#3674: Recognise language pragmas generated by custom pre-processors (run with
-F)
---------------------------------+------------------------------------------
Reporter: dorchard | Owner: dorchard
Type: feature request | Status: new
Priority: normal | Component: Compiler
Version: | Keywords: customer pre-processor
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: GHC rejects valid program
---------------------------------+------------------------------------------
A custom pre-processor might desugar terms into terms of a particular
language extension, requiring a new language pragma.
Currently, any language pragmas generated by a pre-processor will be
ignored once the pre-processed file is picked up by GHC again.
As a contrived example, consider foo.hs:
{{{
{-# OPTIONS -F -pgmF ./preprocess.sh #-}
data Foo a where MkFoo :: Foo a
}}}
where preprocess.sh:
{{{
#!/bin/sh
( echo "{-# LANGUAGE GADTs #-}"; cat $2; ) > $3
}}}
Currently we get this behaviour:
{{{
bash-3.2$ ghc foo.hs
/tmp/ghc7191_0/ghc7191_0.hspp:4:0:
Illegal generalised algebraic data declaration for `Foo'
(Use -XGADTs to allow GADTs)
In the data type declaration for `Foo'
bash-3.2$ ghc foo.hs -E
bash-3.2$ cat foo.hspp
{-# LANGUAGE GADTs #-}
{-# OPTIONS -F -pgmF ./preprocess.sh #-}
data Foo a where MkFoo :: Foo abash-3.2$
}}}
It would be nice if GHC noticed the new pragmas, particularly language
pragmas, although perhaps not all pragmas should be picked up (maybe not
new OPTION pragmas).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3674>
GHC <http://www.haskell.org/ghc/>
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