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Optional parameters

From Rosetta Code
Optional parameters
You are encouraged to solve this task according to the task description, using any language you may know.

Define a function/method/subroutine which sorts a sequence ("table") of sequences ("rows") of strings ("cells"), by one of the strings. Besides the input to be sorted, it shall have the following optional parameters:

A function specifying the ordering of strings; lexicographic by default.
An integer specifying which string of each row to compare; the first by default.
Reverses the ordering.

This task should be considered to include both positional and named optional parameters, as well as overloading on argument count as in Java or selector name as in Smalltalk, or, in the extreme, using different function names. Provide these variations of sorting in whatever way is most natural to your language. If the language supports both methods naturally, you are encouraged to describe both.

Do not implement a sorting algorithm; this task is about the interface. If you can't use a built-in sort routine, just omit the implementation (with a comment).

See also:


As described in Named_parameters, all parameters have to be named. You can use positional or keyed association. Optional parameters are the ones with default values.

package Tables is
type Table is private;
type Ordering is (Lexicographic, Psionic, ...); -- add others
procedure Sort (It  : in out Table;
Order_By  : in Ordering := Lexicographic;
Column  : in Positive := 1;
Reverse_Ordering : in Boolean  := False);
... -- implementation specific
end Tables;

example of use:

with Tables;
procedure Table_Test is
My_Table : Tables.Table;
... -- insert stuff in table
Sort (My_Table); -- use default sorting
Sort (My_Table, Psionic, 5, True); -- use psionic sorting by 5th column in reverse order
Sort (It => My_Table, Reverse_Ordering => True); -- use default sorting in reverse order
... -- other stuff
end Table_Test;

ALGOL 68[edit]

# as the options have distinct types (INT, BOOL and PROC( STRING, STRING )INT) the       #
# easiest way to support these optional parameters in Algol 68 would be to have an array #
# with elements of these types #
# See the Named Arguments sample for cases where the option types are not distinct #
# default comparison function #
PROC default compare = ( STRING a, b )INT: IF a < b THEN -1 ELIF a = b THEN 0 ELSE 1 FI;
# sorting procedure #
PROC configurable sort = ( [,]STRING data, []UNION( INT, BOOL, PROC( STRING, STRING )INT ) options )VOID:
# set initial values for the options #
INT sort column := 2 LWB data;
BOOL reverse sort := FALSE;
PROC( STRING, STRING )INT comparator := default compare;
# overide from the supplied options #
FOR opt pos FROM LWB options TO UPB options DO
CASE options[ opt pos ]
IN ( PROC( STRING, STRING )INT p ): comparator := p
, ( INT c ): sort column := c
, ( BOOL r ): reverse sort := r
# do the sort .... #
END # configurable sort # ;
# example calls #
[ 1 : 2, 1 : 3 ]STRING data := ( ( "a", "bb", "cde" ), ( "x", "abcdef", "Q" ) );
# sort data, default comparison, first column, reverse order #
configurable sort( data, ( TRUE ) );
# sort data, second column, ignore first chaacter when sorting, normal order #
configurable sort( data, ( 2, ( STRING a, STRING b )INT: default compare( a[ LWB a + 1 : ], b[ LWB b + 1 : ] ) ) );
# default sort #
configurable sort( data, () )


AppleScript supports named, positional & prepositional parameters, but not default or optional parameters. Though that behavior can be simulated by passing lists or records as the parameter. Handler/functions can be passed as a parameter if they are part of a script object. AppleScript does not have built-in sorting functionality.

on sortTable(x)
set {sortOrdering, sortColumn, sortReverse} to {sort_lexicographic, 1, false}
set sortOrdering to x's ordering
end try
set sortColumn to x's column
end try
set sortReverse to x's reverse
end try
return sortOrdering's sort(x's sequence, sortColumn, sortReverse)
end sortTable
script sort_lexicographic
on sort(table, column, reverse)
-- Implement lexicographic Sorting process here.
return table
end sort
end script

Examples of use:

-- Another sort function.
script sort_colex
on sort(table, column, reverse)
-- Implement colexicographic Sorting process here.
return table
end sort
end script
-- Populate a table (list) with data.
set table to {{1,2},{3,4}}
sortTable({sequence:table, ordering:sort_lexicographic, column:1, reverse:false})
sortTable({sequence:table, ordering:sort_colex, column:2, reverse:true})
sortTable({sequence:table, reverse:true})


built in support for table sorting is available through the standard Win32 listview.

Gosub start ; create and show the gui
sort_table("Text", column := 2, reverse := 1) ; lexicographic sort
Sleep, 2000
sort_table("Integer", column := 2, reverse := 1) ; numerical sort
Gui, Add, ListView, r20 w200, 1|2|3
data =
Loop, Parse, data, `n
StringSplit, row, A_LoopField, `,
LV_Add(row, row1, row2, row3)
LV_ModifyCol(50) ; Auto-size columns
Gui, Show
; The function supporting named, defaulted arguments
sort_table(ordering = "Text", column = 0, reverse = 0)
If reverse
desc = desc
LV_ModifyCol(column, "sort" . desc . " " . ordering)


Works with: Beta BASIC version 3.0

Works with: SAM BASIC

In Beta BASIC and SAM BASIC, the default values for parameters (or any variable) is given with the keyword DEFAULT.

100 DEF PROC sort_table REF t$(), ordering, col, reverse
110   DEFAULT ordering=0, col=1, reverse=0
120   REM implementation of sort not shown

Usage example:

500 DIM a$(100,80)
510 REM fill a$ with data here...
550 sort_table a$
570 sort_table a$, 1, 5, 1


BBC BASIC doesn't have optional parameters, but functions can have multiple entry points which take different numbers of parameters, avoiding the need to duplicate code or call a sub-function. Omitted parameters can be declared as LOCAL, which initialises them to zero/false.

      DIM table$(100,100)
PROCsort_options(table$(), TRUE, 1, FALSE)
DEF PROCsort_options(table$(), ordering%, column%, reverse%)
DEF PROCsort_default(table$()) : LOCAL ordering%, column%, reverse%
REM The sort goes here, controlled by the options
REM Zero/FALSE values for the options shall select the defaults


Bracmat functions always have exactly one parameter, which is references by !arg in the function body. Positional and (optional) named 'parameters' are retrieved from this single parameter !arg by pattern matching. It is a good custom to separate positional parameters by commas or periods and to separate the named parameters by spaces.

( ( sortTable
= table ordering column reverse
.  !arg
 : ( ?table
. ( ? (ordering.?ordering) ?
| ?&lexicographic:?ordering
 : ( ? (column.?column) ?
| ?&1:?column
 : ( ? (reverse.?reverse) ?
| ?&no:?reverse
& (...)
& (12.Claes.left)
 : ?table
& sortTable$(!table.(column.2) (reverse.yes))


#include <stdlib.h>
#include <stdarg.h>
#include <stdio.h>
#include <ctype.h>
#include <string.h>
typedef const char * String;
typedef struct sTable {
String * *rows;
int n_rows,n_cols;
} *Table;
typedef int (*CompareFctn)(String a, String b);
struct {
CompareFctn compare;
int column;
int reversed;
} sortSpec;
int CmprRows( const void *aa, const void *bb)
String *rA = *(String *const *)aa;
String *rB = *(String *const *)bb;
int sortCol = sortSpec.column;
String left = sortSpec.reversed ? rB[sortCol] : rA[sortCol];
String right = sortSpec.reversed ? rA[sortCol] : rB[sortCol];
return left, right );
/** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* tbl parameter is a table of rows of strings
* argSpec is a string containing zero or more of the letters o,c,r
* if o is present - the corresponding optional argument is a function which
* determines the ordering of the strings.
* if c is present - the corresponding optional argument is an integer that
* specifies the column to sort on.
* if r is present - the corresponding optional argument is either
* true(nonzero) or false(zero) and if true, the sort will b in reverse order
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

