def make_instance(typeclass, cls, bind):
from hask3.hack import is_builtin
from hask3.lang.type_system import build_instance
from hask3.lang.syntax import H, t
bind = bind ** (H[Monad, "m"]/
t("m", "a") >> (H/ "a" >> t("m", "b")) >> t("m", "b"))
if not is_builtin(cls):
def bind_wrap(s, o):
return Monad[s].bind(s, o)
cls.__rshift__ = bind_wrap
build_instance(Monad, cls, {"bind": bind})
def test_typeclasses_x(self):
# Instantiate using defined higher-kinded type
instance(Composite, t(t(Tree, 'a'), Maybe, [t(Tree, 'a')])).where(
children=tree_children
)
# String representation for higher-kinded type.
self.assertEqual(str(t(t(Tree, 'a'), Maybe, [t(Tree, 'a')])),
'((Tree a) Maybe [(Tree a)])')
def in_either(fn):
"""Decorator for monadic error handling.
If the decorated function raises an exception, return the exception inside
`Left`. Otherwise, take the result and wrap it in `Right`.
"""
from hask3.lang.syntax import typify, t
def closure_in_either(*args, **kwargs):
try:
return Right(fn(*args, **kwargs))
except Exception as e:
return Left(e)
return typify(fn, hkt=lambda x: t(Either, "aa", x))(closure_in_either)
def in_maybe(fn):
"""Decorator for monadic error handling.
If the decorated function raises an exception, return `Nothing`.
Otherwise, take the result and wrap it in a `Just`.
"""
from hask3.lang.syntax import typify, t
def closure_in_maybe(*args, **kwargs):
try:
return Just(fn(*args, **kwargs))
except: # noqa
return Nothing
return typify(fn, hkt=lambda x: t(Maybe, x))(closure_in_maybe)
"""
@classmethod
def make_instance(typeclass, cls, bind):
from hask3.hack import is_builtin
from hask3.lang.type_system import build_instance
from hask3.lang.syntax import H, t
bind = bind ** (H[Monad, "m"]/
t("m", "a") >> (H/ "a" >> t("m", "b")) >> t("m", "b"))
if not is_builtin(cls):
def bind_wrap(s, o):
return Monad[s].bind(s, o)
cls.__rshift__ = bind_wrap
build_instance(Monad, cls, {"bind": bind})
@sig(H[Monad, "m"]/ t("m", "a") >> (H/ "a" >> t("m", "b")) >> t("m", "b"))
def bind(m, fn):
"""``bind :: Monad m => m a -> (a -> m b) -> m b``
Monadic bind.
"""
return Monad[m].bind(m, fn)
@sig(H[Monad, "m"]/ t("m", t("m", "a")) >> t("m", "a"))
def join(m):
"""``join :: Monad m => m (m a) -> m a``
The join function is the conventional monad join operator. It is used to
remove one level of monadic structure, projecting its bound argument into
p = (lambda x: DL.product(toList(x))) if product is None else product
attrs = {"foldr": foldr, "foldr1": foldr1, "foldl": foldl,
"foldl_": foldl_, "foldl1": foldl1, "toList": toList,
"null": null, "length": length, "elem": elem, "maximum": ma,
"minimum": mi, "sum": sum, "product": p}
build_instance(Foldable, cls, attrs)
if not hasattr(cls, "__len__") and not is_builtin(cls):
cls.__len__ = length
if not hasattr(cls, "__iter__") and not is_builtin(cls):
cls.__iter__ = lambda x: iter(toList(x))
@sig(H[(Foldable, "t")]/ (H/ "a" >> "b" >> "b") >> "b" >> t("t", "a") >> "b")
def foldr(f, z, t):
"""``foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b``
Right-associative fold of a structure.
"""
return Foldable[t].foldr(f, z, t)
@sig(H[(Foldable, "t")]/ (H/ "a" >> "a" >> "a") >> t("t", "a") >> "a")
def foldr1(f, t):
"""``foldr1 :: Foldable t => (a -> a -> a) -> t a -> a``
A variant of foldr that has no base case, and thus may only be applied to
non-empty structures.
Minimal complete definition:
- ``traverse``
"""
@classmethod
def make_instance(typeclass, cls, traverse, sequenceA=None, mapM=None,
sequence=None):
from hask3.lang.type_system import build_instance
attrs = {"traverse": traverse, "sequenceA": sequenceA, "mapM": mapM,
"sequence": sequence}
build_instance(Traversable, cls, attrs)
@sig(H[(Applicative, "f"), (Traversable, "t")]/
(H/ "a" >> t("f", "b")) >> t("t", "a") >> t("f", t("t", "b")))
def traverse(f, t):
"""``traverse :: (Traversable t, Applicative f) => (a -> f b) -> t a -> f (t b)``
Map each element of a structure to an action, evaluate these these actions
from left to right, and collect the results. For a version that ignores
the results see `traverse_`:func:.
"""
return Traversable[t].traverse(f, t)
@sig(H[(Applicative, "f"), (Traversable, "t")]/
t("t", t("f", "a")) >> t("f", t("t", "a")))
def sequenceA(t):
"""``sequenceA :: (Traversable t, Applicative f) => t (f a) -> f (t a)``
If the decorated function raises an exception, return the exception inside
`Left`. Otherwise, take the result and wrap it in `Right`.
