On 21.01.2011, at 09:41, Axel Simon wrote:
Hi,
following the discussion on the ghc mailing list, I propose that the
new "RelaxedLayout" extension that is proposed for ghc 7.1 should be
incorporated into the language standard.
Sorry, this should read "NondecreasingIndentation".
Axel
The motivation is that ghc <7.1 have silently implemented the
"RelaxedLayout" by default and that removing this feature will break
many programs without any gain except that ghc complies to the
standard. Hence, it would be better that the standard is adjusted,
as this would imply no changes to current ghc compilers nor user
programs.
As I'm not familiar with the technical details, I can only give an
idea about what "RelaxedLayout" does. Haskell 2010 would parse
foo = do
some computation
trace "hello" $ do
other computation
such that "other computation" belongs to the first "do", i.e.
foo = do
{ some computation
; trace "hello" $ do
; other computation
}
which leads to a parse error since the second "do" not followed by
any instructions. The relaxed layout extension opens a new block
after a "do" if the next line commences on in the same column as the
current block. Thus, it would parse the example above as:
foo = do
{ some computation
; trace "hello" $ do
{ other computation
}
}
Observations:
- the proposal has been implemented in ghc for years
- it does not break any existing programs (as far as I can see)
- incorporating this proposal into the standard involves no
implementation effort for the ghc compiler nor any program that
compiles with ghc
Cheers,
Axel
_______________________________________________
Haskell-prime mailing list
Haskell-prime@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-prime
_______________________________________________
Haskell-prime mailing list
Haskell-prime@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-prime