int sortTable(Table tbl, const char* argSpec,... )
va_list vl;
const char *p;
int c; = &strcmp;
sortSpec.column = 0;
sortSpec.reversed = 0;
va_start(vl, argSpec);
if (argSpec)
for (p=argSpec; *p; p++) {
switch (*p) {
case 'o': = va_arg(vl,CompareFctn);
case 'c':
c = va_arg(vl,int);
if ( 0<=c && c<tbl->n_cols)
sortSpec.column = c;
case 'r':
sortSpec.reversed = (0!=va_arg(vl,int));
qsort( tbl->rows, tbl->n_rows, sizeof(String *), CmprRows);
return 0;
void printTable( Table tbl, FILE *fout, const char *colFmts[])
int row, col;
for (row=0; row<tbl->n_rows; row++) {
fprintf(fout, " ");
for(col=0; col<tbl->n_cols; col++) {
fprintf(fout, colFmts[col], tbl->rows[row][col]);
fprintf(fout, "\n");
fprintf(fout, "\n");
int ord(char v)
return v-'0';
/* an alternative comparison function */
int cmprStrgs(String s1, String s2)
const char *p1 = s1;
const char *p2 = s2;
const char *mrk1, *mrk2;
while ((tolower(*p1) == tolower(*p2)) && *p1) {
p1++; p2++;
if (isdigit(*p1) && isdigit(*p2)) {
long v1, v2;
if ((*p1 == '0') ||(*p2 == '0')) {
while (p1 > s1) {
p1--; p2--;
if (*p1 != '0') break;
if (!isdigit(*p1)) {
p1++; p2++;
mrk1 = p1; mrk2 = p2;
v1 = 0;
while(isdigit(*p1)) {
v1 = 10*v1+ord(*p1);
v2 = 0;
while(isdigit(*p2)) {
v2 = 10*v2+ord(*p2);
if (v1 == v2)
return v1 - v2;
if (tolower(*p1) != tolower(*p2))
return (tolower(*p1) - tolower(*p2));
for(p1=s1, p2=s2; (*p1 == *p2) && *p1; p1++, p2++);
return (*p1 -*p2);
int main()
const char *colFmts[] = {" %-5.5s"," %-5.5s"," %-9.9s"};
String r1[] = { "a101", "red", "Java" };
String r2[] = { "ab40", "gren", "Smalltalk" };
String r3[] = { "ab9", "blue", "Fortran" };
String r4[] = { "ab09", "ylow", "Python" };
String r5[] = { "ab1a", "blak", "Factor" };
String r6[] = { "ab1b", "brwn", "C Sharp" };
String r7[] = { "Ab1b", "pink", "Ruby" };
String r8[] = { "ab1", "orng", "Scheme" };
String *rows[] = { r1, r2, r3, r4, r5, r6, r7, r8 };
struct sTable table;
table.rows = rows;
table.n_rows = 8;
table.n_cols = 3;
sortTable(&table, "");
printf("sort on col 0, ascending\n");
printTable(&table, stdout, colFmts);
sortTable(&table, "ro", 1, &cmprStrgs);
printf("sort on col 0, reverse.special\n");
printTable(&table, stdout, colFmts);
sortTable(&table, "c", 1);
printf("sort on col 1, ascending\n");
printTable(&table, stdout, colFmts);
sortTable(&table, "cr", 2, 1);
printf("sort on col 2, reverse\n");
printTable(&table, stdout, colFmts);
return 0;


This implementation only accepts function pointers for the comparators, and does not accept function objects, for simplicity.

#include <vector>
#include <algorithm>
#include <string>
// helper comparator that is passed to std::sort()
template <class T>
struct sort_table_functor {
typedef bool (*CompFun)(const T &, const T &);
const CompFun ordering;
const int column;
const bool reverse;
sort_table_functor(CompFun o, int c, bool r) :
ordering(o), column(c), reverse(r) { }
bool operator()(const std::vector<T> &x, const std::vector<T> &y) const {
const T &a = x[column],
&b = y[column];
return reverse ? ordering(b, a)
: ordering(a, b);
// natural-order less-than comparator
template <class T>
bool myLess(const T &x, const T &y) { return x < y; }
// this is the function we call, which takes optional parameters
template <class T>
void sort_table(std::vector<std::vector<T> > &table,
int column = 0, bool reverse = false,
bool (*ordering)(const T &, const T &) = myLess) {
std::sort(table.begin(), table.end(),
sort_table_functor<T>(ordering, column, reverse));
#include <iostream>
// helper function to print our 3x3 matrix
template <class T>
void print_matrix(std::vector<std::vector<T> > &data) {
for () {
for (int j = 0; j < 3; j++)
std::cout << data[i][j] << "\t";
std::cout << std::endl;
// order in descending length
bool desc_len_comparator(const std::string &x, const std::string &y) {
return x.length() > y.length();
int main() {
std::string data_array[3][3] =
{"a", "b", "c"},
{"", "q", "z"},
{"zap", "zip", "Zot"}
std::vector<std::vector<std::string> > data_orig;
for (int i = 0; i < 3; i++) {
std::vector<std::string> row;
for (int j = 0; j < 3; j++)
std::vector<std::vector<std::string> > data = data_orig;
data = data_orig;
sort_table(data, 2);
data = data_orig;
sort_table(data, 1);
data = data_orig;
sort_table(data, 1, true);
data = data_orig;
sort_table(data, 0, false, desc_len_comparator);
return 0;


Translation of: Python
import std.stdio, std.algorithm, std.functional;
string[][] sortTable(string[][] table,
in bool function(string[],string[]) ordering=null,
in int column = 0,
in bool reverse = false) {
if (ordering is null)
table.schwartzSort!(row => row[column])();
if (reverse)
return table;
void main() {
auto data = [["a", "b", "c"],
["", "q", "z"],
["zap", "zip", "Zot"]];
alias show = curry!(writefln, "%-(%s\n%)\n");
show(sortTable(data, null, 2));
show(sortTable(data, null, 1));
show(sortTable(data, null, 1, true));
show(sortTable(data, (a,b) => b.length > a.length));
["a", "b", "c"]
["", "q", "z"]
["zap", "zip", "Zot"]

["", "q", "z"]
["a", "b", "c"]
["zap", "zip", "Zot"]

["zap", "zip", "Zot"]
["a", "b", "c"]
["", "q", "z"]

["a", "b", "c"]
["", "q", "z"]
["zap", "zip", "Zot"]

["zap", "zip", "Zot"]
["", "q", "z"]
["a", "b", "c"]

["zap", "zip", "Zot"]
["", "q", "z"]
["a", "b", "c"]

Another way to emulate optional arguments is with function overloading, creating several functions with a different number of arguments.


There is a built-in sort routine, but rather than figure out what all these arguments are supposed to mean, I've just defined the interface.

(defn sort [table & {:keys [ordering column reverse?]
 :or {ordering :lex, column 1}}]
(println table ordering column reverse?))
(sort [1 8 3] :reverse? true)
[1 8 3] :lex 1 true

Common Lisp[edit]

Common Lisp has both named and positional parameters. The following example shows optional named parameters, using the &key keyword. Optional positional parameters are specified using the &optional keyword.

(defun sort-table (table &key (ordering #'string<)
(column 0)
(sort table (if reverse
(complement ordering)
:key (lambda (row) (elt row column))))

(Notes: The builtin sort takes a "less than" predicate function. The complement function inverts a predicate.)

