lookupM :: Name -> Environment -> M Value
lookupM x env = case lookup x env of
  Just v  -> return v
  Nothing -> return Wrong
lookupM :: Name -> Environment -> M Value
lookupM x env = case lookup x env of
  Just v  -> return v
  Nothing -> return Wrong
lookupM x env = case lookup x env of
  Just v  -> return v
  Nothing -> return Wrong