== -package:mixed-types-num

A type family to compute Boolean equality.

Compare two streams point-wise for equality. The output stream contains the value True at a point in time if both argument streams contain the same value at that point in time.

An infix alias for Equals.

Equality relation. Defined in terms of <=.

Equality constraint, used as e.g. (x == 3) => _

Like ==, but prints a counterexample when it fails.

Implication for properties: The resulting property holds if the first argument is False (in which case the test case is discarded), or if the given property holds. Note that using implication carelessly can severely skew test case distribution: consider using cover to make sure that your test data is still good quality.

Fails the test if the two arguments provided are not equal.

Check for equality.

Examples

selectSPJ :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectSPJ = selectList [UserName ==. "SPJ" ] []

The above query when applied on dataset-1, will produce this:

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+

vertical concatenation

The ==> operator can be used to express a restricting condition under which a property should hold. It corresponds to implication in the classical logic. Note that ==> resets the quantification context for its operands to the default (universal).

The ==> operator can be used to express a restricting condition under which a property should hold. It corresponds to implication in the classical logic. Note that ==> resets the quantification context for its operands to the default (universal).

Place two diagrams (or other objects) vertically adjacent to one another, with the first diagram above the second. Since Haskell ignores whitespace in expressions, one can thus write

c
===
d

to place c above d. The local origin of the resulting combined diagram is the same as the local origin of the first. (===) is associative and has mempty as an identity. See the documentation of beside for more information.

Convenience helper. Uses pure to lift a into f a.

An exact equality comparison. For real IEEE types, two values are equivalent in the following cases:

• both values are +0;
• both values are -0;
• both values are nonzero and equal to each other (according to ==);
• both values are NaN with the same payload and sign.

For complex IEEE types, two values are equivalent if their real and imaginary parts are equivalent.

This operator produces the SQL operator =, which is used to compare values for equality. Example:

query :: UserId -> SqlPersistT IO [Entity User]
query userId = select $ do
user <- from $ table @User
where_ (user ^. UserId ==. val userId)
pure user

This would generate the following SQL:

SELECT user.*
FROM user
WHERE user.id = ?