Example uses:

CL-USER> (defparameter *data* '(("a" "b" "c") ("" "q" "z") ("zap" "zip" "Zot")))
CL-USER> (sort-table *data*)
(("" "q" "z") ("a" "b" "c") ("zap" "zip" "Zot"))
CL-USER> (sort-table *data* :column 2)
(("zap" "zip" "Zot") ("a" "b" "c") ("" "q" "z"))
CL-USER> (sort-table *data* :column 1)
(("a" "b" "c") ("" "q" "z") ("zap" "zip" "Zot"))
CL-USER> (sort-table *data* :column 1 :reverse t)
(("zap" "zip" "Zot") ("" "q" "z") ("a" "b" "c"))
CL-USER> (sort-table *data* :ordering (lambda (a b) (> (length a) (length b))))
(("zap" "zip" "Zot") ("a" "b" "c") ("" "q" "z"))


In E, as in Java and Smalltalk, optional parameters are defined as different methods with the same base name. Methods are distinguished by name (verb) and number of parameters (arity).

def defaultOrdering(a, b) { return a.op__cmp(b) }
def sort {
to run(table) {
return sort(table, 0, false, defaultOrdering)
to run(table, column) {
return sort(table, column, false, defaultOrdering)
to run(table, column, reverse) {
return sort(table, column, reverse, defaultOrdering)
to run(table :List[List[String]], column :int, reverse :boolean, ordering) {
return table.sort(fn a, b {
def ord := ordering(a[column], b[column])
if (reverse) { -ord } else { ord }

Named parameters are not builtin, but map-patterns may be used as a substitute. (TODO: Example of this)


Translation of: Ruby
defmodule Optional_parameters do
def sort( table, options\\[] ) do
options = options ++ [ ordering: :lexicographic, column: 0, reverse: false ]
ordering = options[ :ordering ]
column = options[ :column ]
reverse = options[ :reverse ]
sorted = sort( table, ordering, column )
if reverse, do: Enum.reverse( sorted ), else: sorted
defp sort( table, :lexicographic, column ) do
Enum.sort_by( table, &elem( &1, column ) )
defp sort( table, :numeric, column ) do
Enum.sort_by( table, &elem( &1, column ) |> String.to_integer )
def task do
table = [ { "123", "456", "0789" },
{ "456", "0789", "123" },
{ "0789", "123", "456" } ]
IO.write "sort defaults "; IO.inspect sort( table )
IO.write " & reverse "; IO.inspect sort( table, reverse: true )
IO.write "sort column 2 "; IO.inspect sort( table, column: 2)
IO.write " & reverse "; IO.inspect sort( table, column: 2, reverse: true)
IO.write "sort numeric "; IO.inspect sort( table, ordering: :numeric)
IO.write " & reverse "; IO.inspect sort( table, ordering: :numeric, reverse: true)
sort defaults [{"0789", "123", "456"}, {"123", "456", "0789"}, {"456", "0789", "123"}]
 & reverse    [{"456", "0789", "123"}, {"123", "456", "0789"}, {"0789", "123", "456"}]
sort column 2 [{"123", "456", "0789"}, {"456", "0789", "123"}, {"0789", "123", "456"}]
 & reverse    [{"0789", "123", "456"}, {"456", "0789", "123"}, {"123", "456", "0789"}]
sort numeric  [{"123", "456", "0789"}, {"456", "0789", "123"}, {"0789", "123", "456"}]
 & reverse    [{"0789", "123", "456"}, {"456", "0789", "123"}, {"123", "456", "0789"}]


-module( optional_parameters ).
-export( [sort/2, task/0] ).
sort( Table, Options ) ->
Ordering = proplists:get_value( ordering, Options, lexicographic ),
Column = proplists:get_value( column, Options, 1 ),
Is_reverse = proplists:get_value( reverse, Options, false ),
Sorted = sort( Table, Ordering, Column ),
sorted_reverse( Is_reverse, Sorted ).
task() ->
io:fwrite( "sort defaults ~p~n", [sort( table(), [])] ),
io:fwrite( "reverse ~p~n", [sort( table(), [reverse])] ),
io:fwrite( "sort column 3 ~p~n", [sort( table(), [{column, 3}])] ),
io:fwrite( "reverse ~p~n", [sort( table(), [{column, 3}, reverse])] ),
io:fwrite( "sort numeric ~p~n", [sort( table(), [{ordering, numeric}])] ),
io:fwrite( "reverse ~p~n", [sort( table(), [{ordering, numeric}, reverse])] ).
row_numeric( Tuple ) -> erlang:list_to_tuple( [{erlang:list_to_integer(X), X} || X <- erlang:tuple_to_list(Tuple)] ).
row_remove_numeric( Tuple ) -> erlang:list_to_tuple( [Y || {_X, Y} <- erlang:tuple_to_list(Tuple)] ).
sort( Table, lexicographic, Column ) -> lists:keysort( Column, Table );
sort( Table, numeric, Column ) ->
Numeric_table = [row_numeric(X) || X <- Table],
Sorted_numeric = lists:keysort( Column, Numeric_table ),
[row_remove_numeric(X) || X <- Sorted_numeric].
sorted_reverse( true, Sorted ) -> lists:reverse( Sorted );
sorted_reverse( false, Sorted ) -> Sorted.
table() -> [table_row1(), table_row2(), table_row3()].
table_row1() -> {"123", "456", "0789"}.
table_row2() -> {"456", "0789", "123"}.
table_row3() -> {"0789", "123", "456"}.
23> optional_parameters:task().
sort defaults [{"0789","123","456"},{"123","456","0789"},{"456","0789","123"}]
reverse [{"456","0789","123"},{"123","456","0789"},{"0789","123","456"}]
sort column 3 [{"123","456","0789"},{"456","0789","123"},{"0789","123","456"}]
reverse [{"0789","123","456"},{"456","0789","123"},{"123","456","0789"}]
sort numeric [{"123","456","0789"},{"456","0789","123"},{"0789","123","456"}]
reverse [{"0789","123","456"},{"456","0789","123"},{"123","456","0789"}]


Works with: Fortran version 95 and later

In Fortran, each argument has its "name". The optional attribute can be used to specify that an argument is optional, and its presence (or absence) can be tested using the present intrinsic (so that we can give a default value, or execute accordingly a totally different code).

module ExampleOptionalParameter
! use any module needed for the sort function(s)
! and all the interfaces needed to make the code work
implicit none
subroutine sort_table(table, ordering, column, reverse)
type(table_type), intent(inout) :: table
integer, optional :: column
logical, optional :: reverse
optional :: ordering
integer function ordering(a, b)
type(table_element), intent(in) :: a, b
end function ordering
end interface
integer :: the_column, i
logical :: reversing
type(table_row) :: rowA, rowB
if ( present(column) ) then
if ( column > get_num_of_columns(table) ) then
! raise an error?
the_column = column
end if
the_column = 1 ! a default value, de facto
end if
reversing = .false. ! default value
if ( present(reverse) ) reversing = reverse
! loops over the rows to sort... at some point, we need
! comparing an element (cell) of the row, with the element
! in another row; ... let us suppose rowA and rowB are
! the two rows we are considering
ea = get_element(rowA, the_column)
eb = get_element(rowB, the_column)
if ( present(ordering) ) then
if ( .not. reversing ) then
if ( ordering(ea, eb) > 0 ) then
! swap the rowA with the rowB
end if
else ! < instead of >
if ( ordering(ea, eb) < 0 ) then
! swap the rowA with the rowB
end if
end if
if ( .not. reversing ) then
if ( lexinternal(ea, eb) > 0 ) then
! swap the rowA with the rowB
end if
else ! < instead of >
if ( lexinternal(ea, eb) < 0 ) then
! swap the rowA with the rowB
end if
end if
end if
! ... more of the sorting algo ...
! ... and rows traversing ... (and an exit condition of course!)
end do
end subroutine sort_table
end module ExampleOptionalParameter
program UsingTest
use ExampleOptionalParameter
implicit none
type(table_type) :: table
! create the table...
! sorting taking from column 1, not reversed, using internal
! default comparator
call sort_table(table)
! the same as above, but in reversed order; we MUST specify
! the name of the argument since it is not given in the same
! order of the subroutine spec
call sort_table(table, reverse=.true.)
! sort the table using a custom comparator
call sort_table(table, my_cmp)
! or
call sort_table(table, ordering=my_cmp)
! as above, but taking from column 2
call sort_table(table, my_cmp, 2)
! or (swapping the order of args for fun)
call sort_table(table, column=2, ordering=my_cmp)
! with custom comparator, column 2 and reversing...
call sort_table(table, my_cmp, 2, .true.)
! of course we can swap the order of optional args
! by prefixing them with the name of the arg
! sort from column 2, with internal comparator
call sort_table(table, column=2)
end program UsingTest


Translation of: Oz

F# supports optional parameters for members only, not for free-standing functions.

Optional parameters are marked by using a question mark in front of the identifier. Their values are passed as option types, i.e. as Some value or None. The helper function defaultArg can be used to specify default values. In the example below, we use shadowing in order to reuse the identifiers ordering, column and reverse.

