3. List Comprehensions
3 List Comprehensions
3.1 Simple Examples
This section starts with a simple example, showing a generator and a filter:
> [X || X <- [1,2,a,3,4,b,5,6], X > 3]. [a,4,b,5,6]
This is read as follows: The list of X such that X is taken from the list [1,2,a,...] and X is greater than 3.
The notation X <- [1,2,a,...] is a generator and the expression X > 3 is a filter.
An additional filter, integer(X), can be added to restrict the result to integers:
> [X || X <- [1,2,a,3,4,b,5,6], integer(X), X > 3]. [4,5,6]
Generators can be combined. For example, the Cartesian product of two lists can be written as follows:
> [{X, Y} || X <- [1,2,3], Y <- [a,b]].
[{1,a},{1,b},{2,a},{2,b},{3,a},{
