Lambda syntax in pattern [GHC-00482]
When pattern matching, lambda expressions are not allowed as patterns to be matched against.
Examples
Lambda syntax in `case` expression
When pattern matching with a case expression, backslash (\) is not required before the pattern.
Error Message
LambdaInCase.hs:6:5: error: [GHC-00482]
Lambda-syntax in pattern.
Pattern matching on functions is not possible.
|
6 | \a -> a
| ^^^^^^^LambdaInCase.hs
Before
module LambdaInCase where
f :: Int -> Int
f x =
case x of
\a -> a
After
module LambdaInCase where
f :: Int -> Int
f x =
case x of
a -> a
Lambda syntax in pattern match
Pattern matching on functions is not possible.
Error Message
LambdaInPattern.hs:4:4: error: [GHC-00482]
Lambda-syntax in pattern.
Pattern matching on functions is not possible.
|
4 | f (\a -> a) = 0
| ^^^^^^^LambdaInPattern.hs
Before
module LambdaInPattern where
f :: (Int -> Int) -> Int
f (\a -> a) = 0
After
module LambdaInPattern where
f :: (Int -> Int) -> Int
f a = a 0