Supply a list of default values if list is empty in Haskell? -

i'm parsing command line arguments determine value want program return

but if supply no values, want add bunch of default values list.

kind of python's xs = parsed_list or [1,2,3]

using guards:

xs | null parsed_list = [1,2,3]    | otherwise        = parser_list

using if: (as @mephy suggested)

xs = if null parsed_list [1,2,3] else parsed_list

using pattern matching: (see @jtobin's answer)

using foldr (not recommended):

xs = foldr (\_ _ -> parsed_list) [1,2,3] parsed_list

using custom operator:

ifempty :: [a] -> [a] -> [a] ifempty [] def = def ifempty ys _   = ys  xs = parsed_list `ifempty` [1,2,3]

UV code