Home » Refactor code to be more succinct but yet preserve the distinction of the `if` [closed]

# Refactor code to be more succinct but yet preserve the distinction of the `if` [closed]

## Solutons:

Without changing the code too drastically I see two immediate improvements, for one you can pull out the `Left`constructor in front of the call to fail, thus keeping `Right` and `Left` on the same level and making the distinction clearer:

``````if areSimilarVectors sa sb
then Right \$ dot' a b
else Left \$ failed sa sb
``````

Secondly because the code handles failure cases I’d suggest you reverse the predicates for the ifs to reduce the distance between Reason <-> Error

``````if not \$ isVector sa sb then
VectorsExpected
else
if not \$ isSameSize sa sb then
InvalidVectorSize ay by
else
UnexpectedError
``````

Other things you might want to consider is the naming of `isVector` and the amount of shadowing of `sa` and `sb`. Why are you using a where clause and then still pass the arguments around explicitly? Maybe it would be even better if you matched the `Tuple`s in the toplevel pattern match and stopped using `fst` and `snd` alltogether? Applying that we get to:

``````dot :: Matrix -> Matrix -> Either MatrixError Number
dot (Matrix a (Tuple ax ay)) (Matrix b (Tuple bx by)) =
if areSimilarVectors then Right \$ dot' a b else Left failed
where
dot' a b = _dot (join a) (join b)
areSimilarVectors = areVectors && areSameSize
areVectors = ax == 1 && bx == 1
areSameSize = ay == by
failed =
if not areVectors then
VectorsExpected
else
if not areSameSize then
InvalidVectorSize ay by
else
UnexpectedError
``````

I would also look at using guards:

``````dotProduct :: Num a => [a] -> [a] -> Either String a
dotProduct as bs
| notSimilar = Left "bad operands"
| otherwise  = Right \$ sum \$ zipWith (*) as bs
where notSimilar = length as /= length bs
``````

Another option is to use `throwError`:

``````import Control.Monad

dotProduct'' :: Num a => [a] -> [a] -> Either String a
dotProduct'' as bs = do
when (length as /= length bs) \$ throwError "bad operands"
return \$ sum \$ zipWith (*) as bs
``````

You’re forcing the reader to read the code linearly, but it also removes a level of indentation.

The Either monad allows you to use do notation here:

``````dot :: Matrix -> Matrix -> Either MatrixError Number
dot (Matrix a (Tuple ax ay)) (Matrix b (Tuple bx by)) = do
unless (ax == 1 && bx == 1) \$ Left VectorsExpected
unless (ay == by) \$ Left \$ InvalidVectorSize ay by
Right \$ _dot (join a) (join b)
``````

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