Cabal related exception when calling System.Eval.Haskell.eval

[adam.a...@gmail.com]

Hi,

When I try to use eval from System.Eval.Haskell in plugins-1.5.5.0 I get 

*** Exception: user error (Use of GHC's environment variable GHC_PACKAGE_PATH is incompatible with Cabal. Use the flag --package-db to specify a package database (it can be used multiple times).)

From trying to do this:

$ stack ghci

Using main module: Package `plop' component exe:plop-exe with main-is file: /Users/adam/plop/app/Main.hs

The following GHC options are incompatible with GHCi and have not been passed to it: -threaded

Configuring GHCi with the following packages: plop

GHCi, version 7.10.2: http://www.haskell.org/ghc/  :? for help

[1 of 2] Compiling Lib              ( /Users/adam/plop/src/Lib.hs, interpreted )

[2 of 2] Compiling Main             ( /Users/adam/plop/app/Main.hs, interpreted )

Ok, modules loaded: Lib, Main.

syntax:  :module [+/-] [*]M1 ... [*]Mn

*Main> import System.Eval.Haskell

*Main System.Eval.Haskell> eval "plop" []

*** Exception: user error (Use of GHC's environment variable GHC_PACKAGE_PATH is incompatible with Cabal. Use the flag --package-db to specify a package database (it can be used multiple times).)

*Main System.Eval.Haskell>

As I've just started trying out stack, and never grokked cabal, I'm not at all sure how to go about getting this to work.  Any advice would thus be welcome.

Thanks,

Adam

[Neil Mitchell]

Hi Adam,

Alas, Cabal chokes on that environment variable, and stack sets it. I worked around this in the Shake test suite with the code at https://github.com/ndmitchell/shake/blob/master/src/Test/Docs.hs#L24

Basically, take GHC_PACAKGE_PATH and massage it to be a Cabal flag. I still don't understand why Cabal requires me to move the variable, when it could do it itself...

Thanks, Neil 

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