isJust

The isJust function returns True iff its argument is of the form Just _.

Examples

Basic usage:

>>> isJust (Just 3)
True

>>> isJust (Just ())
True

>>> isJust Nothing
False

Only the outer constructor is taken into consideration:

>>> isJust (Just Nothing)
True

Yields True iff the argument is of the form Just _.

Check if the symbolic value is not nothing.

>>> isJust (sNothing :: SMaybe Integer)
False

>>> isJust (sJust (literal "yep"))
True

>>> prove $ \x -> isJust (sJust (x :: SInteger))
Q.E.D.

Operator corresponding SQL NOT (... IS NULL) , and extended against record type.

Convert between 'Just ()' and True (see isJust).

Operator corresponding SQL NOT (... IS NULL) , and extended against record type.

A pattern for variants; can be used to both destruct a variant when in a pattern position or construct one in an expression position.

Test that a Maybe is Just.

Analogous to isJust, but for MaybeT

Returns True iff its argument is of the form "Just' _".

Returns a QGenExpr that evaluates to true when the first argument is not null