME 90

(Like the Spectrum version, we have omitted checking for ABS because it is a builit-in function of the BASIC interpreter and therefore always present.)

Extra credit: Finally, we can traverse the memory area where BASIC stores its integer, real, and string variables and add together all integers (type 1):

10 ' The program should find and add those three integers (%), ignoring reals:
20 foo%=-4:bar%=7:baz%=9:somereal=3.141
30 varstart=&ae68 ' for CPC 664 and 6128
40 ' varstart=&ae85 ' (use this line instead on the CPC 464)
50 start=PEEK(varstart)+256*PEEK(varstart+1)
60 WHILE start<HIMEM
70 j=2:WHILE j<43 ' skip variable name
80 IF PEEK(start+j)=0 GOTO 170
90 IF PEEK(start+j)>127 THEN ptr=start+j+1:j=100
100 j=j+1:WEND
110 vartype=PEEK(ptr) ' integer=1, string=2, real=4
120 IF vartype=1 THEN sum=sum+UNT(PEEK(ptr+1)+256*PEEK(ptr+2)):num=num+1:nvar=ptr+3
130 IF vartype=2 THEN nvar=ptr+4
140 IF vartype=4 THEN nvar=ptr+6
150 start=nvar
160 WEND
170 PRINT "There are"num"integer variables."
180 PRINT "Their sum is"sum

Output:

There are 3 integer variables.
Their sum is 12

[edit]

Works with: UCB Logo
show logoversion   ; 5.6
if logoversion < 6.0 [print [too old!]]
 
if and [name? "a] [number? :a] [
print ifelse procedure? "abs [abs :a] [ifelse :a < 0 [minus :a] [:a]]
]

[edit] Logtalk

 
:- object(my_application).
 
:- initialization((
check_logtalk_version,
compute_predicate_if_available
)).
 
check_logtalk_version :-
% version data is available by consulting the "version_data" flag
current_logtalk_flag(version_data, logtalk(Major,Minor,Patch,_)),
( (Major,Minor,Patch) @< (3,0,0) ->
write('Logtalk version is too old! Please upgrade to version 3.0.0 or later'), nl,
halt
; true
).
 
% Logtalk is not a functional language and thus doesn't support user-defined functions; we
% use instead a predicate, abs/2, with a return argument to implement the abs/1 function
compute_predicate_if_available :-
( % check that the variable "bloop" is defined within this object
current_predicate(bloop/1),
% assume that the abs/2 predicate, if available, comes from a "utilities" object
utilities::current_predicate(abs/2) ->
bloop(Value),
utilities::abs(Value, Result),
write('Function value: '), write(Result), nl
; write('Could not compute function!'), nl
).
 
% our "bloop" variable value as per task description
bloop(-1).
 
:- end_object.
 

[edit] Lua

if _VERSION:sub(5) + 0 < 5.1 then print"too old" end --_VERSION is "Lua <version>".
 
if bloop and math.abs then print(math.abs(bloop)) end

[edit] Maple

The "version" kernel option returns a string similar to

> kernelopts( 'version' );
Maple 16.00, SUN SPARC SOLARIS, Mar 3 2012, Build ID 732982

The following does the trick for the first bit.

> if sscanf( (StringTools:-Split(kernelopts(version))[2]), "%d.%d" )[1] < 300 then `quit`(1) end;

(There is also an internal "version" procedure, which returns a build ID, but this is less obvious to use, as you'd need a table mapping versions to build IDs. Besides, it prints stuff.)

It doesn't really make sense to ask whether a variable "exists"; it springs into existence by uttering it in code. So I'll interpret the problem as asking whether it is assigned some kind of numeric value to which abs() can be applied.

> if type( bloop, complex( extended_numeric ) ) and type( abs, mathfunc ) then print( abs( bloop ) ) end:
1/2
13

Note that it is not necessary to check that the name "bloop" is assigned (though it is possible to do so), since an unassigned name is a first-class value in Maple. Another possible interpretation is that the symbolic expression

> abs( bloop );
| bloop |

is a perfectly good expression in Maple, so checking for the the "existence" of "bloop" isn't necessary in the first place. (One probably would not bother to check that abs() was actually there either, unless one expected that the standard library was broken.)

