failing to parse a nested generator in the inner loop

[julochrobak]

The following expressions works fine:
[ {b, a} | b <- [0,1], a <- [2,3] ]

but this one fails with a compilation error:
[ {b, a} | b <- [0,1], a <- [ c | c <- [2,3]] ]

{"line":0,"column":0,"error":"unknown identifier 'c'"}

[julochrobak]

This is a problem with identifiers scope definition when parsing a comprehension. All identifiers are declared on a global scope and therefore there is a strict mode enabled after the first generator is parsed to enforce that every identifier must be first declared and than used. However, the second example shows that this causes an issue.

Also because of all the identifiers are declared within a global scope, the following comprehensions are valid and work, but don't make much sense:

$ bin/comp '[ b | b <- [ c | c <- [2,3]], c == 3 ]'
[ 2, 3 ]
$

$ bin/comp '[ b | b <- [ c | c <- [2,3], c == 2], b == c ]'
$