hpp is a Haskell pre-processor that is also a C90-compatible
pre-processor (with the addition of a --cpp flag). It is
packaged as both a library and an executable.
To use as a Haskell preprocessor for resolving #ifdef conditionals
and macro expansion, an invocation might look like,
hpp -DDEBUG Foo.hs
To use as a C preprocessor, an invocation might look like,
hpp -DDEBUG --cpp foo.c
To have GHC use hpp as the C pre-processor, add this line to the top
of a Haskell source file that makes use of the CPP LANGUAGE
pragma,
{-# OPTIONS_GHC -cpp -pgmPhpp #-}
Or add this line to your .cabal file:
ghc-options: -pgmPhpp
Note that you will need to ensure that the hpp executable is available in your build environment (e.g. you can add hpp as a build-depends in your .cabal file).
The hpp executable is a command-line interface to the hpp library. While the hpp package has been designed to have minimal dependencies beyond what the GHC compiler itself uses, it does include a few small, framework-free unit tests that demonstrate basic usage as a library. In the testIf example, we preprocess the sourceIfdef input with a starting definition equivalent to #define FOO 1. In testArith1, we exercise basic integer arithmetic and comparison. The hppHelper function shows how to run your source input through the preprocessor: expand initialState (preproces mySource). If you want to support #includeing other files, you will use runHpp or streamHpp that operate in IO and support searching among a list of include paths.
{-# LANGUAGE OverloadedStrings #-}
import Control.Monad.Trans.Except
import Data.ByteString.Char8 (ByteString)
import Data.Maybe (fromMaybe)
import Data.Monoid ((<>))
import Hpp
import System.Exit
sourceIfdef :: [ByteString]
sourceIfdef = [ "#ifdef FOO"
, "x = 42"
, "#else"
, "x = 99"
, "#endif" ]
sourceArith1 :: ByteString -> [ByteString]
sourceArith1 s = [ "#define x 3"
, "#if 5 + x > " <> s
, "yay"
, "#else"
, "boo"
, "#endif" ]
hppHelper :: HppState -> [ByteString] -> [ByteString] -> IO Bool
hppHelper st src expected =
case runExcept (expand st (preprocess src)) of
Left e -> putStrLn ("Error running hpp: " ++ show e) >> return False
Right (res, _) -> if hppOutput res == expected
then return True
else do putStr ("Expected "++show expected++", got")
print (hppOutput res)
return False
testElse :: IO Bool
testElse = hppHelper emptyHppState sourceIfdef ["x = 99\n","\n"]
testIf :: IO Bool
testIf = hppHelper (fromMaybe (error "Preprocessor definition did not parse")
(addDefinition "FOO" "1" emptyHppState))
sourceIfdef
["x = 42\n","\n"]
testArith1 :: IO Bool
testArith1 = (&&) <$> hppHelper emptyHppState (sourceArith1 "7") ["yay\n","\n"]
<*> hppHelper emptyHppState (sourceArith1 "8") ["boo\n","\n"]
main :: IO ()
main = do results <- sequenceA [testElse, testIf, testArith1]
if and results then exitWith ExitSuccess else exitWith (ExitFailure 1)
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