"""
from hask3.lang.syntax import typify, t
def closure_in_either(*args, **kwargs):
try:
return Right(fn(*args, **kwargs))
except Exception as e:
return Left(e)
return typify(fn, hkt=lambda x: t(Either, "aa", x))(closure_in_either)
@sig(H / (H / "a" >> "c") >> (H / "b" >> "c") >> t(Either, "a", "b") >> "c")
def either(fa, fb, e):
"""``either :: (a -> c) -> (b -> c) -> Either a b -> c``
Case analysis for the Either type. If the value is Left(a), apply the
first function to a; if it is Right(b), apply the second function to b.
"""
from hask3.lang.syntax import caseof, m, p
return ~(caseof(e) | m(Left(m.a)) >> fa(p.a) | m(Right(m.b)) >> fb(p.b))
@sig(H / [t(Either, "a", "b")] >> ["a"])
def lefts(xs):
"""``lefts :: [Either a b] -> [a]``
def make_instance(cls, instance, children):
children = children ** (H/ 'a' >> t('f', 'b'))
build_instance(cls, instance,
{'children': lambda self: children(self)})
container of type `f`.
Attributes:
- ``children :: a -> f b``
'''
@classmethod
def make_instance(cls, instance, children):
children = children ** (H/ 'a' >> t('f', 'b'))
build_instance(cls, instance,
{'children': lambda self: children(self)})
Tree, Leaf, Node = data.Tree('a') == (
d.Leaf | d.Node('a', [t(data.Tree, 'a')]) &
deriving(Show, Eq)
)
def tree_children(t):
return ~(caseof(t)
| m(Leaf) >> Nothing
| m(Node(m.p, m.xs)) >> Just(p.xs))
class TestTypeclassX(unittest.TestCase):
def test_typeclasses_x(self):
# Instantiate using defined higher-kinded type
instance(Composite, t(t(Tree, 'a'), Maybe, [t(Tree, 'a')])).where(
children=tree_children
from hask3.lang.syntax import t
# Current implementation is just a wrapper around Python's Fraction. This is
# not a long-term solution (not extensible beyond builtin types) but it will
# do for now.
from hask3.Data.Num import Ratio
from hask3.Data.Num import R # noqa
from hask3.Data.Num import toRational # noqa
from hask3.Data.Num import Integral
from hask3.Data.Num import RealFrac
from hask3.Data.Num import Rational
@sig(H[(Integral, "a")] / t(Ratio, "a") >> "a")
def numerator(ratio):
"""``numerator :: Integral a => Ratio a -> a``
Extract the numerator of the ratio in reduced form: the numerator and
denominator have no common factor and the denominator is positive.
"""
from hask3.Data.Num import toRatio
return toRatio(ratio[0], ratio[1])[0]
@sig(H[(Integral, "a")] / t(Ratio, "a") >> "a")
def denominator(ratio):
"""``denominator :: Integral a => Ratio a -> a``
If the decorated function raises an exception, return `Nothing`.
Otherwise, take the result and wrap it in a `Just`.
"""
from hask3.lang.syntax import typify, t
def closure_in_maybe(*args, **kwargs):
try:
return Just(fn(*args, **kwargs))
except: # noqa
return Nothing
return typify(fn, hkt=lambda x: t(Maybe, x))(closure_in_maybe)
@sig(H / "b" >> (H / "a" >> "b") >> t(Maybe, "a") >> "b")
def maybe(default, f, maybe_a):
"""Apply `f` to `maybe_a` (if possible) or return `default`.
Take a `default` value, a function, and a Maybe value. If the Maybe value
is Nothing, return the default value. Otherwise, apply the function to
the value inside the Just and return the result.
Type signature: ``maybe :: b -> (a -> b) -> Maybe a -> b``.
"""
return default if maybe_a == Nothing else f(maybe_a[0])
@sig(H / t(Maybe, "a") >> bool)
def isJust(a):
- ``fromRational``
- ``div``
"""
@classmethod
def make_instance(typeclass, cls, fromRational, div, recip=None):
from hask3.lang.type_system import build_instance
if recip is None:
recip = lambda x: div(1, x)
attrs = {"fromRational": fromRational, "div": div, "recip": recip}
build_instance(Fractional, cls, attrs)
Ratio, R = (data.Ratio("a") == d.R("a", "a") & deriving(Eq))
Rational = t(Ratio, int)
instance(Fractional,
float).where(fromRational=lambda rat: float(rat[0]) / float(rat[1]),
div=lambda a, b: float(a) / float(b),
recip=lambda x: 1.0 / x)
@sig(H[(Fractional, "a")] / "a" >> "a")
def recip(a):
"""``recip :: Fractional a => a -> a``
Reciprocal fraction.
"""
return Fractional[a].recip(a)
def lcm(x, y):
"""``lcm :: Integral a => a -> a -> a``
The smallest positive integer that both `x` and `y` divide.
"""
g = gcd(x, y)
return 0 if g == 0 else (x * y) // g
from hask3.Data.Functor import Functor
from hask3.Control.Applicative import Applicative
from hask3.Control.Monad import Monad
@sig(H[(Monad, "m")] / t("m", "a") >> t("m", None))
def sequence(xs):
"""``sequence :: Monad m => [m a] -> m [a]``
Evaluate each action in the sequence from left to right, and collect the
results.
"""
raise NotImplementedError()
@sig(H[(Monad, "m")] / t("m", "a") >> t("m", None))
def sequence_(xs):
"""``sequence_ :: Monad m => [m a] -> m None``
Evaluate each action in the sequence from left to right, and ignore the
