Error

Error

error :: HasCallStack => [Char] -> a

error stops execution and displays an error message.

errorWithoutStackTrace :: [Char] -> a

A variant of error that does not produce a stack trace.

Since: base-4.9.0.0

undefined :: HasCallStack => a

A special case of error. It is expected that compilers will recognize this and insert error messages which are more appropriate to the context in which undefined appears.

throw :: Exception e => e -> a

Throw an exception. Exceptions may be thrown from purely functional code, but may only be caught within the IO monad.

assert :: Bool -> a -> a

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.