| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell2010 |
Control.Exception.Assert.Sugar
Contents
Description
Syntactic sugar that improves the usability of assert
and error. The original assert function is here re-exported
for convenience.
Make sure to enable assertions for your cabal package, e.g., by setting
ghc-options: -fno-ignore-asserts
in your .cabal file. Otherwise, some of the functions will have no effect at all.
Synopsis
- assert :: Bool -> a -> a
- blame :: Show v => Bool -> v -> Bool
- showFailure :: Show v => String -> v -> String
- swith :: String -> v -> (String, v)
- allB :: Show v => (v -> Bool) -> [v] -> Bool
- twith :: Text -> b -> (Text, b)
- failure :: Show a => (forall x. Bool -> x -> x) -> a -> b
- forceEither :: Show a => (forall x. Bool -> x -> x) -> Either a b -> b
Documentation
assert :: Bool -> a -> a Source #
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 v => Bool -> v -> Bool infix 1 Source #
If the condition fails, display the value blamed for the failure. Used as in
assert (age < 120 `blame` age) $ savings / (120 - age)
showFailure :: Show v => String -> v -> String infix 2 Source #
A helper function for error. To be used as in
case xs of 0 : _ -> error $ "insignificant zero" `showFailure` xs
Fixing the first argument to String instead of anything Showable
prevents warnings about defaulting, even when OverloadedStrings
extension is enabled.
swith :: String -> v -> (String, v) infix 2 Source #
Syntactic sugar for the pair operation, to be used for blame as in
assert (age < 120 `blame` "age too high" `swith` age) $ savings / (120 - age)
Fixing the first component of the pair to String prevents warnings
about defaulting, even when OverloadedStrings extension is enabled.
allB :: Show v => (v -> Bool) -> [v] -> Bool Source #
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 (<= height) [yf, y1, y2])
DEPRECATED
twith :: Text -> b -> (Text, b) infix 2 Source #
Deprecated: consider using swith instead, for simplicity, because GHC optimizes lazy String constants very well.
Syntactic sugar for the pair operation, to be used for blame as in
assert (age < 120 `blame` "age too high" `twith` age) $ savings / (120 - age)
Fixing the first component of the pair to Text prevents warnings
about defaulting, even when OverloadedStrings extension is enabled.
failure :: Show a => (forall x. Bool -> x -> x) -> a -> b infix 1 Source #
Deprecated: use error and showFailure instead, now that error prints source positions.
Like error, but shows the source position (in newer GHCs
error shows source position as well, hence deprecation)
and also the value to blame for the failure. To be used as in
case xs of 0 : _ -> assert `failure` (xs, "has an insignificant zero")
forceEither :: Show a => (forall x. Bool -> x -> x) -> Either a b -> b infix 1 Source #
Deprecated: use 'either (error . show) id' instead, now that error prints source positions.
Assuming that Left signifies an error condition,
check the Either value and, if Left is encountered,
fail outright and show the error message (in newer GHCs
error shows source position as well, hence deprecation). Used as in
assert `forceEither` parseOrFailWithMessage code