Proposal: Left-Associative Semigroup Operator Alias in "Data.Semigroup"

[Tikhon Jelvis]

Are there other use cases where the left-associative operator enables nicer
code? I suspect that they are, but I can't think of any myself.

On Mon, Jun 6, 2016 at 6:45 AM, Mario Blažević <mblazevic at stilo.com> wrote:

> On 2016-06-06 07:30 AM, Herbert Valerio Riedel wrote:
>
>> Hello!
>>
>> In short, the right-associative fixity of (Data.{Monoid,Semigroup}.<>)
>> subtly conflicts with definitions of (<>) in pretty printing APIs, for
>> which the left-associative variant is sometimes desirable. This subtle
>> overloading of (<>) is error-prone, as one has to remember which version
>> of (<>) is currently in scope in order to be able to reason about
>> non-trivial expressions involving this operator.
>>
>> This proposal is an attempt to resolve this unfortunate and confusing
>> situation by completing the `Semigroup`/`Monoid` vocabulary with a
>> standard left-associative alias. Please see
>>
>>    https://ghc.haskell.org/trac/ghc/wiki/Proposal/LeftAssocSemigroupOp
>>
>> for more details.
>>
>> Discussion period: 4 weeks
>>
>>
>>
>         The proposal is well argued, but it omits any discussion of the
> proper place for the new operator. Why place it in Data.Semigroup, if its
> only purpose is to support the pretty-print libraries? Since the libraries
> in question will need to change anyway, or at least their imports will, why
> not add the operator there instead? Or, alternatively, to a
> Text.PrettyPrint module?
>
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