Here are the number and sum of the assigned integer globals in my current (fresh) session.

> nops([anames](integer));
3
 
> eval(`+`(anames(integer)));
17
 

If I change it, I get:

 
> foo := 25:
> nops([anames](integer));
4
 
> eval(`+`(anames(integer)));
42

[edit] Mathematica

If[$VersionNumber  < 8,  Quit[]]
If[NameQ["bloop"] && NameQ["Abs"],
Print[Abs[bloop]]]

Output:

7
globalintegers = Symbol /@ Select[Names["Global`*"], IntegerQ[Symbol[#]] &];
Print [ globalintegers //Length, " global integer(s) and their sum is: ", globalintegers // Total]

Output:

2 global integer(s) and their sum is: 9

[edit] MATLAB / Octave

   % convert version into numerical value
v = version;
v(v=='.')=' ';
v = str2num(v);
if v(2)>10; v(2) = v(2)/10; end;
ver = v(1)+v(2)/10;
if exist('OCTAVE_VERSION','builtin')
if ver < 3.0,
exit
end;
else
if ver < 7.0,
exit
end;
end
 
% test variable bloob, and test whether function abs is defined as m-function, mex-function or builtin-function
if exist('bloob','var') && any(exist('abs')==[2,3,5])
printf('abs(bloob) is %f\n',abs(bloob));
return;
end;

Extra credit task:

 
% find all integers
varlist = whos;
ix = [strmatch('int', {varlist.class}),strmatch('uint', {varlist.class})];
intsumall = 0;
intsum = 0;
for k=1:length(ix)
if prod(varlist(ix).size)==1,
intsum = intsum + eval(varlist.name); % sum only integer scalars
elseif prod(varlist(ix).size)>=1,
tmp = eval(varlist.name);
intsumall = intsumall + sum(tmp(:)); % sum all elements of integer array.
end;
end;
printf('sum of integer scalars: %i\n',intsum);
printf('sum of all integer elements: %i\n',intsumall);
 

[edit] Maxima

/* Get version information */
build_info();
/* build_info("5.27.0", "2012-05-08 11:27:57", "i686-pc-mingw32", "GNU Common Lisp (GCL)", "GCL 2.6.8") */
 
%@lisp_version;
/* "GCL 2.6.8" */
 
/* One can only check for user-defined objects: functions, variables, macros, ...
Hence we won't check for 'abs, which is built-in, but for 'weekday, defined elsewhere on RosettaCode.
Here year, month and day are 2012, 05, 29. */
 
if subsetp({'year, 'month, 'day}, setify(values))
and member('weekday, map(op, functions))
then weekday(year, month, day)
else 'bad\ luck;
 
/* Sum of integer variables */
lreduce("+", sublist(map(ev, values), integerp));

[edit] MAXScript

fn computeAbsBloop bloop =
(
versionNumber = maxVersion()
 
if versionNumber[1] < 9000 then
(
print "Max version 9 required"
return false
)
 
if bloop == undefined then
(
print "Bloop is undefined"
return false
)
 
try
(
abs bloop
)
catch
(
print "No function abs"
false
)
)
 
computeAbsBloop -17

[edit] NetRexx

Like Java, NetRexx will not successfully compile if a program if a variable or method is accessed before it has been defined.

The language does however return a string identifying the version of NetRexx in effect when the current class was last processed. This information can be retrieved through the version special variable.

/* NetRexx */
options replace format comments java crossref symbols binary
 
runSample(arg)
return
 
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
method runSample(arg) private static
parse arg minVersion .
if minVersion = '' then minVersion = 2.0
parse version lang ver bdate
if ver < minVersion then do
say -
lang 'version' ver -
'[Build date:' bdate']' -
'is less than' minVersion.format(null, 2)'; exiting...'
exit
end
else do
say -
lang 'version' ver -
'[Build date:' bdate']' -
'meets minimum requirements of' minVersion.format(null, 2)
end
return
 
Output:
$ java RIntrospection
NetRexx version 3.02 [Build date: 25 Jun 2013] meets minimum requirements of 2.00

$ java RIntrospection 4
NetRexx version 3.02 [Build date: 25 Jun 2013] is less than 4.00; exiting...

