80 lines
2.0 KiB
Python
80 lines
2.0 KiB
Python
'''Flatten a nested list'''
|
|
|
|
from itertools import (chain)
|
|
|
|
|
|
# ----------------------- FLATTEN ------------------------
|
|
|
|
# flatten :: NestedList a -> [a]
|
|
def flatten(x):
|
|
'''A list of atomic values resulting from fully
|
|
flattening an arbitrarily nested list.
|
|
'''
|
|
return concatMap(flatten)(x) if (
|
|
isinstance(x, list)
|
|
) else [x]
|
|
|
|
|
|
# ------------------------- TEST -------------------------
|
|
def main():
|
|
'''Test: flatten an arbitrarily nested list.
|
|
'''
|
|
print(
|
|
fTable(__doc__ + ':')(showList)(showList)(
|
|
flatten
|
|
)([
|
|
[[[]]],
|
|
[[1, 2, 3]],
|
|
[[1], [[2]], [[[3, 4]]]],
|
|
[[1], 2, [[3, 4], 5], [[[]]], [[[6]]], 7, 8, []]
|
|
])
|
|
)
|
|
|
|
|
|
# ----------------------- GENERIC ------------------------
|
|
|
|
# compose (<<<) :: (b -> c) -> (a -> b) -> a -> c
|
|
def compose(g):
|
|
'''Right to left function composition.'''
|
|
return lambda f: lambda x: g(f(x))
|
|
|
|
|
|
# concatMap :: (a -> [b]) -> [a] -> [b]
|
|
def concatMap(f):
|
|
'''A concatenated list over which a function has been mapped.
|
|
The list monad can be derived by using a function f which
|
|
wraps its output in a list,
|
|
(using an empty list to represent computational failure).
|
|
'''
|
|
def go(xs):
|
|
return chain.from_iterable(map(f, xs))
|
|
return go
|
|
|
|
|
|
# fTable :: String -> (a -> String) ->
|
|
# (b -> String) ->
|
|
# (a -> b) -> [a] -> String
|
|
def fTable(s):
|
|
'''Heading -> x display function ->
|
|
fx display function ->
|
|
f -> value list -> tabular string.'''
|
|
def go(xShow, fxShow, f, xs):
|
|
w = max(map(compose(len)(xShow), xs))
|
|
return s + '\n' + '\n'.join([
|
|
xShow(x).rjust(w, ' ') + (' -> ') + fxShow(f(x))
|
|
for x in xs
|
|
])
|
|
return lambda xShow: lambda fxShow: lambda f: lambda xs: go(
|
|
xShow, fxShow, f, xs
|
|
)
|
|
|
|
|
|
# showList :: [a] -> String
|
|
def showList(xs):
|
|
'''Stringification of a list.'''
|
|
return '[' + ','.join(str(x) for x in xs) + ']'
|
|
|
|
|
|
if __name__ == '__main__':
|
|
main()
|