Resolving readEither on ADT

Question

Hello i was wondering if given an Algebraic Data Type how can i resolve the following problem :

u::Text->String
u =Data.Text.unpack

 data Numeric=I Int | D Double

 readNumeric::Text->Either String Numeric
 readNumeric text=let str=u text in
                      if '.' `elem` str then 
                       D (readEither str::Either String Double)
                      else
                       I (readEither str::Either String Int)

How can i cover both sides of Either given an ADT? Practically 2*2 cases , uniformly?

I was considering using fromRight on each branch ( e.g fromRight (D 0) ) of the pattern-matching (in our case if since there are only 2 cases) but i do not know if it is the best approach . But fromRight returns the inner type..i want to preserve the Either

Any ideas?

Answer 1

Isn't this is what you need?

readNumeric::Text -> Either String Numeric
readNumeric text=let str = u text in
                      if '.' `elem` str then 
                       fmap D (readEither str::Either String Double)
                      else
                       fmap I (readEither str::Either String Int)