Example Problem:
From two lists L and M, create the list of all pairs :
first component from L,
second component from M
e.g.
L = [a,b,c,d]
M = [1,2,3]
result
[[a,1],[a,2],[a,3],[b,1],[b,2],[b,3],[c,1],[c,2],º,[d,3]]
"Cartesian product"
How to approach:
First do for a single element, say X, of L:
[[x,1], [x,2], [x,3]]
Use map :
map((Y) Þ [x,y], M)
›
X is "imported"; it is an otherwise unbound variable
Second, map a function which has X as its argument over each value of L:
This gives, for the current example,
[
[[a,1],[a,2],[a,3]], ¨ 1st inner map
[[b,1],[b,2],[b,3]], ¨ 2nd
[[c,1],[c,2],[c,3]],
[[d,1],[d,2],[d,3]]
]
The list above is not quite it; we want all lists to be appended together.
mappend((x)Þ map((Y)Þ [x,y],M),L)
Could define
pairs(L,M) = › ;
Note: This problem is homework-related.