[edit] Nimrod

echo NimrodVersion
 
var bloop = -12
 
when compiles abs(bloop):
echo abs(bloop)

Output:

0.9.5
12

[edit] OCaml

# Sys.ocaml_version;;
- : string = "3.10.2"
# Scanf.sscanf (Sys.ocaml_version) "%d.%d.%d"
(fun major minor micro -> major, minor, micro) ;;
- : int * int * int = (3, 10, 2)

Checking if an identifier (a value or a function) is bound doesn't make any sens in OCaml, which is strongly staticaly typed.

For optionnal values we would rather use a structure to contain them, for example an association lists for a small amount of items, or an hash table for a huge amount of data. Both can contain expressions or functions.

[edit] Oz

We cannot check whether a variable is in scope (static property). We can check whether a module exports a certain value. However, for system modules the compiler will refuse to compile if we try to use a non-existing value.

declare
Version = {Property.get 'oz.version'}
%% Version is an atom like '1.4.0'. So we can not compare it directly.
%% Extract the version components:
[Major Minor Release] = {Map {String.tokens {Atom.toString Version} &.} String.toInt}
in
if Major >= 1 andthen Minor >= 4 then
%% check whether module Number exports a value 'abs':
if {HasFeature Number abs} then
{Show {Number.abs ~42}}
end
else
{System.showInfo "Your Mozart version is too old."}
end

[edit] PARI/GP

Works with: PARI/GP version 2.4.3 and above
if(lex(version(), [2,4,3]) < 0, quit()); \\ Compare the version to 2.4.3 lexicographically
 
if(bloop!='bloop && type(abs) == "t_CLOSURE", abs(bloop))

[edit] Perl

Works with: Perl version 5.x
require v5.6.1;    # run time version check
require 5.6.1; # ditto
require 5.006_001; # ditto; preferred for backwards compatibility

To check if a variable exists, do a name lookup of it in the package symbol table:

#$bloop = -123;   # uncomment this line to see the difference
no strict 'refs'; # referring to variable by name goes against 'strict' pragma
if (defined($::{'bloop'})) {print abs(${'bloop'})} else {print "bloop isn't defined"};

To check if certain built-in function is available (maybe you are using a stripped down build of perl binary, for example), one can use eval, but make sure the statement you are eval'ing doesn't have side effect:

eval('abs(0)');  # eval("") instead of eval{}; the latter is not for run-time check
print "abs() doesn't seem to be available\n" if $@;

But the following would be a bad idea, so be careful:

eval('system("rm -rf /")');
print "system() doesn't seem to be available\n" if $@;

To check if a package or object provides certain method name, use 'can':

use Math::Complex;
my $cpl = Math::Complex->new(1,1);
 
print "package Math::Complex has 'make' method\n"
if Math::Complex->can('make');
 
print "object \$cpl does not have 'explode' method\n"
unless $cpl->can('explode');
 

Keep in mind that what a package has as method names are not equal to what method names can be called on this package, due to things like AUTOLOAD. For most uses, introspection is meaningless, just call the method (and catch exceptions if it's important).

An example that solves the task:

use 5.010;
our $bloop = -12;
if (defined $::bloop) {
if (eval { abs(1) }) {
say 'abs($bloop) is ' . abs($::bloop);
}
else {
say 'abs() is not available';
}
}
else {
say '$bloop is not defined';
}

Note that this program will exit with a message "Perl v5.10.0 required" if run under perl version lower than 5.10 and it actually uses a feature introduced in that version (say). The program checks whether the variable is actually defined and not if it just exists. In Perl a variable can exist and have an undefined value, and checking for existence is problematic because many read-only operations may create an empty slot in the global namespace as a side effect. It doesn't make sense to calculate absolute values of existent but undefined variables so it doesn't matter in this task. It can be tested by commenting out the our $bloop line. The existence of abs() function is tested using eval that returns false if the abs(1) cannot be invoked which can be tested by changing the name of the function in the eval test.

