Missing some parens there. Should be (->> (take 2)), of course.
On Feb 4, 12:53 pm, Alan <a...@malloys.org> wrote:
> Another solution, which is not especially satisfying but is worth
> considering, is to use the most-common thread style at the top level,
> and interweave some exceptions for the less-common style.
>
> (-> 10
> range 20
> (->> take 2))
> or
> (->> 10
> (#(range % 20))
> (take 2))
>
> On Feb 4, 12:05 pm, B Smith-Mannschott <bsmith.o...@gmail.com> wrote:
>
> > Clojure's threading macros -> and ->> to be quite a win. It breaks
> > down when the expression to be chained together are not consistent in
> > nesting the threaded expression second or last. An idiomatic way to
> > gain the necessary flexibility seems to be via let:
>
> > (let [x (line-seq x)
> > x (sort x)
> > ...]
> > x)
>
> > I've never been very happy with that solution. The same variable
> > appears multiple times in the same let. Maybe that just confuses my
> > Scheme sensibilities. (I know there are previously been discussions
> > about a variant of -> which allows the threading position to be marked
> > in some way, though these never really went anywhere. I also rejected
> > the alternative of using an anaphoric macro which always uses 'it or
> > '$ or some such as the name to thread through. That didn't seem very
> > Clojuresque.)
>
> > I came up with this macro, but I'm unsure what to call it:
>
> > (defmacro thread-let [[varname init-expression :as binding] & expressions]
> > {:pre [(symbol? varname)
> > (not (namespace varname))
> > (vector? binding)
> > (= 2 (count binding))]}
> > `(let [~@(interleave (repeat varname) (cons init-expression expressions))]
> > ~varname))
>
> > usage example:
>
> > (thread-let [x (initial-value)]
> > (foo x 3)
> > (bar 1 2 x))
>
> > which is equivalent to:
>
> > (let [x (initial-value)
> > x (foo x 3)
> > x (bar 1 2 x)]
> > x)
>
> > What should I name this thing? I'm concerned that "thread" is
> > confusing due to its dual meaning. let seems in line with clojure
> > conventions.
>
> > (thread-let [x ...] ...)
> > (thread-with [x ...] ...)
> > (thread-through [x ...] ...)
> > (let-> [x ...] ...)
>
> > thoughts?
>
> > // Ben
>
>
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