Opcode 3: Cell Check

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Opcode 3: Cell Check#

Syntax#

Opcode 3 implements the idiomatic ? wut cell check operator, which tests whether a noun is a cell.

*[a 3 b]            ?*[a b]

Explanation#

Opcode 3 tests whether the product of formula b is a cell or an atom. It returns 0 (yes) if it’s a cell, 1 (no) if it’s an atom.

  1. Evaluate b against the subject to produce a noun.

  2. Test if that noun is a cell.

  3. Return 0 if cell, 1 if atom.

One implication of nouns is that an easy way to tell data apart is by their structure:

?[a b]              0
?a                  1

? wut is useful to ask whether a given noun is a cell or an atom. (Like C’s int main() return type and error codes, 0 means TRUE and 1 means FALSE.)

(Opcode 5 is closely related, as it tests whether one noun is equal to another.)

Opcode 3 is used for type discrimination (by structure before pattern matching) and for validating noun data shapes.

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