Extra task:

use 5.010;
package test;
use Regexp::Common;
use List::Util qw(sum);
 
our $a = 7;
our $b = 1;
our $c = 2;
our $d = -5;
our $e = 'text';
our $f = 0.25;
 
my @ints = grep { /^$RE{num}{int}$/ } map { $$_ // '' } values %::test::;
my $num = @ints;
my $sum = sum @ints;
say "$num integers, sum = $sum";

It prints:

4 integers, sum = 5

This example uses the test namespace instead of the default, because there already are some integer numbers in the main namespace like the PID, etc. The program to sum those numbers would be:

use 5.010;
use Regexp::Common;
use List::Util qw(sum);
my @ints = grep { /^$RE{num}{int}$/ } map { $$_ // '' } values %::;
my $num = @ints;
my $sum = sum @ints;
say "$num integers, sum = $sum";
4 integers, sum = 74717

[edit] Perl 6

use v6.0;   # require Perl 6.0
 
my $bloop = -123;
 
if MY::{'$bloop'}.defined and CORE::{'&abs'}.defined { say abs $bloop }
 
my @ints = ($_ when Int for PROCESS::.values);
say "Number of PROCESS vars of type Int: ", +@ints;
say "PROCESS vars of type Int add up to ", [+] @ints;
Output:
123
Number of PROCESS vars of type Int: 1
PROCESS vars of type Int add up to 28785

Obviously Perl 6 doesn't maintain a lot of global integer variables... :-)

Nevertheless, you can use similar code to access all the variables in any package you like, such as the GLOBAL package, which typically has absolutely nothing in it. Since the PROCESS package is even more global than GLOBAL, we used that instead. Go figure...

[edit] PHP

<?php
 
if (version_compare(PHP_VERSION, '5.3.0', '<' ))
{
echo("You are using PHP Version " . PHP_VERSION . ". Please upgrade to Version 5.3.0\n");
exit();
}
$bloop = -3;
if (isset($bloop) && function_exists('abs'))
{
echo(abs($bloop));
}
echo(count($GLOBALS) . " variables in global scope.\n");
echo(array_sum($GLOBALS) . " is the total of variables in global scope.\n");
 
?>

[edit] PicoLisp

(unless (>= (version T) (3 0 1))       # Check version (only in the 64-bit version)
(bye) )
 
# (setq bloop -7) # Uncomment this to get the output '7'
 
(and
(num? bloop) # When 'bloop' is bound to a number
(getd 'abs) # and 'abs' defined as a function
(println (abs bloop)) ) # then print the absolute value

[edit] PL/I

[edit] Version 1

 
S = SYSVERSION();
if substr(S, 6, 6) < '050000' then
do; put skip list ('Version of compiler is too old'); stop; end;
 

[edit] Version 2

*process source attributes options m or(!);
/*********************************************************************
* 02-11.2013 Walter Pachl
* I modified this to run on my Windows PL/I
*********************************************************************/
v: Proc Options(main);
 %version: Proc Returns(char);
Dcl res char;
res=sysversion;
Return(''''!!res!!'''');
 %End;
 %Act version;
Dcl s char(31) Init('');
s=version;
if substr(S,15,3) < '7.5' then Do;
put Skip list('Version of compiler ('!!substr(S,15,3)!!
') is too old');
stop;
End;
Else
Put Skip List('Version is '!!s);
End

Output:

Version is PL/I for Win* 7.5

[edit] Pop11

Variable pop_internal_version contains Poplog version in numeric form (as an integer) -- this one is most convenient for version checks. For printing one can use pop_version (which is a string containing more information).

;;; Exit if version below 15.00
if pop_internal_version < 150000 then
sysexit()
endif;

Pop11 variables are named by words. Pop11 word is a unique version of string stored in dictionary. So we need first convert strings to words and then query about words. Pop11 variables can store any value including functions and in fact when one accesses a function like abs by name one merely access a variable abs which happen to hold predefined function abs. To follow spirit of the task as closely as possible we check if abs indeed holds functional value.

