#4359: Implement lambda-case/lambda-if
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Reporter: batterseapower | Owner:
Type: feature request | Status: new
Priority: normal | Milestone: 7.4.1
Component: Compiler | Version: 7.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by simonmar):
Replying to [comment:31 claus]:
> Some of the syntax suggestions here scare me. But even if an
unproblematic syntax could be found, do you really want to add a complex
language construct with limited usage pattern?
I'm really surprised by both "complex language construct" and "limited
usage pattern" here, since those are both issues that I thought the
proposal addresses quite well.
* complex: we're re-using existing syntax and translations. The
specification should be entirely straightforward (thought admittedly I
haven't tried writing it down yet). The syntax is consistent with the
rest of the language; it seems to me a natural generalisation. It's just
an anonymous version of multi-equation function definitions, and the
syntax is exactly what you'd expect.
* limited usage pattern: it covers all the use cases that came up in the
discussion: lambda-case, lambda-if (both with multiple arguments) and also
`mcase` and `mif`.
> While I'm here: have you looked at [http://hackage.haskell.org/trac
/haskell-prime/ticket/114 introduce lambda-match (explicit match failure
and fall-through)], from around the same time as lambda-case? At the time,
it was implemented as a small parser modification, with most of the
functionality in a library (see [http://hackage.haskell.org/trac/haskell-
prime/ticket/114#attachments ticket attachments] for patch, library, and
some examples), and 'case'-as-a-function was easy to implement in terms of
it. But it also supported other useful programming patterns.
Yes, I remember it, though I'd have to go and review the discussion to
fully understand the motivation. On the face of it the syntax looks a bit
strange (vertical bar is re-used).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4359#comment:33>
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