Data commit

Task/Topic-variable/00-META.yaml

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+---
+from: http://rosettacode.org/wiki/Topic_variable

Task/Topic-variable/00-TASK.txt

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+Several programming languages offer syntax shortcuts to deal with the notion of "current" or "topic" variable.
+
+A topic variable is a [[Special variables|special variable]] with a very short name which can also often be omitted.
+
+Demonstrate the utilization and behaviour of the topic variable within the language and explain or demonstrate how the topic variable behaves under different levels of nesting or scope, if this applies, within the language.
+
+For instance you can (but you don't have to) show how the topic variable can be used by assigning the number <math>3</math> to it and then computing its square and square root.
+<br><br>
+

Task/Topic-variable/AppleScript/topic-variable-1.applescript

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+on run
+    1 + 2
+
+    ap({square, squareRoot}, {result})
+
+    --> {9, 1.732050807569}
+end run
+
+
+-- square :: Num a => a -> a
+on square(x)
+    x * x
+end square
+
+-- squareRoot :: Num a, Float b => a -> b
+on squareRoot(x)
+    x ^ 0.5
+end squareRoot
+
+
+-- GENERIC FUNCTIONS ----------------------------------------------------------
+
+-- A list of functions applied to a list of arguments
+-- (<*> | ap) :: [(a -> b)] -> [a] -> [b]
+on ap(fs, xs)
+    set lst to {}
+    repeat with f in fs
+        tell mReturn(contents of f)
+            repeat with x in xs
+                set end of lst to |λ|(contents of x)
+            end repeat
+        end tell
+    end repeat
+    return lst
+end ap
+
+-- Lift 2nd class handler function into 1st class script wrapper
+-- mReturn :: Handler -> Script
+on mReturn(f)
+    if class of f is script then
+        f
+    else
+        script
+            property |λ| : f
+        end script
+    end if
+end mReturn

Task/Topic-variable/AppleScript/topic-variable-2.applescript

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+on run
+    script
+        -- The given function applied to the value 3
+        on |λ|(f)
+            mReturn(f)'s |λ|(3)
+        end |λ|
+    end script
+
+    -- Here, 'result' is bound to the script above
+    map(result, {square, squareRoot})
+
+    --> {9, 1.732050807569}
+end run
+
+
+-- square :: Num a => a -> a
+on square(x)
+    x * x
+end square
+
+-- squareRoot :: Num a, Float b => a -> b
+on squareRoot(x)
+    x ^ 0.5
+end squareRoot
+
+
+-- GENERIC FUNCTIONS ----------------------------------------------------------
+
+-- map :: (a -> b) -> [a] -> [b]
+on map(f, xs)
+    tell mReturn(f)
+        set lng to length of xs
+        set lst to {}
+        repeat with i from 1 to lng
+            set end of lst to |λ|(item i of xs, i, xs)
+        end repeat
+        return lst
+    end tell
+end map
+
+-- Lift 2nd class handler function into 1st class script wrapper
+-- mReturn :: Handler -> Script
+on mReturn(f)
+    if class of f is script then
+        f
+    else
+        script
+            property |λ| : f
+        end script
+    end if
+end mReturn

Task/Topic-variable/Axe/topic-variable.axe

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+3
+Disp *3▶Dec,i

Task/Topic-variable/BASIC256/topic-variable.basic

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+function Sum (x, y)
+    Sum = x + y  # using name of function
+end function
+
+function SumR (x, y)
+    return x + y  # using Return keyword which always returns immediately
+end function
+
+print Sum (1, 2)
+print SumR(2, 3)

Task/Topic-variable/Clojure/topic-variable.clj

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+user=> 3
+3
+user=> (Math/pow *1 2)
+9.0
+user=> (Math/pow *2 0.5)
+1.7320508075688772

Task/Topic-variable/Forth/topic-variable-1.fth

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+: myloop 11 1 do i . loop cr ; myloop

