ForLoop

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To code a for-loop (see pseudo-code below) in which y is the primary argument to the loop and each iteration runs dyadic function f between y and item x of vector v of data items (a b c d ...) in the given order. At each iteration f is to return a modification of y or another array in the same domain as y as input to the next iteration or finally as the result:

   FOR x IN a b c d ...
      y←x f y
   END

Here it is:

      ⊃f/(⌽V),⊂Y                  ⍝ V←AV; Y←AA

That's it. That's the APL way. The array oriented way. No need for control structures. No need for branches. No need to execute artificially contructed diamond strewn statements. It's what reduction is.

Examples

      ⎕FX⍕2 1⍴'r←av(f ForLoop)aa' 'r←⊃f/(⌽av),⊂aa'
      2 ¯2 1↓ForLoop 'lose' 'these' 'and this' 'keep' 'these' 'three' 'forget' 'these'
 keep  these  three
      (⍳4)+ForLoop 2 5⍴⍳10
 6  7  8  9 10
11 12 13 14 15
      ⎕fx⍕2 1⍴'r←tv rep cv' 'r←((1⊃tv),cv)[(cv≠0⊃tv)×1+⍳⍴⎕←cv]'
      'ts' rep 'heart'
heart
hears
      'ts' 'hf' 'rt' 'ei' 'as' rep ForLoop 'heart'
heart
hears
fears
feats
fiats
fists

Specialities

Some APLs include control structures specifically to emulate the pseudo-code above. This can offer optimisation opportunities for the interpreter; it also allows the APL editor to indent code for clarity, and to check for unbalanced control structures. However, opinion is divided within the APL programming community about which approach is preferable.

Compatibility

Checked with: APL2, APLX, Dyalog, NARS2000 APL+Win, - Add as many as you can/like

Test Cases

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Test
 ⎕IO←0      ⍝ You may change this; however, zero IS the default in the Phrasebook
⍝⎕ML←3      ⍝ Enable this line in Dyalog APL if appropriate
 ⎕FX'r←[larg] PhraseName rarg' 'r←phrase'
⍝ ---- Start Test cases (do not delete this!)
 /* expectedResult ≡ statement */

Test my code, both Examples and Test Cases.

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