Typically, parameters are named at the caller site when optional parameters are involved. However, this is not technically required as long as only right-most arguments are omitted.

type Table(rows:string[][]) =
// in-place sorting of rows
member x.Sort(?ordering, ?column, ?reverse) =
let ordering = defaultArg ordering compare
let column = defaultArg column 0
let reverse = defaultArg reverse false
let factor = if reverse then -1 else 1
let comparer (row1:string[]) (row2:string[]) =
factor * ordering row1.[column] row2.[column]
Array.sortInPlaceWith comparer rows
member x.Print() =
for row in rows do printfn "%A" row
// Example usage
let t = new Table([| [|"a"; "b"; "c"|]
[|""; "q"; "z"|]
[|"can"; "z"; "a"|] |])
printfn "Unsorted"; t.Print()
printfn "Default sort"; t.Print()
printfn "Sorted by col. 2"; t.Print()
printfn "Sorted by col. 1"; t.Print()
t.Sort(column=1, reverse=true)
printfn "Reverse sorted by col. 1"; t.Print()
t.Sort(ordering=fun s1 s2 -> compare s2.Length s1.Length)
printfn "Sorted by decreasing length"; t.Print()


[|"a"; "b"; "c"|]
[|""; "q"; "z"|]
[|"can"; "z"; "a"|]
Default sort
[|""; "q"; "z"|]
[|"a"; "b"; "c"|]
[|"can"; "z"; "a"|]
Sorted by col. 2
[|"can"; "z"; "a"|]
[|"a"; "b"; "c"|]
[|""; "q"; "z"|]
Sorted by col. 1
[|"a"; "b"; "c"|]
[|""; "q"; "z"|]
[|"can"; "z"; "a"|]
Reverse sorted by col. 1
[|"can"; "z"; "a"|]
[|""; "q"; "z"|]
[|"a"; "b"; "c"|]
Sorted by decreasing length
[|"can"; "z"; "a"|]
[|"a"; "b"; "c"|]
[|""; "q"; "z"|]


The most idiomatic way to write this particular sorting function would be a single function that required all three parameters. Wherever practical in Go, the zero value is used as a default, and that seems meaningful in this situation. Calling t.sort(nil, 0, false) to "take the defaults" would make sense. This approach is probably closest to "positional parameters" mentioned in the task description.

In the spirit of the task though, another solution would be to pass a struct with the three "parameters" as fields. While Go does not have named function parameters, it does have named fields in struct literals. Given,

type spec struct {
ordering func(cell, cell) bool
column int
reverse bool

the following struct literal fills in zero values for ordering and column and assigns true to the field reverse.

spec{reverse: true}

Structs in Go are values and are copied when passed as parameters. The result of having a single struct parameter is that the three fields are pushed on the stack, just about like they would if they were separate parameters. The effect is named parameters with unmentioned parameters defaulting to their zero value.

A complete program to demonstrate:

package main
import (
type cell string
type row []cell
type table struct {
rows []row
column int
less func(cell, cell) bool
func (c cell) String() string {
return fmt.Sprintf("%q", string(c))
func (t table) printRows(heading string) {
fmt.Println("--", heading)
for _, row := range t.rows {
// sort.Interface
func (t table) Len() int { return len(t.rows) }
func (t table) Swap(i, j int) { t.rows[i], t.rows[j] = t.rows[j], t.rows[i] }
func (t table) Less(i, j int) bool {
return t.less(t.rows[i][t.column], t.rows[j][t.column])
// struct implements named parameter-like capability
type spec struct {
ordering func(cell, cell) bool
column int
reverse bool
func (t *table) sort(s spec) {
// set up column and comparison function for sort
t.column = s.column
switch {
case s.ordering != nil:
t.less = s.ordering
case s.reverse:
t.less = func(a, b cell) bool { return a > b }
t.less = func(a, b cell) bool { return a < b }
// sort
// reverse if necessary
if s.ordering == nil || !s.reverse {
last := len(t.rows) - 1
for i := last / 2; i >= 0; i-- {
t.rows[i], t.rows[last-i] = t.rows[last-i], t.rows[i]
func main() {
t := table{rows: []row{
{"pail", "food"},
{"pillbox", "nurse maids"},
{"suitcase", "airedales"},
{"bathtub", "chocolate"},
{"schooner", "ice cream sodas"},
// no "parameters"
t.printRows("sorted on first column")
// "named parameter" reverse.
t.sort(spec{reverse: true})
t.printRows("reverse sorted on first column")
// "named parameters" column and ordering
column: 1,
ordering: func(a, b cell) bool { return len(a) > len(b) },
t.printRows("sorted by descending string length on second column")


-- song
["pail" "food"]
["pillbox" "nurse maids"]
["suitcase" "airedales"]
["bathtub" "chocolate"]
["schooner" "ice cream sodas"]

-- sorted on first column
["bathtub" "chocolate"]
["pail" "food"]
["pillbox" "nurse maids"]
["schooner" "ice cream sodas"]
["suitcase" "airedales"]

-- reverse sorted on first column
["suitcase" "airedales"]
["schooner" "ice cream sodas"]
["pillbox" "nurse maids"]
["pail" "food"]
["bathtub" "chocolate"]

-- sorted by descending string length on second column
["schooner" "ice cream sodas"]
["pillbox" "nurse maids"]
["suitcase" "airedales"]
["bathtub" "chocolate"]
["pail" "food"]


Optional Parameters:

def orderedSort(Collection table, column = 0, reverse = false, ordering = {x, y -> x <=> y } as Comparator) {
table.sort(false) { x, y -> (reverse ? -1 : 1) *[column], y[column])}

Test code:

def table = [['a', 'b', 'c'], ['', 'q', 'z'], ['zap', 'zip', 'Zot']]
assert orderedSort(table) == [['', 'q', 'z'], ['a', 'b', 'c'], ['zap', 'zip', 'Zot']]
assert orderedSort(table, 2) == [['zap', 'zip', 'Zot'], ['a', 'b', 'c'], ['', 'q', 'z']]
assert orderedSort(table, 1) == [['a', 'b', 'c'], ['', 'q', 'z'], ['zap', 'zip', 'Zot']]
assert orderedSort(table, 1, true) == [['zap', 'zip', 'Zot'],['', 'q', 'z'],['a', 'b', 'c']]
assert orderedSort(table, 0, false, {x, y -> y?.size() <=> x?.size()} as Comparator) == [['zap', 'zip', 'Zot'],['a', 'b', 'c'],['', 'q', 'z']]

Named Parameters:

Collection.metaClass.orderedSort = { params ->
def column = params?.column ?: 0
def reverse = params?.reverse ?: false
def ordering = params?.ordering ?: {x, y -> x <=> y } as Comparator
table.sort(false) { x, y -> (reverse ? -1 : 1) *[column], y[column])}

Test Code:

def table = [['a', 'b', 'c'], ['', 'q', 'z'], ['zap', 'zip', 'Zot']]
assert table.orderedSort() == [['', 'q', 'z'], ['a', 'b', 'c'], ['zap', 'zip', 'Zot']]
assert table.orderedSort(column: 2) == [['zap', 'zip', 'Zot'], ['a', 'b', 'c'], ['', 'q', 'z']]
assert table.orderedSort(column: 1) == [['a', 'b', 'c'], ['', 'q', 'z'], ['zap', 'zip', 'Zot']]
assert table.orderedSort(column: 1, reverse: true) == [['zap', 'zip', 'Zot'],['', 'q', 'z'],['a', 'b', 'c']]
assert table.orderedSort(ordering: {x, y -> y?.size() <=> x?.size()} as Comparator) == [['zap', 'zip', 'Zot'],['a', 'b', 'c'],['', 'q', 'z']]


Option 1: Using haskell's record update syntax, we can simulate named default arguments. This method has the drawback of not allowing for a parameter to be positional and named simultaneously.