Task/Topic-variable/Forth/topic-variable-2.fth

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+: ^2 dup * ;
+: sqrt 0 tuck ?do 1+ dup 2* 1+ +loop ;
+: topic >r r@ ^2 . r@ sqrt . r> drop ;
+
+23 topic

Task/Topic-variable/FreeBASIC/topic-variable.basic

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+' FB 1.05.0 Win64
+
+' Three different ways of returning a value from a function
+
+Function Sum (x As Integer, y As Integer) As Integer
+  Sum = x + y  '' using name of function
+End Function
+
+Function Sum2 (x As Integer, y As Integer) As Integer
+  Function = x + y  '' using Function keyword
+End Function
+
+Function Sum3 (x As Integer, y As Integer) As Integer
+  Return x + y  '' using Return keyword which always returns immediately
+End Function
+
+Print Sum (1, 2)
+Print Sum2(2, 3)
+Print Sum3(3, 4)
+Sleep

Task/Topic-variable/Go/topic-variable.go

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+package main
+
+import (
+    "math"
+    "os"
+    "strconv"
+    "text/template"
+)
+
+func sqr(x string) string {
+    f, err := strconv.ParseFloat(x, 64)
+    if err != nil {
+        return "NA"
+    }
+    return strconv.FormatFloat(f*f, 'f', -1, 64)
+}
+
+func sqrt(x string) string {
+    f, err := strconv.ParseFloat(x, 64)
+    if err != nil {
+        return "NA"
+    }
+    return strconv.FormatFloat(math.Sqrt(f), 'f', -1, 64)
+}
+
+func main() {
+    f := template.FuncMap{"sqr": sqr, "sqrt": sqrt}
+    t := template.Must(template.New("").Funcs(f).Parse(`. = {{.}}
+square: {{sqr .}}
+square root: {{sqrt .}}
+`))
+    t.Execute(os.Stdout, "3")
+}

Task/Topic-variable/Haskell/topic-variable.hs

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+Prelude> [1..10]
+[1,2,3,4,5,6,7,8,9,10]
+Prelude> map (^2) it
+[1,4,9,16,25,36,49,64,81,100]

Task/Topic-variable/J/topic-variable-1.j

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+   example=: *:, %:  NB. *: is square, %: is square root
+   example 3
+9 1.73205

Task/Topic-variable/J/topic-variable-2.j

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+   Example=: verb def '(*: y), (%: y)'
+   Example 3
+9 1.73205

Task/Topic-variable/J/topic-variable-3.j

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+   (*:, %:) 3
+9 1.73205

Task/Topic-variable/Julia/topic-variable.julia

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+julia> 3
+3
+julia> ans * ans, ans - 1
+(9, 2)

Task/Topic-variable/Kotlin/topic-variable.kotlin

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+// version 1.1.2
+
+fun main(args: Array<String>) {
+    3.let {
+        println(it)
+        println(it * it)
+        println(Math.sqrt(it.toDouble()))
+    }
+}

Task/Topic-variable/Nim/topic-variable-1.nim

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+for _ in 1..10:
+  echo "Hello World!"

Task/Topic-variable/Nim/topic-variable-2.nim

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+import sequtils
+let x = [1, 2, 3, 4, 5]
+let y = x.mapIt(it * it)
+echo y    # @[1, 4, 9, 16, 25]

Task/Topic-variable/Oforth/topic-variable.fth

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+3 dup sq swap sqrt

Task/Topic-variable/PARI-GP/topic-variable.parigp

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+3
+[sqrt(%),%^2]

Task/Topic-variable/Perl/topic-variable-1.pl

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+print sqrt . " " for (4, 16, 64)

Task/Topic-variable/Perl/topic-variable-2.pl

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+for (1..2) {
+  print "outer $_:\n";
+  local $_;
+  for (1..3) {
+    print " inner $_,";
+  }
+  print " fini\n";
+}

