Add some more augmented assignment operators.

hs/ImperativeProgramming.hs

@@ -29,8 +29,13 @@ instance Monad (Imperative a) where
    return x = Imperative $ \env -> (env, x)
name .= value = Imperative $ \env -> (M.insert name value env, value)
entedAssignment op = \name .+= value = Imperative $ \env ->
    (M.insertWith (+) name value env, value + (fromJust $M.lookup name env))
augmentedAssignment op = \entedAssignment op = \name value -> Imperative $ \env ->
    (M.insertWith (flip op) name value env, (fromJust $ M.lookup name env) `op` value)
(.+=) = augmentedAssignment (+)
(.-=) = augmentedAssignment (-)
(.*=) = augmentedAssignment (*)
(./=) = augmentedAssignment (/)
binaryOp op = \var1 var2 -> Imperative $ \env ->
    (env, fromJust $ op <$> M.lookup var1 env <*> M.lookup var2 env)