Safe Haskell	None
Language	Haskell98

Text.Reform.Proof

Contents

transformations (proofs minus the proof).
Various Proofs

Description

This module defines the Proof type, some proofs, and some helper functions.

A Proof does three things:

verifies that the input value meets some criteria
optionally transforms the input value to another value while preserving that criteria
puts the proof name in type-signature where the type-checker can use it

Synopsis

data Proof m error proof a b = Proof {
- proofName :: proof
- proofFunction :: a -> m (Either error b)
}
prove :: Monad m => Form m input error view q a -> Proof m error proof a b -> Form m input error view proof b
transform :: Monad m => Form m input error view anyProof a -> Proof m error proof a b -> Form m input error view () b
transformEitherM :: Monad m => Form m input error view anyProof a -> (a -> m (Either error b)) -> Form m input error view () b
transformEither :: Monad m => Form m input error view anyProof a -> (a -> Either error b) -> Form m input error view () b
data NotNull = NotNull
notNullProof :: Monad m => error -> Proof m error NotNull [a] [a]
data Decimal = Decimal
data RealFractional = RealFractional
data Signed a = Signed a
decimal :: (Monad m, Eq i, Num i) => (String -> error) -> Proof m error Decimal String i
signedDecimal :: (Monad m, Eq i, Real i) => (String -> error) -> Proof m error (Signed Decimal) String i
realFrac :: (Monad m, RealFrac a) => (String -> error) -> Proof m error RealFractional String a
realFracSigned :: (Monad m, RealFrac a) => (String -> error) -> Proof m error (Signed RealFractional) String a

Documentation

data Proof m error proof a b Source #

A Proof attempts to prove something about a value.

If successful, it can also transform the value to a new value. The proof should hold for the new value as well.

Generally, each Proof has a unique data-type associated with it which names the proof, such as:

data NotNull = NotNull

Constructors

Proof
Fields proofName :: proof name of the thing to prove proofFunction :: a -> m (Either error b) function which provides the proof

prove :: Monad m => Form m input error view q a -> Proof m error proof a b -> Form m input error view proof b Source #

apply a Proof to a Form

transformations (proofs minus the proof).

transform :: Monad m => Form m input error view anyProof a -> Proof m error proof a b -> Form m input error view () b Source #

transform a Form using a Proof, and the replace the proof with ().

This is useful when you want just want classic digestive-functors behaviour.

transformEitherM :: Monad m => Form m input error view anyProof a -> (a -> m (Either error b)) -> Form m input error view () b Source #

transform the Form result using a monadic Either function.

transformEither :: Monad m => Form m input error view anyProof a -> (a -> Either error b) -> Form m input error view () b Source #

transform the Form result using an Either function.

Various Proofs

data NotNull Source #

proof that a list is not empty

Constructors

NotNull

notNullProof :: Monad m => error -> Proof m error NotNull [a] [a] Source #

prove that a list is not empty

data Decimal Source #

proof that a String is a decimal number

Constructors

Decimal

data RealFractional Source #

proof that a String is a Real/Fractional number

Constructors

RealFractional

data Signed a Source #

proof that a number is also (allowed to be) signed

Constructors

Signed a

decimal Source #

Arguments

:: (Monad m, Eq i, Num i)
=> (String -> error)	create an error message (`String` is the value that did not parse)
-> Proof m error Decimal String i

read an unsigned number in decimal notation

signedDecimal :: (Monad m, Eq i, Real i) => (String -> error) -> Proof m error (Signed Decimal) String i Source #

read signed decimal number

realFrac :: (Monad m, RealFrac a) => (String -> error) -> Proof m error RealFractional String a Source #

read RealFrac number

realFracSigned :: (Monad m, RealFrac a) => (String -> error) -> Proof m error (Signed RealFractional) String a Source #

read a signed RealFrac number