Safe Haskell | None |
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Tools for specifying assertions. A step towards contracts.
Actually, a bunch of hacks wrapping the original `assert`

function,
which is the only easy way of obtaining source locations.

- assert :: Bool -> a -> a
- blame :: Show a => Bool -> a -> Bool
- failure :: Show a => (Bool -> b -> b) -> a -> b
- allB :: Show a => (a -> Bool) -> [a] -> Bool
- checkM :: (Show a, Monad m) => (Bool -> m () -> m ()) -> (c -> Bool) -> a -> c -> m ()
- trueM :: (Show a, Monad m) => (Bool -> m () -> m ()) -> a -> Bool -> m ()
- falseM :: (Show a, Monad m) => (Bool -> m () -> m ()) -> a -> Bool -> m ()

# Documentation

If the first argument evaluates to `True`

, then the result is the
second argument. Otherwise an `AssertionFailed`

exception is raised,
containing a `String`

with the source file and line number of the
call to `assert`

.

Assertions can normally be turned on or off with a compiler flag
(for GHC, assertions are normally on unless optimisation is turned on
with `-O`

or the `-fignore-asserts`

option is given). When assertions are turned off, the first
argument to `assert`

is ignored, and the second argument is
returned as the result.

blame :: Show a => Bool -> a -> BoolSource

If the condition fails, display the value blamed for the failure. Used as in

assert (c /= 0 `blame` c) $ 10 / c

failure :: Show a => (Bool -> b -> b) -> a -> bSource

Like `error`

, but shows the source location and also
the value to blame for the failure. To be used as in:

assert `failure` ((x1, y1), (x2, y2), "designate a vertical line")

allB :: Show a => (a -> Bool) -> [a] -> BoolSource

Like `all`

, but if the predicate fails, blame all the list elements
and especially those for which it fails. To be used as in:

assert (allB (>= 0) [yf, xf, y1, x1, y2, x2])

checkM :: (Show a, Monad m) => (Bool -> m () -> m ()) -> (c -> Bool) -> a -> c -> m ()Source

Check that the value returned from a monad action satisfies a predicate. Reports source location and the suspects. Drops the value.