all package:hedgehog

Determines whether all elements of the structure satisfy the predicate.

Examples

Basic usage:

>>> all (> 3) []
True

>>> all (> 3) [1,2]
False

>>> all (> 3) [1,2,3,4,5]
False

>>> all (> 3) [1..]
False

>>> all (> 3) [4..]
* Hangs forever *

Optional command configuration.

A sequential prefix of actions to execute, with two branches to execute in parallel.

Check a group of properties in parallel. Warning: although this check function runs tests faster than checkSequential, it should be noted that it may cause problems with properties that are not self-contained. For example, if you have a group of tests which all use the same database table, you may find that they interfere with each other when being run in parallel. Using Template Haskell for property discovery:

tests :: IO Bool
tests =
checkParallel $$(discover)

With manually specified properties:

tests :: IO Bool
tests =
checkParallel $ Group "Test.Example" [
("prop_reverse", prop_reverse)
]

A set of callbacks which provide optional command configuration such as pre-condtions, post-conditions and state updates.

Executes the prefix actions sequentially, then executes the two branches in parallel, verifying that no exceptions are thrown and that there is at least one sequential interleaving where all the post-conditions are met. To generate parallel actions to execute, see the parallel combinator in the Hedgehog.Gen module.

Generates a random input for the test by running the provided generator.

Generates a random input for the test by running the provided generator. This is a the same as forAll but allows the user to provide a custom rendering function. This is useful for values which don't have a Show instance.

The first branch.

The second branch.

The sequential prefix.

Given the initial model state and set of commands, generates prefix actions to be run sequentially, followed by two branches to be run in parallel.

Make a generator smaller by scaling its size parameter.

Generates a Unicode character, including noncharacters and invalid standalone surrogates: '0'..'1114111'

Generates a random input for the test by running the provided generator.

Generates a random input for the test by running the provided generator. This is a the same as forAllT but allows the user to provide a custom rendering function. This is useful for values which don't have a Show instance.

CallStacks are a lightweight method of obtaining a partial call-stack at any point in the program. A function can request its call-site with the HasCallStack constraint. For example, we can define

putStrLnWithCallStack :: HasCallStack => String -> IO ()

as a variant of putStrLn that will get its call-site and print it, along with the string given as argument. We can access the call-stack inside putStrLnWithCallStack with callStack.

>>> :{
putStrLnWithCallStack :: HasCallStack => String -> IO ()
putStrLnWithCallStack msg = do
putStrLn msg
putStrLn (prettyCallStack callStack)
:}

Thus, if we call putStrLnWithCallStack we will get a formatted call-stack alongside our string.

>>> putStrLnWithCallStack "hello"
hello
CallStack (from HasCallStack):
putStrLnWithCallStack, called at <interactive>:... in interactive:Ghci...

GHC solves HasCallStack constraints in three steps:

1. If there is a CallStack in scope -- i.e. the enclosing function has a HasCallStack constraint -- GHC will append the new call-site to the existing CallStack.
2. If there is no CallStack in scope -- e.g. in the GHCi session above -- and the enclosing definition does not have an explicit type signature, GHC will infer a HasCallStack constraint for the enclosing definition (subject to the monomorphism restriction).
3. If there is no CallStack in scope and the enclosing definition has an explicit type signature, GHC will solve the HasCallStack constraint for the singleton CallStack containing just the current call-site.

CallStacks do not interact with the RTS and do not require compilation with -prof. On the other hand, as they are built up explicitly via the HasCallStack constraints, they will generally not contain as much information as the simulated call-stacks maintained by the RTS. A CallStack is a [(String, SrcLoc)]. The String is the name of function that was called, the SrcLoc is the call-site. The list is ordered with the most recently called function at the head. NOTE: The intrepid user may notice that HasCallStack is just an alias for an implicit parameter ?callStack :: CallStack. This is an implementation detail and should not be considered part of the CallStack API, we may decide to change the implementation in the future.

Return the current CallStack. Does *not* include the call-site of callStack.

Perform some computation without adding new entries to the CallStack.