#4886: GHC "extensions" for (pre/post)processors
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Reporter: pumpkin | Owner:
Type: proposal | Status: new
Priority: normal | Component: Compiler
Version: 7.0.1 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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I've been using Conor McBride's SHE recently and while it's excellent,
error messages produced by code it generates are generally unreadable.
This is because the code preprocessor has no opportunity to insert an
error post-processor.
What if, instead of SHE being a separate process that GHC ran (and is thus
not automatically cabal-installable and so on) on each source file, GHC
had a simple extensions interface, where an extension would be a module
that contained two functions and a type:
{{{
data State = ...
preprocess :: String -> (String, State)
postprocess :: String -> State -> String
}}}
GHC would take care of running the preprocessor before doing its own
thing, and would preserve the State and pass it back to postprocess the
error messages.
This would allow me to write something like {-# EXTENSION Extension.SHE
#-} and have it magically produce readable error messages (assuming
someone wrote an error postprocessor for SHE).
Of course, since the error messages don't really have a structured format,
there'd be no way for these things to compose, since a postprocessor could
only make assumptions about error messages it already knows (and not those
generated by other postprocessors). But this seems like a fairly low-
resistance way to test new features and have them actually be usable
without having to know the internals of the desugaring in the
preprocessor.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4886>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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