Hoogle Search

Within LTS Haskell 24.36 (ghc-9.10.3)

Note that Stackage only displays results for the latest LTS and Nightly snapshot. Learn more.

Exact lookup

1. readMaybe :: (Read b, StringConv a String) => a -> Maybe b

   protolude	Protolude

   Parse a string using the Read instance. Succeeds if there is exactly one valid result.

   >>> readMaybe ("123" :: Text) :: Maybe Int
   Just 123
   

   >>> readMaybe ("hello" :: Text) :: Maybe Int
   Nothing
   

2. leftToMaybe :: Either l r -> Maybe l

   protolude	Protolude.Either

   No documentation available.

3. rightToMaybe :: Either l r -> Maybe r

   protolude	Protolude.Either

   No documentation available.

4. reifyTypeWithLocals_maybe :: DsMonad q => Name -> q (Maybe Type)

   th-desugar	Language.Haskell.TH.Desugar

   Like reifyWithLocals_maybe but for types and kinds. Note that a return value of Nothing might mean that the name is not in scope, or it might mean that the full type of the name cannot be determined. (Use reifyWithLocals_maybe if you really need to tell the difference.)

5. reifyWithLocals_maybe :: DsMonad q => Name -> q (Maybe Info)

   th-desugar	Language.Haskell.TH.Desugar

   Like reify from Template Haskell, but looks also in any not-yet-typechecked declarations. To establish this list of not-yet-typechecked declarations, use withLocalDeclarations. Returns Nothing if reification fails. Note that no inferred type information is available from local declarations; bottoms may be used if necessary.

6. tupleNameDegree_maybe :: Name -> Maybe Int

   th-desugar	Language.Haskell.TH.Desugar

   Extract the degree of a tuple Name. In addition to recognizing tuple syntax (e.g., ''(,,)), this also recognizes the following:

   • ''Unit (for 0-tuples)
   • ''Solo/'MkSolo (for 1-tuples)
   • ''TupleN (for N-tuples)
   In recent versions of GHC, ''() is a synonym for ''Unit, ''(,) is a synonym for ''Tuple2, and so on. As a result, we must check for ''Unit and ''TupleN in tupleDegree_maybe to be thorough. (There is no special tuple syntax for ''Solo/'MkSolo, but we check them here as well for the sake of completeness.)

7. unboxedSumNameDegree_maybe :: Name -> Maybe Int

   th-desugar	Language.Haskell.TH.Desugar

   Extract the degree of an unboxed sum Name. In addition to recognizing unboxed sum syntax (e.g., ''()), this also recognizes ''SumN# (for unboxed N-ary sum type constructors). In recent versions of GHC, ''Sum2# is a synonym for ''(), ''Sum3# is a synonym for ''(), and so on. As a result, we must check for ''SumN# in unboxedSumNameDegree_maybe to be thorough.

8. unboxedTupleNameDegree_maybe :: Name -> Maybe Int

   th-desugar	Language.Haskell.TH.Desugar

   Extract the degree of an unboxed tuple Name. In addition to recognizing unboxed tuple syntax (e.g., ''()), this also recognizes the following:

   • ''Unit# (for unboxed 0-tuples)
   • ''Solo#/'Solo# (for unboxed 1-tuples)
   • ''TupleN# (for unboxed N-tuples)
   In recent versions of GHC, ''(##) is a synonym for ''Unit#, ''() is a synonym for ''Tuple2#, and so on. As a result, we must check for ''Unit#, and ''TupleN in unboxedTupleNameDegree_maybe to be thorough. (There is no special unboxed tuple type constructor for ''Solo#/'Solo#, but we check them here as well for the sake of completeness.)

9. unionMaybeSubsts :: [Maybe DSubst] -> Maybe DSubst

   th-desugar	Language.Haskell.TH.Desugar.Subst

   No documentation available.

10. catMaybes :: [Maybe a] -> [a]

    HaXml	Text.XML.HaXml.XmlContent.Parser

    The catMaybes function takes a list of Maybes and returns a list of all the Just values.

    Examples

    Basic usage:

    >>> catMaybes [Just 1, Nothing, Just 3]
    [1,3]
    

    When constructing a list of Maybe values, catMaybes can be used to return all of the "success" results (if the list is the result of a map, then mapMaybe would be more appropriate):

    >>> import GHC.Internal.Text.Read ( readMaybe )
    
    >>> [readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
    [Just 1,Nothing,Just 3]
    
    >>> catMaybes $ [readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
    [1,3]
    

Page 178 of many | Previous | Next