使用runhaskell时出现“无法加载模块'Control.Monad.State'它是隐藏包'mtl-2.2.2'的成员”错误

Question

I tried running runhaskell InterpretSpec.hs , which then pulls from Interpret.hs this:

-- Look at how testing is set up in FORTH project and emulate here
-- Make sure you unit test every function you write
import Test.Hspec
import Test.QuickCheck
import Control.Exception (evaluate)
import Pascal.Data
import Pascal.Interpret
import Control.Monad.State
import Data.Map (Map)
import qualified Data.Map as Map
main :: IO ()
main = hspec $ do
  let startscope=SymbolTable{variables=Map.empty, global=Map.empty, loop=["notrunning"], functions=Map.empty, procedures=Map.empty, returnstring="", inmain=True}
  describe "eval" $ do
    it "takes the square root" $ do
        evalState (eval(Op1 "sqrt" (Real1 25.0))) startscope `shouldBe` (5.0)
    it "takes the cos" $ do
        evalState (eval(Op1 "cos" (Real1 0.0))) startscope `shouldBe` (1.0)
    it "takes the sin" $ do
        evalState (eval(Op1 "sin" (Real1 0.0))) startscope `shouldBe` (0.0)
    it "takes the sin" $ do
        evalState (eval(Op1 "sin" (Real1 0.0))) startscope `shouldBe` (0.0)
    it "takes the sin" $ do
        evalState (eval(Op1 "sin" (Real1 0.0))) startscope `shouldBe` (0.0)

mtl is included in the .cabal file, and I've referenced the suggested solutions at:

• Could not find module `Control.Monad.State` after updating mtl

and

• Could not find module 'Control.Monad.State' even though mtl is installed

and neither solves the issue.

Answer 1

On its own, runhaskell doesn't account for your cabal environment. You have to use it through cabal exec :

cabal exec runhaskell InterpretSpec.hs