verify-non-fail: A tool to verify Curry operations as non-failing

This package contains a tool to verify that all operations in a given module are non-failing, i.e., tehir evaluation does not result in a failure, if they are called with appropriate arguments. The tool automatically infers abstract call types specifying supersets of appropriate arguments.

As am example, consider the following operation to compute the last element of a given list:

last :: [a] -> a
last [x]            = x
last (_ : xs@(_:_)) = last xs

In the default mode (where types are abstracted into a set of allowed top-level constructors), the inferred call type is

last: {:}

specifying that last does not fail if the argument is a non-empty list, i.e., evaluable to some data term rooted by the list constructor :.

When an operation with such a restricted call type is used, the tool checks whether it is used in an environment which ensures its call type. For instance, the operations

head (x:xs) = x

and

tail (x:xs) = xs

have the inferred call types

head: {:}
tail: {:}

When these operations are applied, it should be ensure (in a top-level functional computation) that the actual arguments are non-empty lists, as in this operation:

readCommand :: IO ()
readCommand = do
  putStr "Input a command:"
  s <- getLine
  let ws = words s
  case null ws of True  -> readCommand
                  False -> processCommand (head ws) (tail ws)

The tool automatically verifies that the operation readCommand is non-failing.

The ideas of the implementation of this tool are described in:

M. Hanus: Inferring Non-Failure Conditions for Declarative Programs, Proc. of the 17th International Symposium on Functional and Logic Programming (FLOPS 2024), to appear in Springer LNCS, 2024

Installation:

The tool can be installed via the command

> cypm install

in the main directory of this package. This installs the executable curry-calltypes in the bin-directory of CPM.

Installation with KiCS2:

Due to an unresolved memory leak in KiCS2, it is necessary to generate different executables for each abstract domain used by the inferences. This can be done by executing

> make

in the main directory of this package. This installs the executable curry-calltypes as well as three other executables which are implicitly invoked by the main executable in the bin-directory of CPM.