Control structure

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Some modern versions of APL include a set of keywords for controlling flow of execution. Such keywords allow programmers to create control structures which are commonly used in procedural programming languages.

Example

Dyalog APL has a rich set of flow control keywords, including :If, :While, :Repeat, :For (with the supplementary control words :In and :InEach), :Select, :With, :Trap, :Hold and :Disposable. The use of control structures defined by these keywords is only allowed in defined functions.

For example, a function implementing the Trabb Pardo–Knuth algorithm using control structures:

∇ {res}←trabb;f;S;i;a;y
  f←{(0.5*⍨|⍵)+5×⍵*3}
  S←,⍎{⍞←⍵ ⋄ (≢⍵)↓⍞}'Please, enter 11 numbers: '
  :For i a :InEach (⌽⍳≢S)(⌽S)
      :If 400<y←f(a)
          ⎕←'Too large: ',⍕i
      :Else
          ⎕←i,y
      :EndIf
  :EndFor
∇

External links

Tutorials

Documentation

APL syntax [edit]
General Comparison with traditional mathematicsPrecedenceTacit programming (Train, Hook, Split composition)
Array Numeric literalStringStrand notationObject literalArray notation (design considerations)
Function ArgumentFunction valenceDerived functionDerived operatorNiladic functionMonadic functionDyadic functionAmbivalent functionDefined function (traditional)DfnFunction train
Operator OperandOperator valenceTradopDopDerived operator
Assignment MultipleIndexedSelectiveModified
Other Function axisBracket indexingBranchStatement separatorQuad nameSystem commandUser commandKeywordDot notationFunction-operator overloadingControl structureComment