Build Error: Missing Imports for `msum` and `liftM` in StateFold.hs with GHC 9.6.7

[Cesartwothousands]

Build Error: Missing Imports for msum and liftM in StateFold.hs with GHC 9.6.7

Description

When building feynopt with GHC 9.6.7, the build fails with compilation errors in src/Feynman/Optimization/StateFold.hs. The errors indicate that msum and liftM are not in scope, even though they are used in the code. This appears to be a compatibility issue with newer GHC versions where these functions are no longer automatically exported from Control.Monad.State.Strict.

Error Messages

src/Feynman/Optimization/StateFold.hs:200:26: error: [GHC-88464]
    Variable not in scope:
      msum
        :: [Maybe
              (Var, Var,
               Multilinear Var FF2 Feynman.Algebra.Polynomial.Multilinear.Mult)]
           -> Maybe (Var, Var, SBool Var)
    Suggested fix:
      Perhaps use one of these:
        'sum' (imported from Data.List),
        'U.sum' (imported from Feynman.Util.Unicode)
    |
200 | matchHH pp cand cutoff = msum . map go $ Set.toAscList cand where
    |                          ^^^^

src/Feynman/Optimization/StateFold.hs:211:22: error: [GHC-88464]
    Variable not in scope:
      msum :: [Maybe (Var, SBool Var)] -> Maybe (Var, SBool Var)
    |
211 | matchOmega pp cand = msum . map go $ Set.toAscList cand where
    |                      ^^^^

src/Feynman/Optimization/StateFold.hs:289:13: error: [GHC-88464]
    Variable not in scope:
      liftM
    |
289 |     v'   <- liftM ofVar $ allocTemp
    |             ^^^^^

src/Feynman/Optimization/StateFold.hs:456:19: error: [GHC-88464]
    Variable not in scope:
      liftM
    |
456 |   WSeq _ xs    -> liftM concat $ mapM (applyStmt d) xs
    |                   ^^^^^

Environment

• GHC Version: 9.6.7 (installed via GHCup)
• Cabal Version: 3.14.2.0 (installed via GHCup)
• OS: Linux (Ubuntu 22.04, kernel 6.8.0-64-generic)
• Architecture: x86_64

Workaround

Add an explicit import in src/Feynman/Optimization/StateFold.hs:

import Control.Monad (msum, liftM)