Text.Show.Combinators

Combinators for Show

The combinators below can be used to write Show instances.

The following type illustrates the common use cases.

data MyType a
  = C a a                   -- a regular constructor
  | a :+: a                 -- an infix constructor
  | R { f1 :: a, f2 :: a }  -- a record

infixl 4 :+:

instance Show a => Show (MyType a) where
  showsPrec = flip precShows where
    precShows (C a b) = showCon C @| a @| b
    precShows (c :+: d) = showInfix' ":+:" 4 c d
    precShows (R {f1 = e, f2 = f}) =
      showRecord R ("f1" .=. e &| "f2" .=. f)

Documentation

module Text.Show

type PrecShowS = Int -> ShowS

Type of strings representing expressions, parameterized by the surrounding precedence level.

This is the return type of flip showsPrec.

showCon :: String -> PrecShowS

Show a constructor.

showApp :: PrecShowS -> PrecShowS -> PrecShowS infixl 2

Show a function application.

(@|) :: Show a => PrecShowS -> a -> PrecShowS infixl 2

Show a function application.

This is an infix shorthand for showApp when the argument type is an instance of Show.

showF @| x = showApp showF (flip showsPrec x)

showInfix :: String -> Int -> PrecShowS -> PrecShowS -> PrecShowS

Show an applied infix operator with a given precedence.

showInfix' :: (Show a, Show b) => String -> Int -> a -> b -> PrecShowS

Show an applied infix operator with a given precedence.

This is a shorthand for showInfix when the arguments types are instances of Show.

showInfix' op prec x y =
  showInfix op prec (flip showsPrec x) (flip showsPrec y)

type ShowFields = ShowS

Strings representing a set of record fields separated by commas. They can be constructed using (.=.) and (@|), or using showField and appendFields.

showRecord :: String -> ShowFields -> PrecShowS

Show a record. The first argument is the constructor name. The second represents the set of record fields.

showField :: String -> PrecShowS -> ShowFields

Show a single record field: a field name and a value separated by '='.

(.=.) :: Show a => String -> a -> ShowFields infixr 8

Show a single record field: a field name and a value separated by '='.

This is an infix shorthand for showField when the value type is an instance of Show.

field .=. x = showField field (flip showsPrec x)

noFields :: ShowFields

Empty set of record fields.

appendFields :: ShowFields -> ShowFields -> ShowFields infixr 1

Separate two nonempty sets of record fields by a comma.

(&|) :: ShowFields -> ShowFields -> ShowFields infixr 1

An infix synonym of appendFields.