fromJust is:exact

The fromJust function extracts the element out of a Just and throws an error if its argument is Nothing.

Examples

Basic usage:

>>> fromJust (Just 1)
1

>>> 2 * (fromJust (Just 10))
20

>>> 2 * (fromJust Nothing)
*** Exception: Maybe.fromJust: Nothing
...

WARNING: This function is partial. You can use case-matching instead.

Extracts the element out of a Just and throws an error if the argument is Nothing.

The fromJust function extracts the element out of a Just and throws an error if its argument is Nothing.

Examples

Basic usage:

>>> fromJust (Just 1)
1

>>> 2 * (fromJust (Just 10))
20

>>> 2 * (fromJust Nothing)
*** Exception: Maybe.fromJust: Nothing

The fromJust function extracts the element out of a Just and throws an error if its argument is Nothing.

Examples

Basic usage:

>>> fromJust (Just 1)
1

>>> 2 * (fromJust (Just 10))
20

>>> 2 * (fromJust Nothing)
*** Exception: Maybe.fromJust: Nothing
...

Return the value of an optional value. The behavior is undefined if passed Nothing, i.e., it can return any value. Compare to fromMaybe.

>>> fromJust (sJust (literal 'a'))
'a' :: SChar

>>> prove $ \x -> fromJust (sJust x) .== (x :: SChar)
Q.E.D.

>>> sat $ \x -> x .== (fromJust sNothing :: SChar)
Satisfiable. Model:
s0 = 'A' :: Char

Note how we get a satisfying assignment in the last case: The behavior is unspecified, thus the SMT solver picks whatever satisfies the constraints, if there is one.

Convert between Just and its value.

Converts a Maybe into a value or throws an error if the Maybe is Nothing.