Arguments and Operands

Within a dfn/dop, arguments/operands are referred to by fixed names rather than declared in a header as they are for tradfns/tradops.

• ⍵ is the right argument, and is always available.
• ⍺ is the left argument. A dfn is ambivalent: when it is called monadically, ⍺ has no value until a statement beginning ⍺← supplies a default left argument.

Examples

      {⍵} 5             ⍝ right argument
5
      2 {⍺,⍵} 5         ⍝ both arguments
2 5

A dop refers to its operands:

• ⍺⍺ is the left operand, and is always available.
• ⍵⍵ is the right operand, present only in a dyadic operator.

An operand can be a function or an array.

Example

      -{⍺⍺ ⍵} 5         ⍝ ⍺⍺ is the operand function, here Negate
¯5

A dfn refers to itself as ∇, and a dop as ∇∇, which allows recursion without naming the operation.

Example

      {⍵≤1: 1 ⋄ ⍵×∇ ⍵-1} 5    ⍝ factorial by self-reference
120