Examples

res = {};

for each a in x do

?{ (a,b) | a ? x, b ? y } for each b in y do

res = res ? {(a,b)};

return res;

?{ (a,b) | a ? [1,2,3], b ? {4,5} }

= { (1,4), (1,5), (2,4), (2,5), (3,4), (3,5) }

+{ a | a ? [1,2,3], a ? 2 }

= 2+3 = 5

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This is an example of a comprehension that contains two generators but no filter. It performs the following computation: for each element a of x and for each element b of y, insert the pair (a,b) to the resulting set, which is initially empty. For example, if x is the list [1,2,3] and y is the bag {4,5}, the result is a set with 6 pairs. Another example is the above comprehension that filters out of the list [1,2,3] all the elements a less than 2 and adds together the rest.