rslt ← {larg} I ##._fk J fk_ K rarg ⍝ simulation of "fork" syntax. rslt ← {larg} I ##.fk J fk K rarg ⍝ slower but more elegant. NB: forks are now implemented as primitive constructs in Dyalog. The function '≥' (greater than or equal) can be considered to be the application of the two functions '>' (greater than) and '=' (equal), separately between the arguments and the combining of the results with '∨' (or). ┌───∨───┐ ┌─>─┐ ┌─=─┐ ⍺ ⍵ ⍺ ⍵ Suggested by Phil Last, fork implements this tree structure using a pair of op- erators [_fk] and [fk_]. An alternative coding --------------------- Phil goes on to say: The version below I wrote last year when I was thinking about the technique I used in →cond←, where the need for the separation and interdependence is swapped for the loss of a very few fairly unlikely scalar arguments (and several extra lines of code). fk←{ A B C←112358314594370 774156178538190 998752796516730 ⍺←A ⍝ ⍺←A ⋄ fg←f←⍺⍺ ⋄ h←g←⍵⍵ ⍺≡A:B ⍺⍺ ⍵(⍵⍵ ⍵) ⍝ ⍺≡A:B fg ⍵(h ⍵) ⍺≡B:⊃⍺⍺{(⍺⍺ ⍺)⍵⍵ ⍵}⍵⍵/⍵ ⍝ ⍺≡B:⊃{(f ⍺)g ⍵}/⍵ ⍺≡C:⊃⍺⍺{(⊃⍺⍺/⍺)⍵⍵ ⍵}⍵⍵/⍵ ⍝ ⍺≡C:⊃{(⊃f/⍺)g ⍵}/⍵ C ⍺⍺(⍺ ⍵)(⍺ ⍵⍵ ⍵) ⍝ C fg(⍺ ⍵)(⍺ h ⍵) } It's slower than the _fk/fk_ pair obviously improving relatively as the overhead gets less significant ... (>fk∨fk=)cf(>_fk∨fk_=)∘⌽⍨⍳1e1 2.292270531 (>fk∨fk=)cf(>_fk∨fk_=)∘⌽⍨⍳1e3 1.798882682 (>fk∨fk=)cf(>_fk∨fk_=)∘⌽⍨⍳1e6 0.9954407295 at which point it's only twice as slow as the primitive ... (>fk∨fk=)cf≥∘⌽⍨⍳1e6 2.006006006 So it's only an exercise in coding but it's a better model if we ever decided to add a primitive. It even extends correctly to odd trains (forks of forks) which _fk/fk_ doesn't ... The following is true for boolean arguments (≥ ←→ ∨∘~ ←→ if) each time replacing the leftmost function with an equivalent fork ... ≥ ←→ >fk∨fk= ←→ =fk⍱fk<fk∨fk= ←→ ∧fk∨fk⍱fk⍱fk<fk∨fk= ∘.(∧fk∨fk⍱fk⍱fk<fk∨fk=)⍨0 1 1 0 1 1 NB: In Dyalog operator-operand sequences associate (bind) left, so that: f op g op h ←→ (f op g)op h whereas, in J, forks associate right: f g h ←→ f(g h) This difference is reflected in this implementation of fork. Examples: ge ← > _fk ∨ fk_ = ⍝ defined ≥ function (dyadic). (⍳5) ∘.ge ⍳5 1 0 0 0 0 1 1 0 0 0 1 1 1 0 0 1 1 1 1 0 1 1 1 1 1 mean ← +/ _fk ÷ fk_ ⍴ ⍝ arithmetic mean (monadic). mean 1 2 3 4 2.5 See also: dft cond co_ops Back to: contents Back to: Workspaces