You could also let every function take a map as input/output.
Then, b could return a map with key :result-b or similar.
This result would then pass through the rest of the functions and be
accessible in e.
Like this:
a ; => {:result-a ...}
b ; => {:result-b ... :result-a ...}
...
d ; => {... :result-a ...}
e ; use :result-a
This technique is brought up in:
http://www.infoq.com/presentations/Thinking-in-Data
Jonathan
On Fri, Oct 26, 2012 at 4:43 AM, Ben Mabey <b...@benmabey.com> wrote:
> On 10/25/12 6:24 PM, Jason Bennett wrote:
>
>>
>> Let's say I have a set of thread-first calls:
>>
>> (-> url
>> a
>> b
>> c
>> d
>> e)
>>
>> And let's say that I need to process and save the result of function b as
>> a second parameter to function e (function b returns a file, and function e
>> needs the extention of that file). How would I drop a let into the middle
>> of the thread calls without making a large mess? The only suggestion I've
>> gotten so far is to move calls A and B into a let before the thread-first
>> so I can process their return values.
>>
>> jason
>>
>
> Pallet's thread-exp library has a let-> macro that would do the trick:
>
> https://github.com/pallet/**thread-expr/blob/develop/src/**
> pallet/thread_expr.clj#L100-**106<https://github.com/pallet/thread-expr/blob/develop/src/pallet/thread_expr.clj#L100-106>
>
> I love the thread-expr library but when I spoke with Hugo Duncan at
> Clojure West he said that pallet's use of it was largely being replaced by
> monads.
>
> -Ben
>
>
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