#2428: bad error message for multiple modules in the same file
-----------------------------+----------------------------------------------
Reporter: Isaac Dupree | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.8.2 | Severity: normal
Keywords: | Testcase:
Architecture: Unknown | Os: Unknown
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consider this file:
{{{
module MyMod where
foo :: Int
foo = 3
module Main (main) where
import MyMod (foo)
main :: IO ()
main = print foo
}}}
The layout rule dictates that this parses properly (the first module
clause ends when the second "module" gives a parse error, just like "in"
ends a "let"); this gets the same error:
{{{
module MyMod where
{ foo :: Int; foo = 3 }
module Main (main) where
{ import MyMod (foo); main :: IO (); main = print foo }
}}}
The Haskell98 report doesn't say anything about how modules are expected
to be laid out in files, so I had assumed it would work. The error is
{{{
parse error on input `module'
}}}
(except if Main comes before `MyMod`, ''and'' --make is used with ghc, we
get
{{{
Could not find module `MyMod':
Use -v to see a list of the files searched for.
}}}
even though `MyMod` is clearly (to a human) in that very file.)
It took me a long time to figure out what was wrong and what I had to do.
Admittedly I'm only slightly interested in GHC implementing support to
allow this, since if multiple files are involved at all it causes module-
finding trouble (obviously to me now); mostly I just want a good error
message, maybe something like "Each file must contain exactly one module.
Any module intended to be imported must be in an appropriately named file,
e.g. module `Module.Name' goes in `Module/Name.hs'."
( This happened to me a long time ago... but I was reminded by #2427 )
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2428>
GHC <http://www.haskell.org/ghc/>
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