deriving-compat-0.5.9: Backports of GHC deriving extensions

Copyright(C) 2015-2017 Ryan Scott
LicenseBSD-style (see the file LICENSE)
MaintainerRyan Scott
PortabilityTemplate Haskell
Safe HaskellNone
LanguageHaskell2010

Text.Read.Deriving

Contents

Description

Exports functions to mechanically derive Read, Read1, and Read2 instances.

Synopsis

Read

deriveRead :: Name -> Q [Dec] Source #

Generates a ReadClass instance declaration for the given data type or data family instance.

deriveReadOptions :: ReadOptions -> Name -> Q [Dec] Source #

Like deriveRead, but takes a ReadOptions argument.

makeReadsPrec :: Name -> Q Exp Source #

Generates a lambda expression which behaves like readsPrec (without requiring a ReadClass instance).

makeReadPrec :: Name -> Q Exp Source #

Generates a lambda expression which behaves like readPrec (without requiring a ReadClass instance).

Read1

deriveRead1 :: Name -> Q [Dec] Source #

Generates a Read1 instance declaration for the given data type or data family instance.

deriveRead1Options :: ReadOptions -> Name -> Q [Dec] Source #

Like deriveRead1, but takes a ReadOptions argument.

makeLiftReadsPrec :: Name -> Q Exp Source #

Generates a lambda expression which behaves like liftReadsPrec (without requiring a Read1 instance).

This function is not available with transformers-0.4.

makeLiftReadPrec :: Name -> Q Exp Source #

Generates a lambda expression which behaves like liftReadPrec (without requiring a Read1 instance).

This function is only available with base-4.10 or later.

makeReadPrec1 :: Name -> Q Exp Source #

Generates a lambda expression which behaves like readPrec1 (without requiring a Read1 instance).

This function is only available with base-4.10 or later.

makeReadsPrec1 :: Name -> Q Exp Source #

Generates a lambda expression which behaves like readsPrec1 (without requiring a Read1 instance).

Read2

deriveRead2 :: Name -> Q [Dec] Source #

Generates a Read2 instance declaration for the given data type or data family instance.

This function is not available with transformers-0.4.

deriveRead2Options :: ReadOptions -> Name -> Q [Dec] Source #

Like deriveRead2, but takes a ReadOptions argument.

This function is not available with transformers-0.4.

makeLiftReadsPrec2 :: Name -> Q Exp Source #

Generates a lambda expression which behaves like liftReadsPrec2 (without requiring a Read2 instance).

This function is not available with transformers-0.4.

makeLiftReadPrec2 :: Name -> Q Exp Source #

Generates a lambda expression which behaves like liftReadPrec2 (without requiring a Read2 instance).

This function is only available with base-4.10 or later.

makeReadPrec2 :: Name -> Q Exp Source #

Generates a lambda expression which behaves like readPrec2 (without requiring a Read2 instance).

This function is only available with base-4.10 or later.

makeReadsPrec2 :: Name -> Q Exp Source #

Generates a lambda expression which behaves like readsPrec2 (without requiring a Read2 instance).

This function is not available with transformers-0.4.

ReadOptions

newtype ReadOptions Source #

Options that further configure how the functions in Text.Read.Deriving should behave.

Constructors

ReadOptions 

Fields

  • useReadPrec :: Bool

    If True:

    • Derived ReadClass instances will implement readPrec, not readsPrec, and will provide a default implementation of readListPrec in terms of readPrec.
    • If built against base-4.10 or later, derived 'Read1'/'Read2' instances will implement 'liftReadPrec'/'liftReadPrec2', not 'liftReadsPrec'/'liftReadsPrec2', and will provide default implementations of 'liftReadListPrec'/'liftReadListPrec2' in terms of 'liftReadPrec'/'liftReadPrec2'. If built against an earlier version of base, derived 'Read1'/'Read2' instances are not affected, so they will act as if this flag were False.

    If False:

    • Derived ReadClass instances will implement readsPrec.
    • Derived Read1 instances will implement readsPrec1 (if built against transformers-0.4) or liftReadsPrec (otherwise). If not built against transformers-0.4, derived Read2 instances will implement liftReadsPrec2.

    It's generally a good idea to enable this option, since readPrec and friends are more efficient than readsPrec and friends, since the former use the efficient ReadPrec parser datatype while the latter use the slower, list-based ReadS type.

Instances
Eq ReadOptions Source # 
Instance details

Defined in Text.Read.Deriving.Internal

Methods

(==) :: ReadOptions -> ReadOptions -> Bool #

(/=) :: ReadOptions -> ReadOptions -> Bool #

Ord ReadOptions Source # 
Instance details

Defined in Text.Read.Deriving.Internal

Methods

compare :: ReadOptions -> ReadOptions -> Ordering #

(<) :: ReadOptions -> ReadOptions -> Bool #

(<=) :: ReadOptions -> ReadOptions -> Bool #

(>) :: ReadOptions -> ReadOptions -> Bool #

(>=) :: ReadOptions -> ReadOptions -> Bool #

max :: ReadOptions -> ReadOptions -> ReadOptions #

min :: ReadOptions -> ReadOptions -> ReadOptions #

Read ReadOptions Source # 
Instance details

Defined in Text.Read.Deriving.Internal

Methods

readsPrec :: Int -> ReadS ReadOptions #

readList :: ReadS [ReadOptions] #

readPrec :: ReadPrec ReadOptions #

readListPrec :: ReadPrec [ReadOptions] #

Show ReadOptions Source # 
Instance details

Defined in Text.Read.Deriving.Internal

Methods

showsPrec :: Int -> ReadOptions -> ShowS #

show :: ReadOptions -> String #

showList :: [ReadOptions] -> ShowS #

defaultReadOptions :: ReadOptions Source #

ReadOptions that favor readPrec over readsPrec.

deriveRead limitations

Be aware of the following potential gotchas:

  • Type variables of kind * are assumed to have Read constraints. Type variables of kind * -> * are assumed to have Read1 constraints. Type variables of kind * -> * -> * are assumed to have Read2 constraints. If this is not desirable, use makeReadsPrec or one of its cousins.
  • The Read1 class had a different definition in transformers-0.4, and as a result, deriveRead1 implements different instances for the transformers-0.4 Read1 than it otherwise does. Also, makeLiftReadsPrec and makeLiftReadList are not available when this library is built against transformers-0.4, only 'makeReadsPrec1.
  • The Read2 class is not available in transformers-0.4, and as a result, neither are Template Haskell functions that deal with Read2 when this library is built against transformers-0.4.
  • The Read1 and Read2 classes have new methods ('liftReadPrec'/'liftReadListPrec' and 'liftReadPrec2'/'liftReadListPrec2', respectively) that were introduced in base-4.10. For now, these methods are only defined when deriving 'Read1'/'Read2' if built against base-4.10 (until transformers-compat catches up), and the corresponding make- functions are also only available when built against base-4.10.