foldm

Type Members

1. 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

2. trait FoldableM[F[_], M[_]] extends AnyRef

   

   A structure delivering elements of type A (variable type, like a List) and which can be folded over

3. 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