Copyright	(c) Sjoerd Visscher 2020
Maintainer	sjoerd@w3future.com
Stability	experimental
Portability	non-portable
Safe Haskell	None
Language	Haskell2010

Data.DeriveLiftedInstances

Contents

Deriving instances
Derivators for any class
Derivators for algebraic classes
Creating derivators
Orphan instances

Description

Synopsis

deriveInstance :: Derivator -> Q Type -> Q [Dec]
idDeriv :: Derivator
newtypeDeriv :: Name -> Name -> Derivator -> Derivator
isoDeriv :: Q Exp -> Q Exp -> Derivator -> Derivator
apDeriv :: Derivator -> Derivator
tupleDeriv :: Derivator -> Derivator -> Derivator
unitDeriv :: Derivator
showDeriv :: Derivator
data ShowsPrec
- = ShowsPrec (Int -> String -> String)
- | ShowOp2 Fixity (Int -> String -> String)
- | ShowOp1 Fixity (Int -> String -> String)
data Derivator = Derivator {
- res :: Q Exp -> Q Exp
- op :: Name -> Q Exp -> Q Exp
- arg :: Type -> Q Exp -> Q Exp
- var :: (Q Exp -> Q Exp -> Q Exp) -> Q Exp -> Q Exp
- ap :: Q Exp -> Q Exp -> Q Exp
}

Deriving instances

deriveInstance :: Derivator -> Q Type -> Q [Dec] Source #

Derive the instance with the given Derivator and the given instance head.

The instance head can be passed as a template haskell type quotation, for example:

{-# LANGUAGE TemplateHaskell #-}
[t| Num ShowsPrec |]
[t| forall a. Num a => Num [a] |]
[t| forall a b. (Num a, Num b) => Num (a, b) |]

Derivators for any class

idDeriv :: Derivator Source #

The identity Derivator. Not useful on its own, but often used as input for other Derivators.

newtypeDeriv :: Name -> Name -> Derivator -> Derivator Source #

Given how to derive an instance for a, and the names of a newtype wrapper around a, newtypeDeriv creates a Derivator for that newtype. Example:

newtype Ap f a = Ap { getAp :: f a } deriving Show
deriveInstance (newtypeDeriv 'Ap 'getAp idDeriv) [t| forall f. Functor f => Functor (Ap f) |]

> fmap (+1) (Ap [1,2,3])
Ap {getAp = [2,3,4]}

isoDeriv :: Q Exp -> Q Exp -> Derivator -> Derivator Source #

Given how to derive an instance for a, and two functions of type a `->` b and b `->` a, isoDeriv creates a Derivator for b. (Note that the 2 functions don't have to form an isomorphism, but if they don't, the new instance can break the class laws.) Example:

newtype X = X { unX :: Int } deriving Show
mkX :: Int -> X
mkX i = X (mod i 10)
deriveInstance (isoDeriv [| mkX |] [| unX |] idDeriv) [t| Num X |]

> mkX 4 ^ 2
X {unX = 6}

Derivators for algebraic classes

Algebraic classes are type classes where all the methods return a value of the same type, which is also the class parameter. Examples from base are Num and Monoid.

apDeriv :: Derivator -> Derivator Source #

Given how to derive an instance for a, apDeriv creates a Derivator for f a, when f is an instance of Applicative. Example:

deriveInstance (apDeriv idDeriv) [t| forall a. Num a => Num [a] |]

> [2, 3] * [5, 10]
[10, 20, 15, 30]

tupleDeriv :: Derivator -> Derivator -> Derivator Source #

Given how to derive an instance for a and b, tupleDeriv creates a Derivator for (a, b).

deriveInstance (tupleDeriv idDeriv idDeriv) [t| forall a b. (Num a, Num b) => Num (a, b) |]

> (2, 3) * (5, 10)
(10, 30)

unitDeriv :: Derivator Source #

A Derivator for ().