Task/Topic-variable/Phix/topic-variable.phix

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+(phixonline)-->
+ <span style="color: #008080;">with</span> <span style="color: #008080;">javascript_semantics</span>
+ <span style="color: #004080;">object</span> <span style="color: #000000;">_</span>
+ <span style="color: #000000;">_</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">3</span>
+ <span style="color: #0000FF;">?</span><span style="color: #000000;">_</span>
+ <span style="color: #0000FF;">?</span><span style="color: #000000;">_</span><span style="color: #0000FF;">*</span><span style="color: #000000;">_</span>
+<!--

Task/Topic-variable/PicoLisp/topic-variable-1.l

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+PicoLisp sets the value of the variable (symbol) '@' to the result of
+conditional and controlling expressions in flow- and logic-functions (cond, if,
+and, when, while, etc.).
+
+Within a function or method '@' behaves like a local variable, i.e. its value is
+automatically saved upon function entry and restored at exit.
+
+For example, to read the current input channel until EOF, and print the square
+of every item which is a number:

Task/Topic-variable/PicoLisp/topic-variable-2.l

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+(while (read)
+   (when (num? @)
+      (println (* @ @)) ) )
+abc   # Not a number
+7     # Number
+49    # -> print square
+xyz   # Not a number
+3     # Number
+9     # -> print square

Task/Topic-variable/PowerShell/topic-variable-1.psh

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+65..67 | ForEach-Object {$_ * 2}     # Multiply the numbers by 2
+65..67 | ForEach-Object {[char]$_ }  # ASCII values of the numbers

Task/Topic-variable/PowerShell/topic-variable-2.psh

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+65..67 | Where-Object {$_ % 2}

Task/Topic-variable/PowerShell/topic-variable-3.psh

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+65..70 | Format-Wide {$_} -Column 3 -Force

Task/Topic-variable/Python/topic-variable.py

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+>>> 3
+3
+>>> _*_, _**0.5
+(9, 1.7320508075688772)
+>>>

Task/Topic-variable/REXX/topic-variable.rexx

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+/*REXX program shows something close to a  "topic variable" (for functions/subroutines).*/
+parse arg N                                      /*obtain a variable from the cmd line. */
+call  squareIt N                                 /*invoke a function to square da number*/
+say   result       '  ◄───'                      /*display returned value from the func.*/
+exit 0                                           /*stick a fork in it,  we're all done. */
+/*──────────────────────────────────────────────────────────────────────────────────────*/
+squareIt:  return  arg(1) ** 2                   /*return the square of passed argument.*/

Task/Topic-variable/Racket/topic-variable.rkt

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+#lang racket
+
+(module topic1 racket
+  ;; define $ as a "parameter", but make it look like a plain identifier
+  (provide $ (rename-out [$if if] [$#%app #%app]))
+  (define current-value (make-parameter #f))
+  (define-syntax $
+    (syntax-id-rules (set!)
+      [(_ x ...) ((current-value) x ...)]
+      [(set! _ val) (current-value val)]
+      [_ (current-value)]))
+  ;; make an `if' form that binds it to the condition result
+  (define-syntax-rule ($if C T E)
+    (parameterize ([current-value C])
+      (if $ T E)))
+  ;; function application with []s uses the topic variable for the first arg
+  (define-syntax ($#%app stx)
+    (syntax-case stx ()
+      [(_ f x y ...) (equal? #\[ (syntax-property stx 'paren-shape))
+       #'(parameterize ([current-value x]) (f y ...))]
+      [(_ f x ...) #'(f x ...)])))
+
+(module topic2 racket
+  ;; better variant: define `$' as a syntax parameter, which is adjusted to an
+  ;; actual local binding; make it work in `if', and have a function definition
+  ;; form that binds it to the actual arguments
+  (provide $ (rename-out [$if if]) defun)
+  (require racket/stxparam)
+  (define-syntax-parameter $ (λ(stx) (raise-syntax-error '$ "not in scope")))
+  (define-syntax-rule ($if C T E)
+    (let ([c C]) (syntax-parameterize ([$ (make-rename-transformer #'c)])
+                   (if c T E))))
+  (define-syntax-rule (defun name body ...)
+    (define (name arg)
+      (syntax-parameterize ([$ (make-rename-transformer #'arg)])
+        body ...)))
+  )
+
+(module sample1 racket
+  (require (submod ".." topic1))
+  (if (memq 2 '(1 2 3)) (cadr $) 'missing)
+  ;; => 3
+  (define (foo) (list (sqrt $) (* $ $)))
+  [foo 9]
+  ;; => '(3 81)
+  )
+(require 'sample1)
+
+(module sample2 racket
+  (require (submod ".." topic2))
+  (if (memq 2 '(1 2 3)) (cadr $) 'missing)
+  ;; => 3
+  (defun foo (list (sqrt $) (* $ $)))
+  (foo 9)
+  ;; => '(3 81)
+  )
+(require 'sample2)

