wiki:AlternativeLayoutRule

Version 1 (modified by igloo, 4 years ago) (diff)

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Proposal: AlternativeLayoutRule

Ticket #134
Dependencies
Related

Compiler support

GHC full (-XAlternativeLayoutRule)
nhc98 none
Hugs none
UHC none
JHC none
LHC none

Summary

A short summary of the extension/modification.

Description

Originally formulated by John Meacham, and a standalone implementation written:

Implemented (with slight differences) in GHC HEAD (6.13) as the AlternativeLayoutRule extension.

One bug, going right back to the original definition, is that

foo = let { x = x } in x

gets translated into

foo = let { x = x } } in x

This needs to be resolved before we can proceed.

Additionally, there has been some discussion as to how the rule should behave exactly. In particular, some people believe that it would be better to keep the rule simple by not doing anything with commas, at the cost of rejecting more H98 code. It would be possible to transition to this, by issuing a warning if the new comma rules are needed.

Some differences between the H98 and this rule are exercised by tests in the layout section of GHC's testsuite.

References

http://www.mail-archive.com/haskell-prime@haskell.org/msg01938.html

darcs get http://repetae.net/repos/getlaid/

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