GitHub - Z-Shang/fpy: Python module for composing computations

Functional Python

For better computation composing in Python

Goals

• To bring the ability of composing computations in the functional way
• Make my life easier

No Goals

• Exact clone of Haskell
• Blazing fast / super efficient

Python is Already Amazing, Why Bother?

• Because I can
• Python may be amazing in some field, but sucks from the functional perspective

Python Sucks, Why Bother?

• Because I can
• Python is still used in my work place

Install

With pip:

pip install fppy

Control:

Functor fpy.control.functor

Given Functors f, g:

• __fmap__ :: f a -> (a -> b) -> f b
• __ntrans__ :: f a -> (f a ~> g b) -> g b

Operators:

• | = __fmap__
• & = __ntrans__

Functions:

• fmap = __fmap__

NTrans (Natrual Transform) fpy.control.natural_transform

Given Functors f, g:

• __trans__ :: f a ~> g b

Applicative : Functor fpy.control.applicative

No new trait comparing to functor, liftA2 is defined using fmap

Monad : Applicative fpy.control.monad

Given Monad m:

• __bind__ :: m a -> (a -> m b) -> m b

Operators:

• >> = __bind__

Do Notation:

• @do(Monad) enables do notation in the decorated function, where the explicit return statement will be treated as ret from the given Monad type, if no return statement is given, the last element on the stack will be returned.
• name <- computation binds the computation to the following block, calling the __bind__ method of the monad object returned from computation with the name name.
• (name1, name2, ..., namen) <- computation works in the similar way as the single name binding, this applys the binding function to the tuple contained within the monad object instead of calling the function directly.
• name1, name2, ..., namen <- computation same as above

Data

Maybe : Monad fpy.data.maybe

Types:

• Maybe[T]
• Just[T] : Maybe[T]
• Nothing[T] : Maybe[T]

Functions:

• isJust :: Maybe[T] -> bool
• isNothing :: Maybe[T] -> bool
• fromJust :: Maybe[T] -> T
• fromMaybe :: T -> Maybe[T] -> T
• maybe :: S -> (T -> S) -> Maybe[T] -> S
• mapMaybe :: (T -> Maybe[S]) -> List[T] -> List[S]

Either : Monad fpy.data.either

Types:

• Either[T]
• Left[T] : Either[T]
• Right[T] : Either[T]

Forgetful : Monad (Forgetful Functor) fpy.data.forgetful

Types:

• Under[T] Under similar to Haskell's Identity monad

Cont : Monad fpy.data.cont

Types:

• Cont[T, R]

Functions:

• cont :: (A -> B) -> Cont[A, B]
• runCont :: Cout[B, C] -> C

Functions:

Given functor f: forget: NTrans[F, B, Under, T] :: f b ~> Under[T]

Utility Functions fpy.data.function

• id_ :: T -> T
• const :: T -> A -> T
• flip :: (B -> A -> T) -> A -> B -> T
• fix :: (A -> A) -> A
• on :: (B -> B -> T) -> (A -> B) -> A -> A -> T

Slightly Dependent Utilities

-- not so well typed

NArg :: Nat -> Type
NArg (S Z) = A
NArg (S n) = A -> (NArg n)

NTpl :: (n:Nat) -> (NArg n) -> Type
NTpl (S Z) A =( A,)
NTpl (S n) (A -> NArg n) = cons A (NTpl n (NArg n))

• constN :: (n:Nat) -> A -> (NArg n) -> A
• uncurryN :: (n:Nat) -> args:(NArg n) -> A -> ((NTpl n args) -> A)

Composable

Composable fpy.composable.composable

• __compose__

Operators:

• ^ = __compose__

Transparent fpy.composable.transparent

• __underlying__ Delegate an attribute access to an underlying object

Function fpy.composable.function

Types:

• func : Composable
• SignatureMismatchError
• NotEnoughArgsError

Collections fpy.composable.collections

Types:

• Seq : func
• Map : func

Functions:

• transN(n, f, it) := it[n] = f(it[n])
• getN(n, it) := it[n]
• setN(n, v, it) := it[n] = v
• eqN(n, it, x) := it[n] == x
• mapN(n, fn, lsts) := map(fn, zip(lst1, lst2 ... lstn))
• of_(v1 ... vn) := _ in (v1 ... vn)
• is_(t) := isinstance(_, t)
• and_(a, b) := a(_) and b(_)
• or_(a, b) := a(_) or b(_)
• to(dst, src) := dst(src)
• apply(fn) := fn(*a, **k)
• fwd_ = Under.ret

Predefined Vars:

• trans0
• trans1
• get0
• get1
• set0
• set1
• eq0
• eq1
• mp1
• mp2

Parsec

Parsec fpy.parsec.parsec

Types:

• parser[S, T] :: [S] -> Either [S] ([T] * [S])

Operators:

• * = parser.timeN
• + = parser.concat
• | = parser.choice
• >> = parser.parseR
• << = parser.parseL

Functions:

• one :: (S -> bool) -> parser[S, S]
• neg :: (S -> bool) -> parser[S, S]
• just_nothing :: parser[S, T]
• pmaybe :: parser[S, T] -> parser[S, T]
• many :: parser[S, T] -> parser[S, T]
• many1 :: parser[S, T] -> parser[S, T]
• ptrans :: parser[S, T] -> (T -> Y) -> parser[S, Y]
• peek :: parser[S, T] -> parser[S, T]
• skip :: parser[S, T] -> parser[S, T]
• pseq :: [S] -> parser[S, T]
• inv :: parser[S, T] -> parser[S, T]

Dependencies

• bytecode

License

GPL3+