scan

This page is a reference guide for the scan family of operators. It describes:

• The behaviour of scan, scan1, scanMap and scanMonoid.

• How scan operators propagate chunks.

As the scan family of operators have normal error propagation and finalizer handling, these are not described.

Behaviour

The scan family of operators perform a left fold over an input stream and output intermediate results.

scan

The scan operator pulls an element from its input stream, evaluates a function with its previous result, then outputs the result. It is analogous to scan on lists.

The following example scans over an input stream of characters to produce a string. A character ch is pulled and combined with an accumulated string str with the s"$str-$ch" function.

scan1

The scan1 operator is similar to scan, but uses the first element pulled from the input stream to evaluate the result.

scanMonoid

The scanMonoid operator scans over its input with a Monoid typeclass instance.

The following example uses the String monoid instance. The empty element of the instance "" is outputted first. The combine function of the instance concatenates two strings.

scanMap

The scanMap operator maps over its input then scans with a Monoid typeclass instance. input.scanMap(f) is equivalent to input.map(f).scanMonoid.

Chunk propagation

scan

The scan operator preserves the chunks of its input. The first argument to scan is outputted as a singleton chunk.

scan1

scan1 preserves the chunks of its input, with the exception of the first chunk. The first element of the first chunk is outputted as a singleton chunk.