{-# LANGUAGE RecordWildCards #-}
data SorterArgs = SorterArgs { cmp :: String, col :: Int, rev :: Bool } deriving Show
defSortArgs = SorterArgs "lex" 0 False
sorter :: SorterArgs -> [[String]] -> [[String]]
sorter (SorterArgs{..}) = case cmp of
_ -> undefined
main = do
sorter defSortArgs{cmp = "foo", col=1, rev=True} [[]]
sorter defSortArgs{cmp = "foo"} [[]]
sorter defSortArgs [[]]
return ()

Option 2: This method has the drawback of being a bit verbose and requiring you to supply "Maybe a" arguments.

import Data.Maybe (fromMaybe)
-- Use fromMaybe as an operator because its prettier
(//) = flip fromMaybe
sorter :: Maybe String -> Maybe Int -> Maybe Bool -> [[String]] -> [[String]]
sorter ((// "lex") -> cmp)
((// 0) -> col)
((// False) -> rev) = undefined
main = do
sorter (Just "foo") (Just 1) (Just True)
sorter Nothing Nothing Nothing

Icon and Unicon[edit]

Optional named parameters are not the norm in Icon/Unicon. In the example below bubblesortf would be a version of Bubble Sort modified to sort on a column number (Ordering is already supported). It could equally be replaced by any similarly modified Rosetta sort. The use of reverse on a list is a Unicon extension; in Icon a procedure from the IPL must be linked.

procedure main()
X := [ [1,2,3], [2,3,1], [3,1,2]) # A list of lists
Sort(X) # vanilla sort
Sort(X,"ordering","numeric","column",2,"reverse") # using optional parameters
procedure Sort(X,A[]) # A[] provides for a variable number of arguments
while a := get(A) do {
case a of {
"ordering" : op := case get(A) | runerr(205,a) of {
"lexicographic"|"string": "<<"
"numeric": "<"
default: runerr(205,op)
"column" : col := 0 < integer(col := get(A)) | runerr(205,col)
"reverse" : reverseorder := reverse
default: runerr(205,a)
return (\reverseorder|1)(bubblesortf(X,\c|1,\op|"<<")) # reverse or return the sorted list


srtbl=: verb define
'' srtbl y
'`ordering column reverse'=. x , (#x)}. ]`0:`0:
|.^:reverse y /: ordering (column {"1 ])y

For simplicity, the optional arguments are all functions, and are positional (on the left -- the table, with its arbitrary number of rows and columns, is on the right). Note also that the ordering function is expected to map its entire argument (since this offers much better efficiencies than a binary comparison).

Example Use

   ]Table=: ('a';'b';'c'),('';'q';'z'),:'zip';'zap';'Zot'
│a │b │c │
│ │q │z │
srtbl Table NB. default sort
│ │q │z │
│a │b │c │
]`1: srtbl Table NB. sort by column 1
│a │b │c │
│ │q │z │
]`2:`1: srtbl Table NB. reverse sort by column 2
│ │q │z │
│a │b │c │
#&>`0: srtbl Table NB. sort by length
│ │q │z │
│a │b │c │


Java has no optional parameters, but methods can be overloaded on the number and types of arguments, which can be used to effectively achieve optional positional parameters.

import java.util.*;
public class OptionalParams {
// "natural ordering" comparator
static <T extends Comparable<? super T>> Comparator<T> naturalOrdering() {
return Collections.reverseOrder(Collections.<T>reverseOrder());
public static <T extends Comparable<? super T>> void
sortTable(T[][] table) {
sortTable(table, 0);
public static <T extends Comparable<? super T>> void
sortTable(T[][] table,
int column) {
sortTable(table, column, false);
public static <T extends Comparable<? super T>> void
sortTable(T[][] table,
int column, boolean reverse) {
sortTable(table, column, reverse, OptionalParams.<T>naturalOrdering());
public static <T> void sortTable(T[][] table,
final int column,
final boolean reverse,
final Comparator<T> ordering) {
Comparator<T[]> myCmp = new Comparator<T[]>() {
public int compare(T[] x, T[] y) {
return (reverse ? -1 : 1) *[column], y[column]);
Arrays.sort(table, myCmp);
public static void main(String[] args) {
String[][] data0 = {{"a", "b", "c"},
{"", "q", "z"},
{"zap", "zip", "Zot"}};
// prints: [[a, b, c], [, q, z], [zap, zip, Zot]]
// we copy it so that we don't change the original copy
String[][] data = data0.clone();
// prints: [[, q, z], [a, b, c], [zap, zip, Zot]]
data = data0.clone();
sortTable(data, 2);
// prints: [[zap, zip, Zot], [a, b, c], [, q, z]]
data = data0.clone();
sortTable(data, 1);
// prints: [[a, b, c], [, q, z], [zap, zip, Zot]]
data = data0.clone();
sortTable(data, 1, true);
// prints: [[zap, zip, Zot], [, q, z], [a, b, c]]
data = data0.clone();
sortTable(data, 0, false, new Comparator<String>() {
public int compare(String a, String b) {
return b.length() - a.length();
// prints: [[zap, zip, Zot], [a, b, c], [, q, z]]


See Named parameters#JavaScript, to pass named parameters one uses an object with properties set:

function sorter(table, options) {
opts = {}
opts.ordering = options.ordering || 'lexicographic';
opts.column = options.column || 0;
opts.reverse = options.reverse || false;
// ...
sorter(the_data, {reverse: true, ordering: 'numeric'});


In jq, there are two approaches to defining optional parameters:

  • Using a JSON object to define the parameters;
  • Using jq's support for multiple arities (in versions of jq higher than 1.4)

The first approach gives the most flexibility, but it is sometimes tedious to use unless augmented by the second approach.

The second approach can be used if jq > 1.4 is available and if it acceptable to define a hierarchy of parameters, so that the first parameter becomes required if the second is given, and so on. The strictures of this approach can often be alleviated by using dynamic typing.

In this section, we will focus on the first approach as that is supported by all versions of jq, and because it illustrates an important point - that in jq, the value of a field (or tag) within an object can be specified as a 0-arity filter, even though functions are not JSON objects.

An aside on jq and JSON objects

Since jq objects are JSON objects, it might be surprising that arity-0 filters can be specified as a value within a JSON object. This is possible because of the way expressions such as {"function": f} are interpreted by jq. The key to understanding this is that jq functions are compiled into closures. Here is an example:

def bar: 2 *.;
def foo: {"a": bar};

The expression 3 | foo.a evaluates to 6.

Preliminaries: In accordance with the task description, we will also suppose that sort_table(ordering; column; reverse) is already defined. To specify the lexicographic ordering on strings in terms of an arity-0 filter, we define less_than_or_equal/0 as follows:

def less_than_or_equal: .[0] <= .[1];

The Task:

def sorter(options):
sort_table( if (options|has("ordering")) then options.ordering
else less_than_or_equal
options.column or 0;
options.reverse or false );
# If jq > 1.4 is being used, we may also define:
def sorter: sorter({});


[1,2] | sorter({ "reverse": true, "ordering": less_than_or_equal } )
[1,2] | sorter({ "reverse": true })
# If sorter/0 has also been defined:
[1,2] | sorter


Julia supports both named and positional optional parameters. We can define both versions at the same time if we want:

sorttable(T; ordering=<, column=1, reverse=false) =
sort(T, by = t -> t[column], lt = reverse ? (a,b) -> ordering(b,a) : ordering)
sorttable(T, ordering=<, column=1, reverse=false) =
sorttable(T, ordering=ordering, column=column, reverse=reverse)

where the ; in the argument list denotes the named-parameter variant, and we have used Julia's built-in higher-order sort function to do the work. Note that we simply pass a comparison function for the ordering, and the built-in < operator is actually just a function that (on strings) compares in lexicographic order.

