CODEWITHSUNDEEP
haskell
softshipper
softshipper

Reputation: 34099

Monoid of larger type

I am trying to learn haskell and reading the haskellbook.

In the book, the author mentioned larger type as follow: 

instance Monoid b => Monoid (a -> b)
instance (Monoid a, Monoid b) => Monoid (a, b)
instance (Monoid a, Monoid b, Monoid c) => Monoid (a, b, c)

What these Monoids have in common is that they are giving you a new Monoid for a larger type by reusing the Monoid instances of types that represent components of the larger type.

What does he mean with larger datatype?

Upvotes: 1

Views: 88

Answers (1)

Anton Xue
Anton Xue

Reputation: 833

I think the author means this: a tuple may contain some Monoid instance a, b, and c. However, we can view the Monoid instances in those tuples collectively, and thus define a new Monoid of type (a, b, c). Thus, from 3 smaller Monoid instances grouped together in a tuple give rise to a "larger" Monoid instance over (a, b, c).

Upvotes: 5

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