'stack ghc' doesn't run C preprocessor?

[mitchellwrosen]

Sorry, hit submit on accident... filling out details now

[mitchellwrosen]

I was trying to verify a bug in the latest mwc-random:

> stack unpack mwc-random-0.13.4.0
> cd mwc-random-0.13.4.0

Give it a stack.yaml...

> cat <<EOF >stack.yaml
resolver: lts-5.5
EOF

Make a file to compile...

> cat <<EOF >foo.hs
import System.Random.MWC
main = pure ()
EOF

Compile it

> stack ghc foo.hs

System/Random/MWC.hs:103:0:
     error: missing binary operator before token "("
     #if MIN_VERSION_primitive(0,6,0)
     ^

System/Random/MWC.hs:115:0:
     error: missing binary operator before token "("
     #if !MIN_VERSION_base(4,8,0)
     ^

System/Random/MWC.hs:482:0:
     error: missing binary operator before token "("
     #if MIN_VERSION_primitive(0,6,0)

It seems to work fine with mwc-random-0.13.4.0 in the snapshot database, rather than the local database.

This is stack ver 1.0.4

[mgsloan]

stack ghc is pretty much just an alias for stack exec ghc, with a bit of extra smarts to handle the --package flag. In other words, it does not use any cabal information at all, but will use the right GHC and package databases.

There's a PR in limbo state that tries adding something like this, see the discussion here - #1737 .

Anyway, the main problem is probably that your "foo.hs" is at the root dir of mwc-random and uses modules from it, and it lacks a src dir. This means that ghc will find these modules and try to compile them. Instead, put foo.hs in a subfolder. Then, you can do stack ghc foo.hs --package mwc-random (the --package part is only necessary if you don't want to first do a stack build)