You could also imagine a parsing of where, where the following would be the
way to write this:
f tree =
case tree of
Leaf x ->
munge a b
where
b = ...
Node s t ->
munge a c
where
c = ...
where
a = ...
On Tuesday, January 3, 2017 at 1:26:33 AM UTC-5, Janis Voigtländer wrote:
>
> And do you like that version? It seems to not have the advantages usually
> claimed for "where" in this discussion. For example, you define "a" before
> using it. What about "intent first" here? And in some sense, this
> formulation now looks like a dual to the workaround Joey proposed with
> "let" to please "where" proponents. Isn't it strange that "a" and "work"
> look like they might be mutually recursive now, when they are actually not
> and when the "let"-formulation made that explicitly visible?
>
> Am 02.01.2017 um 23:10 schrieb Colin Woodbury <[email protected]
> <javascript:>>:
>
> @Janis, I suppose the `where` version of that formation would have to be:
>
> f tree = work
> where a = ...
> work = case tree of
> Leaf x -> -- using a and b
>
> where b = ...
> Node s t -> -- using a c
>
> where c = ...
>
>
> On Sunday, 1 January 2017 12:21:47 UTC-8, Janis Voigtländer wrote:
>>
>> Janis, the following compiles for me: …
>>
>> Right, where does not work for expressions, but for right-hand sides, of
>> which pattern match branches are an instance.
>>
>> The next question would be, still under the assumption that a choice has
>> to be made between where and let because both won’t be made available at
>> the same time, how well “where-only” would work if in addition one wants
>> to have a local binding that spans all pattern match branches, i.e.,
>> something one would currently write in Elm like so:
>>
>> f tree =
>> let
>> a = ... something ...
>> in
>> case tree of
>> Leaf x -> let b = ... in ... using a and b ...
>> Node s t -> let c = ... in ... using a and c ...
>>
>>
>>
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