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]


Without changing the code too drastically I see two immediate improvements, for one you can pull out the Leftconstructor 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
  if not $ isSameSize sa sb then
    InvalidVectorSize ay by

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 Tuples 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
        dot' a b = _dot (join a) (join b)
        areSimilarVectors = areVectors && areSameSize
        areVectors = ax == 1 && bx == 1
        areSameSize = ay == by
        failed =
          if not areVectors then
            if not areSameSize then
              InvalidVectorSize ay by

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
import Control.Monad.Except

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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