Example output:

julia> data = {["a", "b", "c"], ["", "q", "z"], ["zap", "zip", "Zot"]}
3-element Array{Any,1}:
julia> sorttable(data, column=2, reverse=true) # named arguments
3-element Array{Any,1}:
julia> sorttable(data, >, 2) # the same thing, with positional arguments
3-element Array{Any,1}:


Lasso can handle both positional and named params. Methods support multiple dispatch where each dispatch defines it's own set of parameters.

define sortarray( // params are set by position
items::array, // required param
ordering::string = 'lexicographic', // optional param
column::integer = 1,
reverse::boolean = false
) => {
// sorting process
local(sorteditems = array)
// Lasso has no build in method to sort an array of arrays by position in the contained arrays
// But a method could be built for it
return #sorteditems
define sortarray(
-items::array, // required param
-ordering::string = 'lexicographic', // optional param
-column::integer = 1,
-reverse::boolean = false
) => sortarray(#items, #ordering, #column, #reverse)
local(items = array(
array(10, 'red', 'Volvo'),
array(15, 'gren', 'Ford'),
array(48, 'yellow', 'Kia'),
array(12, 'black', 'Holden'),
array(19, 'brown', 'Fiat'),
array(8, 'pink', 'Batmobile'),
array(74, 'orange', 'Bicycle')
sortarray(-items = #items, -reverse)


TIScript allows to define optional parameters with default values:

function sorter(table, ordering = "lexicographic", column = 0, reverse = false) {
// ...


Works with: UCB Logo
to sort :table [:column 1] [:ordering "before?] [:reverse "false]
 ; ...

The function "sort" has a default arity of 1 for the required parameter. When overriding default parameters, you must wrap the call in parentheses to specify the different arity.

sort :table
(sort :table 2)
(sort :table 3 "less? "true)


function showTable(tbl)
if type(tbl)=='table' then
local result = {}
for _, val in pairs(tbl) do
table.insert(result, showTable(val))
return '{' .. table.concat(result, ', ') .. '}'
return (tostring(tbl))
function sortTable(op)
local tbl = op.table or {}
local column = op.column or 1
local reverse = op.reverse or false
local cmp = op.cmp or (function (a, b) return a < b end)
local compareTables = function (a, b)
local result = cmp(a[column], b[column])
if reverse then return not result else return result end
table.sort(tbl, compareTables)
A = {{"quail", "deer", "snake"},
{"dalmation", "bear", "fox"},
{"ant", "cougar", "coyote"}}
print('original', showTable(A))
print('defaults', showTable(A))
sortTable{table=A, column=2}
print('col 2 ', showTable(A))
sortTable{table=A, column=3}
print('col 3 ', showTable(A))
sortTable{table=A, column=3, reverse=true}
print('col 3 rev', showTable(A))
sortTable{table=A, cmp=(function (a, b) return #a < #b end)}
print('by length', showTable(A))
original        {{quail, deer, snake}, {dalmation, bear, fox}, {ant, cougar, coyote}}
defaults        {{ant, cougar, coyote}, {dalmation, bear, fox}, {quail, deer, snake}}
col 2           {{dalmation, bear, fox}, {ant, cougar, coyote}, {quail, deer, snake}}
col 3           {{ant, cougar, coyote}, {dalmation, bear, fox}, {quail, deer, snake}}
col 3 rev       {{quail, deer, snake}, {dalmation, bear, fox}, {ant, cougar, coyote}}
by length       {{ant, cougar, coyote}, {quail, deer, snake}, {dalmation, bear, fox}}


OptionalSort := proc(input, {
ordering :: Or(procedures,identical("lexicographic")) := "lexicographic",
column :: posint := 1,
reverse :: truefalse := false
} )
local compare;
if ordering = "lexicographic" then
compare := (x,y)->evalb(`if`(reverse,x[column]>=y[column],x[column]<=y[column]));
compare := (x,y)->`if`(reverse,ordering(x[column],y),ordering(y,x));
end if;
sort( input, compare );
end proc:

Some examples of this procedure in action:

> L := [[1, 2], [3, 4], [-5, 7]]:
> OptionalSort(L);
[[-5, 7], [1, 2], [3, 4]]
> OptionalSort(L, reverse);
[[3, 4], [1, 2], [-5, 7]]
> OptionalSort(L, reverse, column = 2);
[[-5, 7], [3, 4], [1, 2]]


Options[OptionalSort]={ordering->lexicographic,column->1,reverse-> False};
SortBy[x ,#[[OptionValue[column]]]&]//Reverse,
SortBy[x,#[[OptionValue[column]]]&] ]
OptionalSort[{{"a" ,"b", "c"}, {"", "q", "z"},{"zap" ,"zip", "Zot"}} ]
OptionalSort[{{"a" ,"b", "c"}, {"", "q", "z"},{"zap" ,"zip", "Zot"}},{ordering->lexicographic,column->2,reverse-> True} ]


It's possible to use either optional parameters or overloading on parameter number (or type). However, it's less code repetition to use optional parameters when possible (unless, of course, the implementation varies drastically with different parameters).

Sorter (table : list[list[string]], ordering = "lexicographic", column = 0, reverse = false) : list[list[string]]
// implementation goes here


import algorithm, strutils, future
proc printTable(a) =
for row in a:
for x in row: stdout.write x, repeatChar(4 - x.len)
echo ""
echo ""
proc sortTable(a: seq[seq[string]], column = 0, reverse = false,
ordering: (proc(a,b: string): int) = system.cmp) : seq[seq[string]] =
let order = if reverse: Descending else: Ascending
result = a
result.sort(proc(x,y:seq[string]):int = ordering(x[column],y[column]), order)
const data = @[@["a", "b", "c"], @["", "q", "z"], @["zap", "zip", "Zot"]]
printTable data
printTable sortTable(data)
printTable sortTable(data, column = 2)
printTable sortTable(data, column = 1)
printTable sortTable(data, column = 1, reverse = true)
printTable sortTable(data, ordering = (a,b) => cmp[int](b.len,a.len))


a   b   c   
    q   z   
zap zip Zot 

    q   z   
a   b   c   
zap zip Zot 

zap zip Zot 
a   b   c   
    q   z   

a   b   c   
    q   z   
zap zip Zot 

zap zip Zot 
    q   z   
a   b   c   

zap zip Zot 
a   b   c   
    q   z 


Without getting into any detail, here is one way you might implement optional arguments. (Note that since Objective-C is a strict superset of C, any C solution can be used as well.)

typedef enum { kOrdNone, kOrdLex, kOrdByAddress, kOrdNumeric } SortOrder;
@interface MyArray : NSObject {}
// . . .
@implementation MyArray
- (void)sort {
[self sortWithOrdering:kOrdLex onColumn:0 reversed:NO];
- (void)sortWithOrdering:(SortOrder)ord {
[self sortWithOrdering:ord onColumn:0 reversed:NO];
- (void)sortWithOrdering:(SortOrder)ord onColumn:(int)col {
[self sortWithOrdering:ord onColumn:col reversed:NO];
- (void)sortWithOrdering:(SortOrder)ord onColumn:(int)col reversed:(BOOL)rev {
// . . . Actual sort goes here . . .


OCaml has optional named parameters. It is conventional to place a non-optional parameter after the optional parameters, because if the optional parameters were at the end, then if you don't provide them, it will just look like a partial application (because OCaml supports currying), resulting in a function which still expects the optional parameters.

let sort_table ?(ordering = compare) ?(column = 0) ?(reverse = false) table =
let cmp x y = ordering (List.nth x column) (List.nth y column) * (if reverse then -1 else 1) in
List.sort cmp table

Example uses:

# let data = [["a"; "b"; "c"]; [""; "q"; "z"]; ["zap"; "zip"; "Zot"]];;
val data : string list list =
[["a"; "b"; "c"]; [""; "q"; "z"]; ["zap"; "zip"; "Zot"]]
# sort_table data;;
- : string list list =
[[""; "q"; "z"]; ["a"; "b"; "c"]; ["zap"; "zip"; "Zot"]]
# sort_table ~column:2 data;;
- : string list list =
[["zap"; "zip"; "Zot"]; ["a"; "b"; "c"]; [""; "q"; "z"]]
# sort_table ~column:1 data;;
- : string list list =
[["a"; "b"; "c"]; [""; "q"; "z"]; ["zap"; "zip"; "Zot"]]
# sort_table ~column:1 ~reverse:true data;;
- : string list list =
[["zap"; "zip"; "Zot"]; [""; "q"; "z"]; ["a"; "b"; "c"]]
# sort_table ~ordering:(fun a b -> compare (String.length b) (String.length a)) data;;
- : string list list =
[["zap"; "zip"; "Zot"]; ["a"; "b"; "c"]; [""; "q"; "z"]]

OCaml does not support optional positional parameters, because, since OCaml supports currying, it would conflict with partial applications, where you do not provide all the arguments to a function, and it results in a function which expects the remaining arguments.