;;; We do main task in a procedure
define check_and_call(x, y);
lvars wx=consword(x), wy=consword(y);
if identprops(wx) = 0 and isprocedure(valof(wx))
and identprops(wy) = 0 then
return(valof(wx)(valof(wy)));
else
return("failed");
endif;
enddefine;
 
;;; Prints failed because bloop is undefined
check_and_call('abs' , 'bloop') =>
;;; Define bloop
vars bloop = -5;
;;; Now prints 5
check_and_call('abs' , 'bloop') =>

Note that here bloop is defined as "permanent" variable, Pop11 also have lexical variables which are not available for introspection.

[edit] PowerBASIC

PowerBASIC has no way of determining if a variable "exists" in code. If variable declaration is required (using #DIM ALL), then any attempt to use a variable without declaring it will result in a failed compile; if variable declaration is not required, then the first time the program accesses the variable it is automatically created with the default data type (which is set using DEFtype).

The compiler directive #COMPILER, introduced with PB/Win 8 and PB/CC 4, will fail the compile if the compiler does not match at least one of the listed comilers, and is not at least the (optional) minimum version of that compiler.

#COMPILER PBWIN 9
#COMPILER PBWIN, PBCC 5

[edit] PowerShell

# version is found in $PSVersionTable
if ($PSVersionTable['PSVersion'] -lt '2.0') {
exit
}
 
if ((Test-Path Variable:bloop) -and ([Math]::Abs)) {
[Math]::Abs($bloop)
}
 
# find integer variables and their sum
Get-Variable -Scope global `
| Where-Object { $_.Value -is [int] } `
| Measure-Object -Sum Value `
| Select-Object Count,Sum

[edit] PureBasic

CompilerIf #PB_Compiler_Version<441
CompilerError "You failed the version check!"
CompilerEndIf
 
CompilerIf Defined(bloop,#PB_Variable)
CompilerIf Defined(Abs(),#PB_Function)
Abs(bloop)
CompilerEndIf
CompilerEndIf

[edit] Python

# Checking for system version
import sys
major, minor, bugfix = sys.version_info[:3]
if major < 2:
sys.exit('Python 2 is required')
 
 
def defined(name): # LBYL (Look Before You Leap)
return name in globals() or name in locals() or name in vars(__builtins__)
 
def defined2(name): # EAFP (Easier to Ask Forgiveness than Permission)
try:
eval(name)
return True
except NameError:
return False
 
if defined('bloop') and defined('abs') and callable(abs):
print abs(bloop)
 
if defined2('bloop') and defined2('abs') and callable(abs):
print abs(bloop)

You can combine both tests, (But loose sight of which variable in missing/not callable by wrapping the whole function call in a try-except statement:

try:
print abs(bloop)
except (NameError, TypeError):
print "Something's missing"

Here is one way to print the sum of all the global integer variables:

def sum_of_global_int_vars():
variables = vars(__builtins__).copy()
variables.update(globals())
print sum(v for v in variables.itervalues() if type(v) == int)
 
sum_of_global_int_vars()

[edit] R

Works with: R version 2.14.1
 
if(getRversion() < "2.14.1")
{
warning("Your version of R is older than 2.14.1")
q() # exit R, with the option to cancel
}

The constants version and R.version give further information about the version that is running. The function R.Version() provides the same information as a list.

We now perform three checks: we want to know if bloop is in the user workspace (global environment), if abs exists somewhere, and if abs is a function.

bloop <- -3.4
if(exists("bloop", envir=globalenv()) && exists("abs") && is.function(abs))
{
abs(bloop)
}

Finally, we count how many integers are in the user workspace, and find their total. Note that a number followed by the letter L is considered to be an integer. See Integer_literals#R for more information.

