I have a Haskell source file which using Unicode syntax:
{-# LANGUAGE UnicodeSyntax #-}
succ' :: Int → Int
succ' = succ
main :: IO ()
main = print $ succ' 1
This parses and runs fine with GHC. Additionally, stylish-haskell and hlint (both based on haskell-src-exts) can read this file without any trouble. However, when I try to parse it myself using haskell-src-exts:
import Language.Haskell.Exts (parseModule)
main = do
x <- readFile "test.hs"
print $ parseModule x
I get the error message:
ParseFailed (SrcLoc {srcFilename = "<unknown>.hs", srcLine = 6, srcColumn = 1}) "TypeOperators is not enabled"
However, providing UnicodeSyntax explicitly in the extensions list or using parseFile works just fine:
import Language.Haskell.Exts
main = do
x <- readFile "test.hs"
print $ parseModuleWithMode defaultParseMode
{ extensions = [UnicodeSyntax]
} x
parseFile "test.hs" >>= print
Any idea why the first approach fails?
From a cursory glance at the source, it doesn't look like parseModule
extracts language pragmas from the source before parsing (parseFile
does do that by calling getExtensions
). By the time parsing has begun, it is already too late to enable unicode syntax.
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