showDeriv :: Derivator Source #

Derive instances for ShowsPrec. Example:

deriveInstance showDeriv [t| Num ShowsPrec |]

> show ((6 * 7) ^ 2 :: ShowsPrec)
"fromInteger 6 * fromInteger 7 * (fromInteger 6 * fromInteger 7)"

data ShowsPrec Source #

Helper for showing infix expressions

Constructors

ShowsPrec (Int -> String -> String)
ShowOp2 Fixity (Int -> String -> String)
ShowOp1 Fixity (Int -> String -> String)

Instances

Instances details

Bounded ShowsPrec Source #
Instance details Defined in Data.DeriveLiftedInstances Methods minBound :: ShowsPrec # maxBound :: ShowsPrec #
Floating ShowsPrec Source #
Instance details Defined in Data.DeriveLiftedInstances Methods pi :: ShowsPrec # exp :: ShowsPrec -> ShowsPrec # log :: ShowsPrec -> ShowsPrec # sqrt :: ShowsPrec -> ShowsPrec # (**) :: ShowsPrec -> ShowsPrec -> ShowsPrec # logBase :: ShowsPrec -> ShowsPrec -> ShowsPrec # sin :: ShowsPrec -> ShowsPrec # cos :: ShowsPrec -> ShowsPrec # tan :: ShowsPrec -> ShowsPrec # asin :: ShowsPrec -> ShowsPrec # acos :: ShowsPrec -> ShowsPrec # atan :: ShowsPrec -> ShowsPrec # sinh :: ShowsPrec -> ShowsPrec # cosh :: ShowsPrec -> ShowsPrec # tanh :: ShowsPrec -> ShowsPrec # asinh :: ShowsPrec -> ShowsPrec # acosh :: ShowsPrec -> ShowsPrec # atanh :: ShowsPrec -> ShowsPrec # log1p :: ShowsPrec -> ShowsPrec # expm1 :: ShowsPrec -> ShowsPrec # log1pexp :: ShowsPrec -> ShowsPrec # log1mexp :: ShowsPrec -> ShowsPrec #
Fractional ShowsPrec Source #
Instance details Defined in Data.DeriveLiftedInstances Methods (/) :: ShowsPrec -> ShowsPrec -> ShowsPrec # recip :: ShowsPrec -> ShowsPrec # fromRational :: Rational -> ShowsPrec #
Num ShowsPrec Source #
Instance details Defined in Data.DeriveLiftedInstances Methods (+) :: ShowsPrec -> ShowsPrec -> ShowsPrec # (-) :: ShowsPrec -> ShowsPrec -> ShowsPrec # (*) :: ShowsPrec -> ShowsPrec -> ShowsPrec # negate :: ShowsPrec -> ShowsPrec # abs :: ShowsPrec -> ShowsPrec # signum :: ShowsPrec -> ShowsPrec # fromInteger :: Integer -> ShowsPrec #
Show ShowsPrec Source #
Instance details Defined in Data.DeriveLiftedInstances.Internal Methods showsPrec :: Int -> ShowsPrec -> ShowS # show :: ShowsPrec -> String # showList :: [ShowsPrec] -> ShowS #
Semigroup ShowsPrec Source #
Instance details Defined in Data.DeriveLiftedInstances Methods (<>) :: ShowsPrec -> ShowsPrec -> ShowsPrec # sconcat :: NonEmpty ShowsPrec -> ShowsPrec # stimes :: Integral b => b -> ShowsPrec -> ShowsPrec #
Monoid ShowsPrec Source #
Instance details Defined in Data.DeriveLiftedInstances Methods mempty :: ShowsPrec # mappend :: ShowsPrec -> ShowsPrec -> ShowsPrec # mconcat :: [ShowsPrec] -> ShowsPrec #

