On Sat, Feb 21, 2009 at 1:34 PM, Frantisek Sodomka <fsodo...@gmail.com> wrote:
>
> nth claims to also work on regex Matchers:
>
> user=> (doc nth)
> -------------------------
> clojure.core/nth
> ([coll index] [coll index not-found])
> Returns the value at the index. get returns nil if index out of
> bounds, nth throws an exception unless not-found is supplied. nth
> also works for strings, Java arrays, regex Matchers and Lists, and,
> in O(n) time, for sequences.
>
> Please, could somebody show me an example of that? I tried things
> along the lines of:
>
> user=> (re-seq #"a" "ababaa")
> ("a" "a" "a" "a")
> user=> (re-matcher #"a" "ababaa")
> #<Matcher java.util.regex.Matcher[pattern=a region=0,6 lastmatch=]>
> user=> (nth (re-matcher #"a" "ababaa") 0)
> java.lang.IllegalStateException: No match found (NO_SOURCE_FILE:0)
> user=> (seq (re-matcher #"a" "ababaa"))
> java.lang.IllegalArgumentException: Don't know how to create ISeq
> from: Matcher (NO_SOURCE_FILE:0)
>
> ... but no success so far.
Valiant attempts, all. But Matcher is a mutable Java object -- you're
trying to use nth on it before it's been fully initialized. Calling
it's find method (or using the single-arg form of re-find) will cause
it to refer to the first match in the string, at which point nth can
be used to pick out the group you want:
user=> (def m (re-matcher #"(a)(b)" "ababaa"))
#'user/m
user=> (re-find m)
["ab" "a" "b"]
user=> (class m)
java.util.regex.Matcher
user=> (nth m 1)
"a"
I would recommend avoiding using re-matcher or the single-arg re-find
unless you're sure you need the performance or flexibility in some
particular kind of loop. It's much more pleasant to work with re-seq.
--Chouser
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