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Module: Maybe
Function: catMaybes
Type: [Maybe a] -> [a]
Description: creates a list of Just values from a Maybe list
Related:

Example 1
Program source: 

a = [(1,'A'),(2,'B'),(3,'C')]

Input: catMaybes [lookup 0 a, lookup 1 a, lookup 3 a, lookup 12 a]

Output: "AC"

Example 2
Program source: 

b = [(1,11),(2,22),(3,33)]

Input: catMaybes [lookup 0 b, lookup 1 b, lookup 3 b, lookup 12 b]

Output: [11,33]