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SketchyLISP
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  Copyright (C) 2007
Nils M Holm

assoc

Conformance: R5RS Scheme

Purpose: Retrieve an association from an association list. An association list is a list of pairs where the car part of each pair holds a key and the cdr part of the pair holds the value associated with that key:
((key1 . value1) ... (keyN . valueN))
Assoc returns the first association whose key is equal to a given datum.

Arguments:
X - key of value to be found
A - association list

Implementation:

(define (assoc x a)
  (cond ((null? a) #f)
    ((equal? (caar a) x) (car a))
    (else (assoc x (cdr a)))))

Example:

(assoc '3 '((1 . i) (2 . ii) (3 . iii) (4 . iv))) 
=> (3 . iii)

See also:
assv, assq, member.