Text.Read.Deriving

Exports functions to mechanically derive Read, Read1, and Read2 instances. Note that upstream GHC does not have the ability to derive Read1 or Read2 instances, but since the functionality to derive Read extends very naturally Read1 and Read2, the ability to derive the latter two classes is provided as a convenience.

Read

deriveRead :: Name -> Q [Dec]

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

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

Like deriveRead, but takes a ReadOptions argument.

makeReadsPrec :: Name -> Q Exp

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

makeReadPrec :: Name -> Q Exp

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

Read1

deriveRead1 :: Name -> Q [Dec]

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

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

Like deriveRead1, but takes a ReadOptions argument.

makeLiftReadsPrec :: Name -> Q Exp

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

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

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

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

Read2

deriveRead2 :: Name -> Q [Dec]

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]

Like deriveRead2, but takes a ReadOptions argument.

This function is not available with transformers-0.4.

makeLiftReadsPrec2 :: Name -> Q Exp

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

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

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

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

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

Read ReadOptions

Defined in Text.Read.Deriving.Internal

Methods

readsPrec :: Int -> ReadS ReadOptions

readList :: ReadS [ReadOptions]

readPrec :: ReadPrec ReadOptions

readListPrec :: ReadPrec [ReadOptions]

Show ReadOptions

Defined in Text.Read.Deriving.Internal

Methods

showsPrec :: Int -> ReadOptions -> ShowS

show :: ReadOptions -> String

showList :: [ReadOptions] -> ShowS

Eq ReadOptions

Defined in Text.Read.Deriving.Internal

Methods

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

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

Ord ReadOptions

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

defaultReadOptions :: ReadOptions

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.