Exceptions and Errors

Flix distinguishes between compilation errors, program errors, and internal errors.

Compilation Errors

Compilation errors are errors caused by malformed Flix programs, e.g. due to syntax errors, name errors, type errors, etc. A malformed Flix program should never cause the Flix compiler nor run-time to unexpectedly fail. Instead it is responsibility of the compiler to raise the appropriate compilation errors.

All compilation errors are organized in the hierarchy shown below:

  • CompilationError - super-type of all compilation errors.
    • SyntaxError - super-type of all syntax errors.
      • DuplicateAnnotation
      • DuplicateAttribute
      • DuplicateFormalArgument
      • DuplicateTag
      • NonLinearPattern
      • ...
    • ResolverError - super-type of all resolver errors.
      • DuplicateDefinition
      • IllegalVariableName
      • UnresolvedTagReference
      • ...
    • TypeError - super-type of all type errors.
      • ...
    • VerifierError - super-type of all verifier errors.
      • ...

Note that CompilationError is not a (Java) exception nor is it a (Java) error. It is simply an interface. CompilationErrors are never thrown, but are instead collected by the phases of the compiler.

Program Errors

Flix programs may themselves be erroneous. This gives rise to FlixExceptions that may be thrown at run-time as shown below:

  • java.lang.RuntimeException
    • FlixException - a common super-type for exceptions caused by Flix programs.
      • UserException - an exception explicitly thrown by the programmer.
      • MatchException - an exception thrown due to an incomplete match.
      • RuleException - an exception thrown due to an integrity rule violation.
      • SwitchException - an exception thrown due to an incomplete switch.
      • TimeoutException - an exception thrown due to a user-specified timeout.

A correct Flix program should never throw any of these exceptions.

Internal Errors

An error may occur in the Flix compiler or run-time. These errors are bugs (unexpected behaviour).

There are two types of exceptions that may be thrown:

  • java.lang.RuntimeException
    • InternalCompilerException - an exception thrown by the compiler.
    • InternalRuntimeException - an exception thrown by the run-time.

If one of these exceptions is thrown then there is a bug in Flix.

results matching ""

    No results matching ""