#Declare some integers
qqq <- 45L
www <- -3L
#Retrieve the name of all the variables in the user workspace
var_names <- ls()
#Retrieve the actual variables as a list
all_vars <- mget(var_names, globalenv())
#See which ones are integers
is_int <- sapply(all_vars, is.integer)
#Count them
sum(is_int)
#Retrieve the variables that were integers
the_ints <- mget(varnames[is_int], globalenv())
#Add them up
sum(unlist(the_ints))

[edit] Racket

The usual hack:

 
#lang racket
(unless (string<=? "5.3" (version)) (error "ancient version"))
 

Proper comparison:

 
(require version/utils)
(unless (version<=? "5.3" (version)) (error "ancient version"))
 

[edit] Raven

VERSION 0 prefer 20071104 <
if 'version >= 20071104 required' print bye
 
'bloop' GLOBAL keys in && 'abs' CORE keys in
if bloop abs print


[edit] Retro

This will exit if the minor version is less than 3:

version ^strings'splitAtChar: . drop toNumber 3 < &bye ifTrue

A better way is to check the build number. This will exit if the build is lower than the 11.0 release:

build toNumber 1309798464 < &bye ifTrue

The existance of functions can be checked using find. In this, a helper function is provided to improve readability.

 
( Checks for existance of "bloop" and "abs" )
: executeByName ( $- )
find drop [ @d->xt ] [ @d->class ] bi withClass ;
 
"bloop" "abs" [ find nip ] bi@ and
[ "bloop" executeByName "abs" executeByName ] ifTrue

Retro has no direct way to check for data types of functions. Assuming that a word class is defined for integer variables, we could do something like this:

 
0 0 last [ dup @d->class &.integer = [ @d->xt @ + [ 1+ ] dip ] [ drop ] if ] ^types'LIST each@
 

After execution the stack will have the number of variables found, and the accumulated sum of their values.

[edit] REXX

Test to see if the version is at least version 4.

           /*output from parse version (almost all REXX versions)  */
/* theREXXinterpreterName level mm Mon yyyy */
 
parse version . level .
if level<4 then exit

Test to see if the version is at least version 4, another example.

parse version x 1 whatLang level mm mon yyyy .
if level<4 then do
say
say 'version' level "is too old!"
say x /*this displays everything.*/
exit /*or maybe: EXIT 13 */
end

Test to see if the REXX variable "bloop" exists, version 1.

if symbol('bloop')=='VAR' then say 'the "bloop" variable exists.'

Test to see if the REXX variable "bloop" exists, version 2.

if symbol('bloop')=='VAR' then say 'the "bloop" variable exists.'
else say 'the "bloop" variable doesn''t exist.'

Another test to see if the REXX variable "bloop" exists.

bloop=47
if symbol('bloop')=='VAR' then say 'the "bloop" variable exists.'
else say 'the "bloop" variable doesn''t exist.'

In REXX, the ABS function is a built-in function (BIF).

bloop=47
g=abs(bloop)

However, most REXX interpretors will allow this type of test:

if testxyz() then say 'function XYZ not found.'
else say 'function XYZ was found.'
exit
 
testxyz: signal on syntax
call XYZ
return 0
 
syntax: return 1

[edit] Ruby

exit if RUBY_VERSION < '1.8.6'
puts bloop.abs if defined?(bloop) and bloop.respond_to?(:abs)

Extra credit:

def variable_counter(b)
int_vars = []
sum = 0
check_var = lambda do |name, value|
if value.is_a?(Integer)
int_vars << name
sum += value
end
end
 
Kernel.global_variables.each {|varname| check_var.call(varname, eval(varname))}
eval('local_variables', b).each {|varname| check_var.call(varname, eval(varname, b))}
 
puts "these #{int_vars.length} variables in the global scope are integers:"
puts int_vars.inspect
puts "their sum is: #{sum}"
end
 
an_int = 5
a_string = 'foo'
a_float = 3.14
 
variable_counter(binding)

Output:

these 4 variables in the global scope are integers:
["$$", "$.", "$SAFE", "an_int"]
their sum is: 3239

The meaning of these variables can be found many places, including here.

[edit] Scala

object VersCheck extends App {
val minimalVersion = 1.7
 
val vers = System.getProperty("java.specification.version");
println(if (vers.toDouble >= minimalVersion) "YAY!" else s"Must use Java >= $minimalVersion");
 
val bloop = Option(-42)
if (bloop.isDefined) bloop.get.abs
}

[edit] Slate

No version string included inside the system presently.

