On 03/09/2012 06:37 PM, rob cook wrote:
That is, without using a macro or eval. Id like to do:
(define a 4)
(define l1 '(1 2 3))
(match l1
(`(1 2 ,a) #t)
(_ #f))
So that this example would result in #f, and #t if a bound to 3.
Since of course match has its own quasiquote behavior, this does not
seem possible w/o making a macro for "dynamic" match, or building the
s-exp and using eval (yuck!).
Is this correct, or have I missed something obvious?
It looks like what you're trying to do is to match a particular value
which just so happens to be built using a quasiquote expression. The
right way to do it is with the == match expander:
(define a 4)
(define l1 '(1 2 3))
(match l1
((== `(1 2 ,a)) #t)
(_ #f)) ; -> #f
You can also put any other expression there:
(match l1
((== (append (take l1 2) (list (sub1 a)))) #t)
(_ #f)) ;-> #t
Or use a different comparison predicate:
(match l1
((== `(1 2 ,(sub1 a)) eq?) #t)
(_ #f)) ; -> #f
Hope that helps!
--
Brian Mastenbrook
br...@mastenbrook.net
http://brian.mastenbrook.net/
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