Task/Topic-variable/Raku/topic-variable.raku

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+$_ = 'Outside';
+for <3 5 7 10> {
+    print $_;
+    .³.map: { say join "\t", '', $_, .², .sqrt, .log(2), OUTER::<$_>, UNIT::<$_>  }
+}

Task/Topic-variable/Ring/topic-variable.ring

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+see "sum1 = " + sum1(1,2) + nl
+see "sum2 = " + sum2(2,3) + nl
+
+func sum1 (x, y)
+     sum = x + y
+     return sum
+
+func sum2 (x, y)
+     return x + y

Task/Topic-variable/Ruby/topic-variable-1.rb

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+while DATA.gets     # assigns to $_ (local scope)
+  print             # If no arguments are given, prints $_
+end
+__END__
+This is line one
+This is line two
+This is line three

Task/Topic-variable/Ruby/topic-variable-2.rb

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+DATA.gets
+p [$_.to_i ** 2, Math.sqrt($_.to_i)]        #=> [9, 1.7320508075688772]
+__END__
+3

Task/Topic-variable/Scala/topic-variable.scala

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+object TopicVar extends App {
+  class SuperString(val org: String){
+    def it(): Unit = println(org)
+  }
+
+  new SuperString("FvdB"){it()}
+  new SuperString("FvdB"){println(org)}
+
+  Seq(1).foreach {println}
+  Seq(2).foreach {println(_)}
+  Seq(4).foreach { it => println(it)}
+  Seq(8).foreach { it => println(it + it)}
+}

Task/Topic-variable/Sidef/topic-variable.sidef

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+say [9,16,25].map {.sqrt};   # prints: [3, 4, 5]

Task/Topic-variable/Standard-ML/topic-variable.ml

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+- 3.0;
+val it = 3.0 : real
+- it * it;
+val it = 9.0 : real
+- Math.sqrt it;
+val it = 3.0 : real
+-

Task/Topic-variable/Tailspin/topic-variable.tailspin

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+3 -> \($-1! $+1!\) -> $*$ -> [$-1..$+1] -> '$;
+' -> !OUT::write

Task/Topic-variable/UNIX-Shell/topic-variable.sh

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+multiply 3 4    # We assume this user defined function has been previously defined
+echo $?    # This will output 12, but $? will now be zero indicating a successful echo

Task/Topic-variable/Wren/topic-variable.wren

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+var T // global scope
+
+var doSomethingWithT = Fn.new { [T * T, T.sqrt] }
+
+T = 3
+System.print(doSomethingWithT.call())

Task/Topic-variable/Zkl/topic-variable.zkl

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+a,_,c:=List(1,2,3,4,5,6) //-->a=1, c=3, here _ is used as "ignore"
+3.0 : _.sqrt() : println(_) //-->"1.73205", _ (and :) is used to "explode" a computation
+                            // as syntactic sugar
+1.0 + 2 : _.sqrt() : _.pow(4)  // no variables used, the compiler "implodes" the computation
+    // --> 9