Optional parameters: Difference between revisions

);</lang>

=={{header|Clojure}}==

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.

<lang Clojure>(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</lang>

=={{header|Common Lisp}}==

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

<lang lisp>(defun sort-table (table &key (ordering #'string<)

(column 0)

reverse)

(sort table (if reverse

(complement ordering)

ordering)

:key (lambda (row) (elt row column))))</lang>

(Notes: The builtin [http://www.lispworks.com/documentation/HyperSpec/Body/f_sort_.htm sort] takes a "less than" predicate function. The [http://www.lispworks.com/documentation/HyperSpec/Body/f_comple.htm complement] function inverts a predicate.)

Example uses:

<lang lisp>CL-USER> (defparameter *data* '(("a" "b" "c") ("" "q" "z") ("zap" "zip" "Zot")))

*DATA*

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"))</lang>

=={{header|F_Sharp|F#}}==

{{trans|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 <code>Some value</code> or <code>None</code>. The helper function <code>defaultArg</code> can be used to specify default values. In the example below, we use shadowing in order to reuse the identifiers <code>ordering</code>, <code>column</code> and <code>reverse</code>.

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.

<lang fsharp>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()

t.Sort()

printfn "Default sort"; t.Print()

t.Sort(column=2)

printfn "Sorted by col. 2"; t.Print()

t.Sort(column=1)

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()</lang>

Output:

<pre>Unsorted

[|"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"|]</pre>

=={{header|Raku}}==

(formerly Perl 6)

Using named parameters:

<lang perl6>method sorttable(:$column = 0, :$reverse, :&ordering = &infix:<cmp>) {

my @result = self»[$column].sort: &ordering;

return $reverse ?? @result.reverse !! @result;

}</lang>

Using optional positional parameters:

<lang perl6>method sorttable-pos($column = 0, $reverse?, &ordering = &infix:<cmp>) {

my @result = self»[$column].sort: &ordering;

return $reverse ?? @result.reverse !! @result;

}</lang>

=={{header|TIScript}}==

TIScript allows to define optional parameters with default values:

<lang javascript>function sorter(table, ordering = "lexicographic", column = 0, reverse = false) {

// ...

}

sorter(the_data,"numeric");</lang>