On Sun, Feb 1, 2015 at 4:42 PM, S. Doaitse Swierstra <doaitse@swierstra.net> wrote:

With the new version of GHC (7.8.3) I am running into problems with cpp.

The header of one of the files of my uu-parsinglib library reads as follows:

{-# LANGUAGE NoMonomorphismRestriction,
RankNTypes,
FlexibleContexts,
CPP #-}
#define DEMO(p,i) demo "p" i p
#define DEMOG(p,i) demo "p" i (mkP (p))
module Text.ParserCombinators.UU.Demo.MergeAndPermute where

...

However when I try to compile this file I get error messages like:

Text/ParserCombinators/UU/Demo/Demo.hs:88:17:
Not in scope: data constructor ‘DEMOG’

(1) ghc is at 7.8.4. I *think* 7.8.4 does slightly better here, but only slightly:

(2) May I guess that Demo.hs line 88 starts with an identifier with a prime in it? GHC 7.8.3 on OS X tries to make clang's cpp behave like gcc's, but does not completely succeed; clang's cpp will ignore macros in what it thinks are quoted strings/chars, so fails when faced with things like

foo' = ... something using a cpp macro here ...

One workaround is to install ghc from MacPorts (forces gcc's cpp) or the github ghcformacosx repo (which I think is Homebrew-based? so it depends on how much you like code with no error checking to speak of and curl-pipe-sh "hack me please" installation).

7.8.4 may also provide some way to point cpp to "gcc --traditional -E". Long term, we need to move away from using a C preprocessor for Haskell code; there are no guarantees that it won't try to enforce C syntax on you, like clang's does.

--

brandon s allbery kf8nh sine nomine associates

allbery.b@gmail.com ballbery@sinenomine.net

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