Platform run: StartupArguments first ; ' --version'.
(lobby hasSlotNamed: #bloop) /\ [(#abs findOn: {lobby bloop}) isNotNil] ifTrue: [inform: bloop abs printString].
lobby slotValues inject: 0 into: [| :sum :value | (value is: Integer) ifTrue: [sum + value] ifFalse: [sum]].

[edit] Smalltalk

Works with: GNU Smalltalk
| s v t sum hm |
"uncomment the following to see what happens if bloop exists"
"Smalltalk at: #bloop put: -10."
s := Smalltalk version.
(s =~ '(\d+)\.(\d+)\.(\d+)')
ifMatched: [:match |
v := (( (match at: 1) asInteger ) * 100) +
(( (match at: 2) asInteger ) * 10) +
( (match at: 3) asInteger )
].
( v < 300 )
ifTrue: [
Transcript show: 'I need version 3.0.0 or later' ; cr ]
ifFalse: [
Transcript show: 'Ok! I can run!' ; cr .
"does bloop exists as global var?"
t := Smalltalk at: #bloop
ifAbsent: [
Transcript show: 'bloop var does not exist as global!' ; cr .
^nil
].
(t respondsTo: #abs)
ifTrue:
[ Transcript show: 'Absolute value of bloop: ' ;
show: (t abs) printString ; cr ].
] .
 
"how many 'numbers' in global scope, and compute their sums"
hm := 0.
sum := 0.
(Smalltalk keys) do: [ :els |
( (Smalltalk at: els) isKindOf: Number )
ifTrue: [ hm := hm + 1.
sum := sum + (Smalltalk at: els).
"Transcript show: (els asString) ; cr" ]
] .
Transcript show: 'Num of global numeric vars: '; show: (hm printString); cr ;
show: 'Sum of global numeric vars: '; show: (sum printString) ; cr.

[edit] Tcl

package require Tcl 8.4 ; # throws an error if older
if {[info exists bloop] && [llength [info functions abs]]} {
puts [expr abs($bloop)]
}

Extra credit:

namespace eval ::extra_credit {
variable sum_global_int 0
variable n_global_int 0
foreach var [info vars ::*] {
if {[array exists $var]} continue
if {[string is int -strict [set $var]]} {
puts "$var = [set $var]"
incr sum_global_int [set $var]
incr n_global_int
}
}
puts "number of global ints = $n_global_int"
puts "their sum = $sum_global_int"
}

[edit] TI-89 BASIC

()
Prgm
Local l, i, vers
getConfg() → l
For i,1,dim(l),2
If l[i] = "OS Version" or l[i] = "Version" Then
l[i + 1] → vers
Disp "Version: " & vers
If expr(right(vers, 4)) < 2005 Then © Lousy parsing strategy
Disp vers & " is too old"
Stop
EndIf
EndIf
EndFor
 
If isVar(bloop) Then © Dynamic name check can be done with isVar(#aString)
© Builtin functions cannot be tested for.
Disp abs(bloop)
Else
Disp "No bloop"
EndIf
 
© There is no way to get a list of global variables.
EndPrgm

[edit] Toka

Works with: Toka version 1.1+

Starting with Release 1.1, Toka allows for checking the version number:

VERSION 101 > [ bye ] ifFalse

Release 1.0 can be detected by doing:

` VERSION FALSE = [ bye ] ifTrue

Basic introspection is possible via `

` bloop FALSE <> ` abs FALSE <> and [ ` bloop invoke @ ` abs invoke ] ifTrue

[edit] UNIX Shell

Works with: ksh93

There's no way to introspect the builtin arithmetic functions. We'll just try it and see if there's an error.

case ${.sh.version} in
*93[[:alpha:]]+*) :;; #this appears to be ksh93, we're OK
*) echo "version appears to be too old"
exit # otherwise, bail out
;;
esac
 
if [[ -z ${bloop+bloop has a value} ]]; then
print "no bloop variable"
elsif (( abs(1) )); then
print -- $(( abs(bloop) ))
fi
 
typeset -a int_vars
set | while IFS='=' read -r var value; do
if [[ $value == +([[:digit:]]) ]]; then
int_vars[n++]=$var
let sum += $value
fi
done
print "${int_vars[*]}"
print -- $sum
Works with: bash

bash does not have a builtin math function "abs" -- we'll check for a user-defined shell function instead.