Oz supports optional parameters only for methods, not for functions.

class Table
meth init(Rows)
rows := Rows
meth sort(ordering:O<=Lexicographic column:C<=1 reverse:R<=false)
fun {Predicate Row1 Row2}
Res = {O {Nth Row1 C} {Nth Row2 C}}
if R then {Not Res} else Res end
rows := {Sort @rows Predicate}
fun {Lexicographic As Bs} %% omitted for brevity
T = {New Table init([["a" "b" "c"] ["" "q" "z"] ["zap" "zip" "Zot"]])}
{T sort}
{T sort(column:3)}
{T sort(column:2)}
{T sort(column:2 reverse:true)}
{T sort(ordering:fun {$ A B} {Length B} < {Length A} end)}


As it happens the built-in vecsort() function fulfills all the requirements of this task. In general optional arguments are handled in GP by default values:

sort(v, ordering=0, column=0, reverse=0)

while in PARI it is handled by checking for NULL (assuming parser code DG, see 5.7.3 in the User's Guide to the PARI library):

GP;install("test_func", "vDG", "test", "path/to/");

test_func(GEN x) {
if (x == NULL)
pari_printf("Argument omitted.\n");
pari_printf("Argument was: %Ps\n", x);


Perl 5 has no formal parameters, so all function arguments must be processed in the function body.

This function expects its first argument to be a reference to an array of arrays. It interprets any remaining arguments as a hash of optional parameters.

sub sorttable
{my @table = @{shift()};
my %opt =
(ordering => sub {$_[0] cmp $_[1]}, column => 0, reverse => 0, @_);
my $col = $opt{column};
my $func = $opt{ordering};
my @result = sort
{$func->($a->[$col], $b->[$col])}
return ($opt{reverse} ? [reverse @result] : \@result);}

An example of use:

my $a = [["a", "b", "c"], ["", "q", "z"], ["zap", "zip", "Zot"]];
foreach (@{sorttable $a, column => 1, reverse => 1})
{foreach (@$_)
{printf "%-5s", $_;}
print "\n";}

Perl 6[edit]

Using named parameters:

method sorttable(:$column = 0, :$reverse, :&ordering = &infix:<cmp>) {
my @result = self»[$column].sort: &ordering;
return $reverse ?? @result.reverse !! @result;


Optional parameters are specified simply by declaring a default value. They must however be grouped on the right.

function increment(integer i, integer inc=1)
return i+inc
end function
?increment(5) -- shows 6
?increment(5,2) -- shows 7

You can also use a variable length sequence to emulate optional parameters.

printf(1,"%d records sorted in %3.2s\n",{records,time()-t0})

In other words printf always accepts exactly three arguments, but the third should contain the correct number of elements to match the number of format specifications in the second argument.

The following incomplete snippet from demo\pGUI\listview.exw shows the basic idea for sorting a table by any column, up or down:

integer sortcol = 0
integer sortdir = 1
function by_column(integer i, integer j)
return sortdir*compare(data[i][sortcol],data[j][sortcol])
end function
sequence tags = tagset(table_size) -- {1,2,..table_size}
function click_cb(Ihandle self, integer l, integer c, atom pStatus)
string sortc
sortc = sprintf("SORTSIGN%d",c)
sortdir = iff(IupGetAttribute(self,sortc)="DOWN"?-1:1)
sortcol = c
tags = custom_sort(routine_id("by_column"),tags)
function value_cb(Ihandle /*self*/, integer l, integer c)
l = tags[l]
return data[l][c]
end function


(de sortTable (Tbl . @)
(let (Ordering prog Column 1 Reverse NIL) # Set defaults
(bind (rest) # Bind optional params
(setq Tbl
(by '((L) (Ordering (get L Column)))
Tbl ) )
(if Reverse (flip Tbl) Tbl) ) ) )


(de *Data ("a" "bcdef" "X") (" " "qrst" "z") ("zap" "zip" "Zot"))

: (sortTable *Data)
-> ((" " "qrst" "z") ("a" "bcdef" "X") ("zap" "zip" "Zot"))

: (sortTable *Data '(Reverse . T))
-> (("zap" "zip" "Zot") ("a" "bcdef" "X") (" " "qrst" "z"))

: (sortTable *Data '(Column . 2) '(Ordering . length))
-> (("zap" "zip" "Zot") (" " "qrst" "z") ("a" "bcdef" "X"))

: (sortTable *Data '(Ordering . uppc) '(Column . 3))
-> (("a" "bcdef" "X") (" " "qrst" "z") ("zap" "zip" "Zot"))


Works with: Python version 2.x
only (the "cmp" argument to sorted() is no longer accepted in Python 3)

Using a pretty-printer for the table

>>> def printtable(data):
for row in data:
print ' '.join('%-5s' % ('"%s"' % cell) for cell in row)
>>> import operator
>>> def sorttable(table, ordering=None, column=0, reverse=False):
return sorted(table, cmp=ordering, key=operator.itemgetter(column), reverse=reverse)
>>> data = [["a", "b", "c"], ["", "q", "z"], ["zap", "zip", "Zot"]]
>>> printtable(data)
"a" "b" "c"
"" "q" "z"
"zap" "zip" "Zot"
>>> printtable( sorttable(data) )
"" "q" "z"
"a" "b" "c"
"zap" "zip" "Zot"
>>> printtable( sorttable(data, column=2) )
"zap" "zip" "Zot"
"a" "b" "c"
"" "q" "z"
>>> printtable( sorttable(data, column=1) )
"a" "b" "c"
"" "q" "z"
"zap" "zip" "Zot"
>>> printtable( sorttable(data, column=1, reverse=True) )
"zap" "zip" "Zot"
"" "q" "z"
"a" "b" "c"
>>> printtable( sorttable(data, ordering=lambda a,b: cmp(len(b),len(a))) )
"zap" "zip" "Zot"
"a" "b" "c"
"" "q" "z"

See the Python entry in Named Arguments for a more comprehensive description of Python function parameters and call arguments.

Note that expression for a default argument of an optional parameter is evaluated only once, when the function definition is executed, and all calls of the function where that parameter is missing will be initialized to point to that same shared object. So, if the default argument value is a mutable object (e.g. list, dict, etc.), then any changes to it will affect what is seen by future calls of the function:

>>> def foo(x, lst=[]):
...   lst.append(x)
...   print lst
>>> foo(1)
>>> foo(2)
[1, 2]
>>> foo(3)
[1, 2, 3]


Optional parameters are given using a name=value syntax within the function header.

tablesort <- function(x, ordering="lexicographic", column=1, reverse=false)
# Implementation
# Usage is e.g.
tablesort(mytable, column=3)


#lang racket
(define (sort-table table
[ordering string<=?]
[column 0]
[reverse? #f])
(sort table (if reverse?
(negate ordering)
#:key (λ (row) (list-ref row column))))


The REXX language allows for default values for positional arguments as well as an easy method to check if a string is part of a parameter.
Also allowed are named parameters.

The REXX language doesn't have any native sorting functions, so you have to write your own sorting subroutine.

sortStrings:  procedure expose @.      /*stemmed array is named:   @.   */
col=1; reverse='NO'; order='LEXICOGRAPHIC' /*set some defaults.*/
arg options
do j=1 for words(options); x=word(options,j)
when datatype(x, 'W') then col=x/1
when pos('=', x)==0 then order=x
otherwise parse var x nam '=' value
end /*select*/
end /*j*/
║ check for errors here: COL isn't a positive integer ···, ║
║ REVERSE value isn't NO or YES, ║
║ ORDER value is recognized ··· ║

... main body of string sort here ...
return /*stick a fork in it, we're done.*/

An example use is:

/*REXX example uses the   SortStrings   subroutine  with optional args. */
/*···define array (@.nnn) of strings here···*/
call sortStrings 'Reverse=no' 3
/*stick a fork in it, we're done.*/


Ruby allows default values for positional arguments, but they have disadvantages. In the next example, if you want to pass reverse=true, you must also give values for ordering and column.

def table_sort(table, ordering=:<=>, column=0, reverse=false)
# ...

