cache ( ... key assoc quot: ( ... key -- ... value ) -- ... value )
Factor handbook » The language » Collections » Associative mapping operations » Associative mapping combinators

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Vocabulary
assocs

Inputs

key	a key
assoc	an assoc
quot	a quotation with stack effect ( ... key -- ... value )

Outputs

value

a previously-retained or freshly-computed value

Word description
If the key is present in the assoc, outputs the associated value, otherwise calls the quotation to produce a value and stores the key/value pair into the assoc. Returns a value either looked up or newly stored in the assoc.

Side effects
Modifies assoc

Definition

USING: kernel ;

IN: assocs

: cache
    ( ... key assoc quot: ( ... key -- ... value ) -- ... value )
    [ [ at* ] 2keep ] dip
    [ [ nip call dup ] [ drop ] 3bi set-at ] 3curry
    [ drop ] prepose unless ; inline