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olsonjeffery/multirember -- bad

Created May 5, 2011 20:26
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little schemer stuff.. '() vs quote() in racket
Raw
multirember -- bad
(define multirember
(lambda (a lat)
(cond
((null? lat) ('()))
((eq? (car lat) a) (multirember a (cdr lat)))
(else (cons (car lat)
(multirember a (cdr lat)))))))
> (multirember 'jeff '(jeff kerra jeff))
procedure application: expected procedure, given: '() (no arguments)
=== context ===
/Users/jeff/src/racket/ls.rkt:60:2: multirember
/Users/jeff/Racket v5.1/collects/racket/private/misc.rkt:85:7
Raw
multirember -- good
(define multirember
(lambda (a lat)
(cond
((null? lat) (quote()))
((eq? (car lat) a) (multirember a (cdr lat)))
(else (cons (car lat)
(multirember a (cdr lat)))))))
> (multirember 'jeff '(jeff kerra jeff))
'(kerra)
Raw
subst
(define subst2
(lambda (new o1 o2 lat)
(cond
((null? lat) ('()))
(else (cond
((or (eq? (car lat) o1) (eq? (car lat) o2)) (cons new (cdr lat)))
(else (subst2 new o1 o2 (cdr lat))))))))
> (subst 'jeff 'geoff '(geoff kerra geoff))
'(jeff kerra geoff)
@olsonjeffery
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so, basically:

'() == (quote ()) .. too many parens.. interestingly, there are several applications where ('()) works while it doesn't in others. mysteries within mysteries...

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