Ruby 2.0 added keyword arguments to the language. These provide the most natural solution.

Works with: Ruby version 2.0
def table_sort(table, ordering: :<=>, column: 0, reverse: false)
p = ordering.to_proc
if reverse
table.sort {|a, b| p.(b[column], a[column])}
table.sort {|a, b| p.(a[column], b[column])}
# Quick example:
table = [
["Ottowa", "Canada"],
["Washington", "USA"],
["Mexico City", "Mexico"],
p table_sort(table, column: 1)

Older versions of Ruby can fake the effect with a Hash (as detailed in Named parameters#Ruby). The next example needs Ruby 1.8.7 only because the sort code calls Symbol#to_proc; the passing of parameters would yet work with Ruby older than 1.8.7.

Works with: Ruby version 1.8.7
def table_sort(table, opts = {})
defaults = {:ordering => :<=>, :column => 0, :reverse => false}
opts = defaults.merge(opts)
c = opts[:column]
p = opts[:ordering].to_proc
if opts[:reverse]
table.sort {|a, b|[c], a[c])}
table.sort {|a, b|[c], b[c])}


With Scala 2.8 optional and named parameters are build in.

  def sortTable(data: List[List[String]],
ordering: (String, String) => Boolean = (_ < _),
column: Int = 0,
reverse: Boolean = false) = {
val result = data.sortWith((a, b) => ordering(a(column), b(column)))
if (reverse) result.reverse else result
val data=List(List("a","b","c"), List("","q","z"), List("zap","zip","Zot"))
//-> List(List(a, b, c), List(, q, z), List(zap, zip, Zot))
//-> List(List(, q, z), List(a, b, c), List(zap, zip, Zot))
println(sortTable(data, reverse=true))
//-> List(List(zap, zip, Zot), List(a, b, c), List(, q, z))
println(sortTable(data, column=2))
//-> List(List(zap, zip, Zot), List(a, b, c), List(, q, z))
println(sortTable(data, ((a, b)=> b.size<a.size)))
//-> List(List(zap, zip, Zot), List(a, b, c), List(, q, z))


func table_sort(table, ordering: '<=>', column: 0, reverse: false) {
if (reverse) {
table.sort {|a,b| b[column].$ordering(a[column])}
} else {
table.sort {|a,b| a[column].$ordering(b[column])}
# Quick example:
var table = [
["Ottowa", "Canada"],
["Washington", "USA"],
["Mexico City", "Mexico"],
say table_sort(table, column: 1);
[["Ottowa", "Canada"], ["Mexico City", "Mexico"], ["Washington", "USA"]]

Missing the point, we can also create and provide a custom method for sorting to ordering:

class String {
method my_sort(arg) {
(self.len <=> arg.len) ->
|| ( <=> ->
|| (self <=> arg)
say table_sort(table, column: 1, ordering: 'my_sort');
[["Washington", "USA"], ["Ottowa", "Canada"], ["Mexico City", "Mexico"]]


In Slate, named optional parameters may be specified in the method signature, but not defaults, so there is a macro defaultsTo: for specifying that within the method body at run-time.

s@(Sequence traits) tableSort &column: column &sortBy: sortBlock &reverse: reverse
column `defaultsTo: 0.
sortBlock `defaultsTo: [| :a :b | (a lexicographicallyCompare: b) isNegative].
(reverse `defaultsTo: False)
ifTrue: [sortBlock := [| :a :b | (sortBlock applyTo: {a. b}) not]].
s sortBy: [| :a :b | sortBlock applyTo: {a at: column. b at: column}]


enum SortOrder { case kOrdNone, kOrdLex, kOrdByAddress, kOrdNumeric }
func sortTable(table: [[String]], less: (String,String)->Bool = (<), column: Int = 0, reversed: Bool = false) {
// . . . Actual sort goes here . . .


Tcl supports optional parameters to procedures through two mechanisms. It can either work positionally (through giving default values for arguments) or by using a special last argument called “args” which will collect all the remaining arguments into a list that can be processed by the procedure.

The optional positional parameter style works like this:

Works with: Tcl version 8.4
proc tablesort {table {ordering ""} {column 0} {reverse 0}} {
set direction [expr {$reverse ? "-decreasing" : "-increasing"}]
if {$ordering ne ""} {
lsort -command $ordering $direction -index $column $table
} else {
lsort $direction -index $column $table
puts [tablesort $data]
puts [tablesort $data "" 1]
puts [tablesort $data "" 0 1]
puts [tablesort $data {
apply {{a b} {expr {[string length $a]-[string length $b]}}}

When using the second style, it is often common to use Named Arguments (and in fact the “lsort” already works very much like this). Note that it is most common to use named arguments that start with a “-”, but we omit them here so that we formally match the requirements of the task.

Works with: Tcl version 8.5
package require Tcl 8.5;  # Only for the list expansion syntax
proc tablesort {table args} {
array set opt {ordering "" column 0 reverse 0}
array set opt $args
set pars [list -index $opt(column)]
if {$opt(reverse)} {lappend pars -decreasing}
if {$opt(ordering) ne ""} {lappend pars -command $opt(ordering)}
lsort {*}$pars $table
puts [tablesort $data]
puts [tablesort $data column 1]
puts [tablesort $data column 0]
puts [tablesort $data column 0 reverse 1]
puts [tablesort $data ordering {
apply {{a b} {expr {[string length $b]-[string length $a]}}}


Because functions in Ursala take only a single argument and the usual programming style is point free, the most natural way of affecting named optional function parameters is to parameterize the function by a record with computed fields. Fields in a record instance can be associated with descriptive identifiers, listed in any order, and omitted if their default values are intended.

For this task, a record type ss (for sort specification) is defined with three fields, ordering, column, and reversed. The ordering field contains a binary relational predicate, with the lexicographic relation (lleq) being the default. The column field is a natural number with a default value of 1, and the reversed field is a boolean with a default value of false. The sorter is actually a second order function taking a record of this type as an argument, and returning a function built to order that is applicable to a list of data to be sorted.

#import std
#import nat
ss ::
ordering  %fZ ~ordering||lleq!
column  %n ~column||1!
reversed  %b
sorter = +^(~reversed?/~&x! ~&!,-<+ +^/~ordering ~~+ ~&h++ //skip+ predecessor+ ~column)

Here is a test program using the function above to sort a table five different ways, mentioning only the information that differs from the defaults. The table is stored as a list of lists, with one list for each row, hence three rows and two columns.

example_table = 
<'foo','b '>,
<'barr','a '>,
#cast %sLLL
examples =
(sorter ss&) example_table, # default sorting algorithm
(sorter ss[ordering: leql]) example_table, # sort by field lengths but otherwise default
(sorter ss[column: 2]) example_table, # etc.
(sorter ss[reversed: true]) example_table,
(sorter ss[reversed: true,column: 2]) example_table>

In practice, these five functions would have been more conveniently expressed using the built in sort operator as -<&h, leql-<&h, -<&th, -<x&h, and -<x&th respectively, but this technique is useful in more complicated applications. Here is the output showing five different sorts of the table.

   <<'barr','a '>,<'bazzz','c'>,<'foo','b  '>>,
   <<'foo','b  '>,<'barr','a '>,<'bazzz','c'>>,
   <<'barr','a '>,<'foo','b  '>,<'bazzz','c'>>,
   <<'foo','b  '>,<'bazzz','c'>,<'barr','a '>>,
   <<'bazzz','c'>,<'foo','b  '>,<'barr','a '>>>


You can give any template parameter a default value using the optional "select" attribute.

<xsl:template name="sort">
<xsl:param name="table" />
<xsl:param name="ordering" select="'lexicographic'" />
<xsl:param name="column" select="1" />
<xsl:param name="reversed" select="false()" />


zkl does left to right parameters, each with an optional default. No named parameters (ala Smalltalk). There isn't type enforcement either, a parameter can be anything (although you can set a hint to tell the compiler what you think it will be). If you do want to play named parameters, you can pass in a dictionary (ala Python). The parameters are basically a [varargs] list that you can access in traditional ways.

const lex="L";
fcn mystrySort(table,ordering=lex,column=0,reverse=False,other){