Creating derivators

data Derivator Source #

To write your own Derivator you need to show how each part of a method gets lifted. For example, when deriving an instance for type a of the following methods:

meth0 :: a
meth1 :: Int -> a
meth2 :: a -> Either Bool a -> Int
meth3 :: Maybe [a] -> a

the resulting template haskell declarations are (pseudo code):

meth0 = $res ($op "meth0" meth0)
meth1 a = $res (($op "meth1" meth1) `$ap` ($arg Int a))
meth2 v0 v1 = (($op "meth2" meth2) `$ap` ($var fold0 v0)) `$ap` ($var fold1 v1)
  where
    fold0 _ f = f
    fold1 map f = [| $map $f |]
meth3 v2 = $res (($op "meth2" meth2) `$ap` ($var fold2 v2))
  where
    fold2 map f = [| $map ($map $f) |]

Constructors

Derivator
Fields res :: Q Exp -> Q Exp Convert the result of the method op :: Name -> Q Exp -> Q Exp Convert the method (still unapplied to any arguments) arg :: Type -> Q Exp -> Q Exp Convert an argument var :: (Q Exp -> Q Exp -> Q Exp) -> Q Exp -> Q Exp Convert a variable ap :: Q Exp -> Q Exp -> Q Exp Apply an argument or variable to the method

Orphan instances

Bounded ShowsPrec Source #
Instance details Methods minBound :: ShowsPrec # maxBound :: ShowsPrec #
Floating ShowsPrec Source #
Instance details Methods pi :: ShowsPrec # exp :: ShowsPrec -> ShowsPrec # log :: ShowsPrec -> ShowsPrec # sqrt :: ShowsPrec -> ShowsPrec # (**) :: ShowsPrec -> ShowsPrec -> ShowsPrec # logBase :: ShowsPrec -> ShowsPrec -> ShowsPrec # sin :: ShowsPrec -> ShowsPrec # cos :: ShowsPrec -> ShowsPrec # tan :: ShowsPrec -> ShowsPrec # asin :: ShowsPrec -> ShowsPrec # acos :: ShowsPrec -> ShowsPrec # atan :: ShowsPrec -> ShowsPrec # sinh :: ShowsPrec -> ShowsPrec # cosh :: ShowsPrec -> ShowsPrec # tanh :: ShowsPrec -> ShowsPrec # asinh :: ShowsPrec -> ShowsPrec # acosh :: ShowsPrec -> ShowsPrec # atanh :: ShowsPrec -> ShowsPrec # log1p :: ShowsPrec -> ShowsPrec # expm1 :: ShowsPrec -> ShowsPrec # log1pexp :: ShowsPrec -> ShowsPrec # log1mexp :: ShowsPrec -> ShowsPrec #
Fractional ShowsPrec Source #
Instance details Methods (/) :: ShowsPrec -> ShowsPrec -> ShowsPrec # recip :: ShowsPrec -> ShowsPrec # fromRational :: Rational -> ShowsPrec #
Num ShowsPrec Source #
Instance details Methods (+) :: ShowsPrec -> ShowsPrec -> ShowsPrec # (-) :: ShowsPrec -> ShowsPrec -> ShowsPrec # (*) :: ShowsPrec -> ShowsPrec -> ShowsPrec # negate :: ShowsPrec -> ShowsPrec # abs :: ShowsPrec -> ShowsPrec # signum :: ShowsPrec -> ShowsPrec # fromInteger :: Integer -> ShowsPrec #
Semigroup ShowsPrec Source #
Instance details Methods (<>) :: ShowsPrec -> ShowsPrec -> ShowsPrec # sconcat :: NonEmpty ShowsPrec -> ShowsPrec # stimes :: Integral b => b -> ShowsPrec -> ShowsPrec #
Monoid ShowsPrec Source #
Instance details Methods mempty :: ShowsPrec # mappend :: ShowsPrec -> ShowsPrec -> ShowsPrec # mconcat :: [ShowsPrec] -> ShowsPrec #