foldm

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trait FoldM [T, M[_], U] extends AnyRef
A FoldM is a "left fold" over a data structure with:
A FoldM is a "left fold" over a data structure with:
- a 'start' value
- a 'fold' method to accumulate state
- an 'end' method to finalize the result
Both 'start' and 'end' have an effect which allows the whole folding to take place inside a context M.
If 'M' has an 'Apply' instance then FoldM can be made Applicative to allow the folding of two values U and S at the same time.
If 'M' has a 'Monad' instance then FoldM can be made into a 'Compose' instance which allows to compose 2 folds into one, for example:
- 'sum' computes the sum of some elements
- 'list' accumulates all the elements in a list
- the 'sum compose list' will accumulate the list of all the sums over some elements (this is a 'scan')
A FoldM can be used with a 'FoldableM' which produces the elements to fold over. Examples of FoldableM include
- a List
- an Iterator
- a scalaz Process
Usage example:
sum.run(List(1, 2, 3)) == 6
trait FoldableM [F[_], M[_]] extends AnyRef
A structure delivering elements of type A (variable type, like a List) and which can be folded over
trait FoldableMS [A, F, M[_]] extends AnyRef
A structure delivering elements of type A (fixed type, like an InputStream) and which can be folded over

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