On July 15, 2013 at 6:30:28 PM, Daniel Dinnyes (dinny...@gmail.com) wrote:
Hmm, good point, especially the `let` one... What is `as->`? I can't find
anything about that.
http://clojure.github.io/clojure/clojure.core-api.html#clojure.core/as-%3E
There is one benefit over `let` though: it is more explicit. Let allows you to
define independent bindings mixed together with multiple threads of dependent
bindings (which can be mixed in random combinations). As the number of bindings
increase it becomes quite messy, and hard to decipher which line depends on
which. I have seen, even written myself (shame on me), such code. I feel that
this is the main reason for the `core` threading macros too ("why not use let
instead?" would still apply then). On the other hand as my simple example code
demonstrates (off the top of my hat, cuz ya need to show da code!), in a
functional language the parameter order shouldn't matter, and there shouldn't
be privileged (main!?) parameter positions (Clojure is the landguage of
multimethods after all!)
Your ->>> is a bit awkward because the symbol to the left represents the value
of the previous expression, not the value of the following expression as is the
case with most "bindings forms" in Clojure. Also, as-> simplifies your use case
by only needing to identify one name that is used in all the threaded forms.
Honestly, if I'm going to do anything more complicated that as->, I would
rethink how I want to express my code.
Anyway, I see the reason for -> and ->> macros and indeed the first and last
positions are special in some sense. The -> is good for navigating protocols,
and ->> is good for functions expected/designed to be partially applied. Is
that correct?
The threading macros operate on the forms directly, so I'm not sure what you
mean by "partially applied" here. The big win for ->> is that the sequence
functions in Clojure core expect the sequence to be last. This is handy for
threading a sequence through multiple transformations.
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