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deque-blog/MoneyFowler4.hs

Created August 13, 2017 16:24
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MoneyFowler4.hs
add :: Money -> Money -> Maybe Money
add m1 m2 =
if currency m1 != currency m2 -- If the two currencies are different
then Nothing -- * Return an empty result
else Just $ Money { -- * Else return a new Money instance
amount = amount m1 + amount m2, -- which is the sum of the two inputs
currency = currency m1 }
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