match ( branches -- quot )
Algebraic data types

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variant-class

Vocabulary
variants

Inputs

branches

an array

Outputs
None

Word description
Dispatches on the type of the value on the top of the stack. If the type is a singleton-class, the corresponding quotation is called with the underlying stack unchanged. If the type is a tuple-class, the tuple slots are pushed onto the stack by order of arguments.

Examples

USING: kernel math prettyprint variants ; IN: scratchpad VARIANT: list nil cons: { { first object } { rest list } } ; : list-length ( list -- length ) { { nil [ 0 ] } { cons [ nip list-length 1 + ] } } match ; 1 2 3 4 nil <cons> <cons> <cons> <cons> list-length .
4

See also
VARIANT:, variant-class

Definition

USING: arrays combinators kernel quotations sequences ;

IN: variants

MACRO: match ( branches -- quot )
    [ dup callable? [ first2 (match-branch) 2array ] unless ]
    map [ \ dup \ ?class ] dip \ case [ ] 4sequence ;