@classmethod
def make_instance(self, cls, pure, ap):
pure = pure**(H[(Applicative, "f")] / "a" >> t("f", "a"))
ap = ap**(H[(Applicative, "f")] / t("f", H / "a" >> "b") >> t(
"f", "a") >> t("f", "b"))
build_instance(Applicative, cls, {"pure": pure, "ap": ap})
return
@constraint(Applicative(f))
def appAp(fn: f(a >> b), x: f(a)) -> f(b):
"""
appAp :: Applicative f => f (a -> b) -> f a -> f b
"""
return Applicative[x].ap(fn, x)
@Infix
def ap(f, x):
"""
(ap) :: Applicative f => f (a -> b) -> f a -> f b
This is infix and non-curried version of `appAp`.
"""
return Applicative[x].ap(f, x)
instance(Applicative,
List).where(pure=lambda x: L[[x]],
ap=lambda fs, xs: L[[f(x) for f in fs for x in xs]])
in imperative languages.
"""
return Monad[m].bind(m, const(k))
@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
the outer level.
"""
__id = (lambda x: x)**(H / "a" >> "a")
return bind(m, __id)
@sig(H[(Monad, "m")] / (H / "a" >> "r") >> t("m", "a") >> t("m", "r"))
def liftM(fn, m):
"""
liftM :: Monad m => (a1 -> r) -> m a1 -> m r
Promote a function to a monad.
"""
return fmap(fn, m)
instance(Monad, List).where(
bind=lambda x, fn: L[itertools.chain.from_iterable(fmap(fn, x))])
The Either type represents values with two possibilities:
a value of type `Either a b` is either `Left a` or `Right b`.
The Either type is sometimes used to represent a value which is
either correct or an error; by convention, the `Left` constructor is used
to hold an error value and the `Right` constructor is used
to hold a correct value (mnemonic: “right” also means “correct”).
"""
Left: a
Right: b
Left, Right = Either.enums
instance(Functor,
Either).where(fmap=lambda f, v: ~(caseof(v)
| m(Left(m.e)) >> Left(p.e)
| m(Right(m.ra)) >> Right(f(p.ra))))
instance(Applicative,
Either).where(pure=Right,
ap=lambda v, x: ~(caseof(v)
| m(Left(m.l)) >> Left(p.l)
| m(Right(m.r)) >> fmap(p.r, x)))
instance(Monad, Either).where(bind=lambda v, f: ~(caseof(v)
| m(Left(m.e)) >> Left(p.e)
| m(Right(m.a)) >> f(p.a)))
def in_either(fn):
"""
return not elem(x, t)
@constraint(Foldable(r))
def find(f: a >> bool, t: r(a)) -> Maybe(a):
"""
find :: Foldable r => (a -> bool) -> r a -> Maybe a
The find function takes a predicate and a structure and returns the
leftmost element of the structure matching the predicate, or Nothing if
there is no such element.
"""
return DL.find(f, toList(t))
#=============================================================================#
# Instances
instance(Foldable, List).where(foldr=DL.foldr,
foldr1=DL.foldr1,
foldl=DL.foldl,
foldl_=DL.foldl_,
foldl1=DL.foldl1,
null=DL.null,
length=DL.length,
elem=DL.elem,
minimum=DL.minimum,
maximum=DL.maximum,
sum=DL.sum,
product=DL.product)
@sig(H[(Num, "a")] / "a" >> "a" >> "a")
def mul(a, b):
"""
mul :: Num a => a -> a -> a
Multiplies two numbers.
"""
return Num[a].mul(a, b)
instance(Num, int).where(add=int.__add__,
mul=int.__mul__,
abs=int.__abs__,
signum=lambda x: -1 if x < 0 else (1 if x > 0 else 0),
fromInteger=int,
negate=int.__neg__,
sub=int.__sub__)
instance(Num, float).where(add=float.__add__,
mul=float.__mul__,
abs=float.__abs__,
signum=lambda x: -1.0
if x < 0.0 else (1.0 if x > 0.0 else 0.0),
fromInteger=float,
negate=float.__neg__,
sub=float.__sub__)
instance(Num, complex).where(add=complex.__add__,
mul=complex.__mul__,
@annotated
def unsafePerformIO(io: IO(a)) -> a:
"""
unsafePerformIO :: IO a -> a
Unsafe performs IO.
"""
return io.i0(Star)
@annotated
def unsafeFmapIO(f: a >> b, x: IO(a), n: Unit) -> b:
return f(unsafePerformIO(x))
@annotated
def unsafeApIO(fn: IO(a >> b), x: IO(a), n: Unit) -> b:
return unsafePerformIO(fn)(unsafePerformIO(x))
@annotated
def unsafeBindIO(x: IO(a), f: a >> IO(b), n: Unit) -> b:
return unsafePerformIO(f(unsafePerformIO(x)))
instance(Functor, IO).where(fmap=lambda f, x: LazyPure(unsafeFmapIO(f, x)))
instance(Applicative, IO).where(pure=pure,
ap=lambda f, x: LazyPure(unsafeApIO(f, x)))
instance(Monad, IO).where(bind=lambda x, f: LazyPure(unsafeBindIO(x, f)))
@Infix
def map(f, x):
"""
(map) :: Functor f => (a -> b) -> (f a -> f b)
This is infix and non-curried version of `fmap`.
Maps function over functor.
"""
return Functor[x].fmap(f, x)
@constraint(Functor(f))
def fmap(fn: a >> b, x: f(a)) -> f(b):
"""
fmap :: Functor f => (a -> b) -> (f a -> f b)
Maps function over functor.
"""
return Functor[x].fmap(fn, x)
@constraint(Functor(f))
def void(x: f(a)) -> f(Unit):
return fmap(const(Star), x)
instance(
Functor,
List).where(fmap=lambda fn, lst: L[builtins.map(fn, builtins.iter(lst))])
instance(Functor, TypedFunc).where(fmap=TypedFunc.__mul__)
(represented as ``Just a``), or it is empty (represented as ``Nothing``).
Using Maybe is a good way to deal with errors or exceptional cases
without resorting to drastic measures such as error.
The ``Maybe`` type is also a monad.
It is a simple kind of error monad,
where all errors are represented by ``Nothing``.
A richer error monad can be built using the ``Either`` type.
"""
Nothing : []
Just : a
Nothing, Just = Maybe.enums
instance(Functor, Maybe).where(
fmap = lambda f, x: ~(caseof(x)
| m(Just(m.a)) >> Just(f(p.a))
| m(Nothing) >> Nothing)
)
instance(Applicative, Maybe).where(
pure = Just,
ap = lambda fs, xs: ~(caseof((fs, xs))
| m((Just(m.f), Just(m.x))) >> Just(p.f(p.x))
| m((Nothing, m.x)) >> Nothing)
)
instance(Monad, Maybe).where(
bind = lambda x, f: ~(caseof(x)
| m(Just(m.a)) >> f(p.a)
| m(Nothing) >> Nothing)
)