[ebola1717]

I've written a fair share of Haskell, and I still get tripped up by list comprehensions in python - even my own. It's not that it's impossible to understand, and when there's only one predicate, I think it's fine:

  for row in [[i*j for i in range(1, 8)] for j in some_list if j % 2 == 0]:
    some_op(row)

vs

  for j in some_list:
    if j % 2 == 0:
      row = [ i * j for i in range(1,8) ]
      some_op(row)

I would compare it to sentences and paragraphs. The former feels like a run-on sentence, while the latter is more obvious, cause it has one predicate per line. Also, list comprehensions are a bit like yoda-speak - it introduces the verb before the subject. You have to untangle the order of operations, rather than having the order read top-down and left-right.

Of course, I'm a rubyist, so I'd prefer:

  some_list.select { |j|   j % 2 == 0 }
           .map    { |j|   (1..8).map { |i| i * j } }
           .map    { |row| some_op(row) }

Though definitely need to do something about that second line.

Haskell list comprehensions are a bit easier to parse because they have symbolic delimiters, the fact that Haskell is naturally more terse, and because you can always check the type of the list

  [ [i*j | i <-[1..8]] | j <- [1..4], j % 2 == 0 ]