#2798: Enable "rec" keyword when RecursiveDo is enabled?
---------------------------------+------------------------------------------
Reporter: nominolo | Owner:
Type: task | Status: new
Priority: normal | Component: Compiler
Version: 6.11 | Severity: minor
Keywords: | Testcase:
Architecture: Unknown/Multiple | Os: Unknown/Multiple
---------------------------------+------------------------------------------
GHC supports recursive statement groups marked by the keyword {{{rec}}},
however this is only activated via a hack. Consider this (silly) example
program:
{{{
{-# LANGUAGE RecursiveDo, Arrows #-}
main :: IO ()
main =
mdo x <- return (length [1..42::Int])
rec b <- return x
let a = const c
c <- print "x"
return (a b)
}}}
The {{{Arrow}}} language needs to be enabled, otherwise the {{{rec}}}
keyword wouldn't be recognised. Currently this behaviour is undocumented,
and {{{rec}}} groups only appear in the internal AST.
This ticket has been created to have a documented decsion whether this
feature is supported or not. Given that GHC automatically identifies
strongly-connected components and re-groups things (although it cannot re-
order statements due to probable dependencies) having an explicet
{{{rec}}} keyword probably isn't that useful. In particular
{{{
mdo foo ...is equivalent to... mdo rec foo
bar bar
baz baz
}}}
Thoughts?
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2798>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler_______________________________________________
Glasgow-haskell-bugs mailing list
Glasgow-haskell-bugs@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
