Quail-Language

Quail Specification

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Chapter 10: Exceptions and errors

• Quail Specification
  • Chapter 10: Exceptions and errors
    • 10.1 Definitions
    • 10.2 Using exceptions
      • 10.2.1 Built-in exceptions
      • 10.2.2 Creating exceptions
      • 10.2.3 Throwing exceptions
      • 10.2.4 Catching exceptions
      • 10.2.5 Behaviour

10.1 Definitions

Exception is a Quail object that represents an error. Exception can be thrown interrupting execution and caught when thrown to resume execution.

10.2 Using exceptions

10.2.1 Built-in exceptions

Exception class	Meaning
AssertionException	Thrown when assert fails
CircularDependencyException	Thrown when circular import is detected (see $9.3.3)
DerivationException	Thrown when derivation is impossible
Exception	Base class for all exceptions
IndexOutOfBoundsException	Thrown when you try to access invalid index
IOException	Thrown when Java’s java.lang.IOException is thrown
IterationNotStartedException	Thrown when you try to access next element, but not started iterating
IterationStopException	Thrown when iteration reached end
UnsuitableTypeException	Thrown when value is of unsuitable type for this operation
UnsuitableValueException	Thrown when value is unsuitable for this operation
UnsupportedConversionException	Thrown when requesting conversion is not supported
UnsupportedIterationException	Thrown when iteration is requested, but not supported by this object
UnsupportedOperationException	Thrown when requested operation is not supported
UnsupportedStepSubscriptException	Thrown when subscript with step is not supported
UnsupportedSubscriptException	Thrown when subscript is not supported
UnsupportedUnaryOperationException	Thrown when requested operation is not supported

10.2.2 Creating exceptions

You can inherit exception classes to create your own exceptions

class MyException like Exception {
    constructor (this, string message) {
        this.message = "MyException says: " + message
    }
}

10.2.3 Throwing exceptions

To throw an exception use following syntax:

throw Exception() % { "message" = "This is an exception" }

throw MyException("Hello!")

10.2.4 Catching exceptions

To catch an exception use following syntax:

try {
    # erroneous code
} catch as e {
    # exception placed into e
}

try {
    # erroneous code
} catch IOException as e {
    # only catches IOException, all other are left untouched
}

try {
    # erroneous code
} catch IOException as e {
    # only catches IOException, all other are left untouched
} catch as e {
    # fallback
}

10.2.5 Behaviour

When exception is thrown, a RuntimeStriker (inherits java.lang.Exception) is issued. Try-catch blocks neutralize RuntimeStrikers which are carrying exceptions.