if [[ $BASH_VERSION < "4.2" ]]; then
echo "version is too old"
exit
fi
 
if [[ ! -v bloop ]]; then
echo "no bloop variable"
elif [[ $(type -t abs 2>/dev/null) != function ]]; then
echo "abs is not a shell function"
else
echo $(abs $bloop)
fi
 
# need to populate the variables and use them within the same subshell in a pipeline.
set | {
shopt -s extglob
int_vars=()
while IFS='=' read -r var value; do
if [[ $value == +([[:digit:]]) ]]; then
int_vars+=($var)
(( sum += value ))
fi
done
echo "${int_vars[*]}"
echo $sum
}

[edit] Ursala

When the user defined function maybe_abs(x) is evaluated, a run time check is performed for the availability of the system library's absolute value function (fabs), and if found, it is used. If not, the function tries to invoke a replacement function named 'abs' from the imported floating point function library, flo. (The search for a replacement is performed at the time maybe_abs is compiled, and is possible because any imported library is presented as a list of (identifier:value) pairs.) If no imported absolute value function is available either, maybe_abs returns a copy of the argument x unchanged.

The #preprocess directive allows arbitrary user defined transformations to be applied to the abstract syntax trees created by the compiler (assuming a knowledge of the compiler internals). This example of a preprocessor aborts compilation if the run time system version differs from 0.10.2. Otherwise, a search is performed for any declared symbol named 'bloop' whose evaluation has been resolved, and its value is replaced with the absolute value as given by maybe_abs.

On platforms where at least one of the absolute value functions is available, the -1. shown in the source text will have been changed to 1 by the time it's displayed.

#import std
#import flo
#import lag
 
maybe_abs = math.|fabs (%QI flo)-:~&! 'abs'
 
#preprocess version==-[0.10.2]-?\<'wrong version'>!% *^0 ||~& -&
-&~&vitB,~&d.lexeme=='=',~&vhd.lexeme=='bloop',~&vthd.lexeme=='(evaluated)'&-,
&vthd.semantics:= !+ !+ maybe_abs+ ~&vthd.semantics.&iNHiNH&-
 
#cast %e
 
bloop = -1.

output:

1.000000e+00

[edit] VBA

Under VBA (and most, if not all, variations of Visual Basic), accessing an undeclared variable will automatically create it as a Variant, unless declaration is required (via Option Explicit), in which case a compile-time error is generated and the compile fails (or in the case of interpreted varieties, the code will not run).

To determine the version of the environment -- typically meaning which version of Microsoft Office is running -- the Application object has a Version property:

If Application.Version < 15 Then Exit Sub

[edit] zkl

Language.version //-->L(1,12,8,"2014-04-01")
if (Language.version[1] < 10) System.exit("Too old");
var bloop=-123;
if ((1).resolve("abs",1) and resolve("bloop",8)) bloop.abs().println()
Output:
123

The concept of global vars doesn't really exist, only instance data.

var n=3, x=1.0, a=5, z="zoo";
self.vars; --> L(L("a",5),L("n",3),L("x",1),L("z","zoo"))
sum:=self.vars.reduce(fcn(p,[(nm,v)],r){
if((1).isType(v)){r.inc();p+v;} else p},0,num:=Ref(0));
println("Num int vars = ",num.value,". Sum = ",sum);
Output:
Num int vars = 2. Sum = 8

[edit] ZX Spectrum Basic

10 LET totram=PEEK 23732 + 256 * PEEK 23733: REM Check that we have a 48k machine
20 IF totram < 65535 THEN PRINT "Your 16k Spectrum is too old": STOP
30 REM variables must exist before they are used, otherwise we get an error
40 REM we can poke a new error handler and check for variable not found.
50 REM I haven't implemented this, because I have forgotten the handler address
60 LET bloob = -4: REM make sure bloob exists, by creating it.
70 PRINT ABS(bloob): REM function will be present, ZX Spectrum Basic is standardized.
Personal tools
Namespaces

Variants
Actions
Community
Explore
Misc
Toolbox