Comprehensions

YASL supports list- and table-comprehensions, for creating a new list or table from an existing one. These can be used to replace both map and filter in a more functional style of programming. List- and table-comprehensions can iterate over anything a for-loop can.

List Comprehensions

The syntax for list comprehensions is:

"[" expr "for" id "<-" expr ("if" expr)? "]"

For example, the following would produce a new list from ls with every element doubled:

[ 2 * x for x <- ls ]

The following would make a new list with only the odd elements:

[ x for x <- ls if x % 2 != 0 ]

These two can also be combined. The following produces a new list containing the square of every odd element:

[ x * x for x <- ls if x % 2 != 0 ]

Table Comprehensions:

The syntax for table comprehensions is:

"{" expr ":" expr "for" id "<-" expr ("if" expr)? "}"

Table comprehensions can use the same mapping and filtering as a list comprehension.