Currying in GNU APL

Question

I was trying to "curry" a function in GNU APL, however it doesn't seem to work?

For example:

      (1∘+) 1
SYNTAX ERROR
      (1∘+)1
      ^   ^

What am I doing wrong? Is ∘ the wrong glyph to use?

Answer 1

GNU APL does not have the Bind meaning of ∘, found in Dyalog and related implementations. Instead, the ∘ glyph is exclusively used for the outer product notation, ∘.f.

However, you can define a reasonable substitute yourself:

∇ r←(a o b)z
  →3⌊⎕NC'b'
  r←z a b ⋄ →0
  r←a b z
∇

It can be used almost like the primitive, except requiring a space when adjacent to a name on its left or a non-glyph on its right:

      (1o+) 1
2
      (+o 1) 1
2
      1o+ 1
2

---

Note that the above substitute does not provide function composition. In order to also include this, we have to go for a more involved definition:

∇ r←x(a o b)y  ⍝ ∘
  →2⌈¯5+2⊥3⌊⎕NC⍪'ab'
  r←a b y ⋄ →0 ⍝ A∘f
  r←y a b ⋄ →0 ⍝ f∘B
  ⍎'x←{⍵}'/⍨0=⎕NC'x'
  r←x a b y    ⍝ f∘g
∇

Now everything works:

      (1o+) 1
2
      (+o 1) 1
2
      1o+ 1
2
      1+o|¯1
2