On Sun, Aug 9, 2015 at 10:23 PM, Richard Eisenberg
This can be done today:
allMinus m ns = [ n' | n <- ns, Just n' <- [n -? m] ]
The syntax is a bit regrettable, but it works quite well.
On a somewhat related note, this trick is a nice way to introduce let-like bindings in languages like Python that have comprehension syntax and no explicit support for pure intermediate bindings: [ str(x) + ' is ' + str(i) + ' dozens' for i in range(1, 9) for x in [12*i] ] It’s also useful when you want to simulate monadic-ish things sometimes: x = {'a': { 'b': 'c', 'd': 'e'}, 'f': 'g'} [ z for y in [x.get('a')] if y for z in [y.get('b')] if z ] # => ['c'] [ z for y in [x.get('q')] if y for z in [y.get('b')] if z ] # => [] Almost feels like having some simple monads!