On Wednesday, April 2, 2014 3:39:47 PM UTC-5, Christopher Howard wrote:
>
> On Wed, 2 Apr 2014 14:07:47 -0600
> Timothy Baldridge <tbald...@gmail.com <javascript:>> wrote:
>
> > I don't know of anything built-in, but this should do the trick:
> >
> > (defn remove-first [f [head & tail]]
> > (if (f head)
> > tail
> > (cons head (lazy-seq (remove-first f tail)))))
> >
> > Timothy
> >
> >
>
> Thanks. This seems to work for my purposes, although I modified it to
> handle the empty vector:
>
> (defn remove-first [f [head & tail]]
> (if (not head) []
> (if (f head)
> tail
> (cons head (lazy-seq (remove-first f tail))))))
>
> This implementation doesn't seem to work on everything that "remove"
> works on:
>
> com.example.myapp=> (remove #(= [1 2] %) {1 2 3 4})
> ([3 4])
> com.example.myapp=> (remove-first #(= [1 2] %) {1 2 3 4})
> UnsupportedOperationException nth not supported on this type:
> PersistentArrayMap clojure.lang.RT.nthFrom (RT.java:835)
>
To fix that, use `seq` on the collection argument. Also, if you want a
emtpy sequence as a result instead of nil, just move the lazy-seq up since
(lazy-seq nil) is an empty sequence.
(lazy-seq (when-let [[head & tail] (seq coll)] ...)
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