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Difference between revisions of "VIATRA2/Examples/VTCL/TypeChecking"
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=== Typed variables within ASM rules === | === Typed variables within ASM rules === | ||
| − | In ASM rules, types can be assigned to variables within the '''let''' rule with the following syntax '''VarName : TypeConst = InitValue'''. The following example demonstrates two typical type errors identified by the typechecker. | + | In ASM rules, types can be assigned to variables within the '''let''' rule with the following syntax '''VarName : TypeConst = InitValue'''. Here the type constant '''TypeConst''' should be a valid element of the model space, which can be resolved at compile time. |
| + | |||
| + | The following example demonstrates two typical type errors identified by the typechecker. | ||
<source lang="text"> | <source lang="text"> | ||
machine typechecking_errors { | machine typechecking_errors { | ||
rule main() = | rule main() = | ||
| − | let X : datatypes.Integer = 0 in | + | let X : datatypes.Integer = 0, |
| + | Y : datatypes.Integer = "oops0" // Type error: | ||
| + | in | ||
seq { | seq { | ||
// Type error: operation '*' undefined for types ('Integer', 'String') | // Type error: operation '*' undefined for types ('Integer', 'String') | ||
Revision as of 10:17, 25 May 2009
Contents
Overview: Type checking
Type checking is introduced to the VTCL language in a backward compatible way. This means that any existing VTCL transformation should compile without modification.
As the main extension of the language, one can add type information to
- all variables defined locally with the let rule
- a parameter of an ASM rule, graph pattern or graph transformation rule
- for the parameters and return values of ASM functions
Then the VIATRA2 parser checks if these variables are used in a type conformant way.
Typed variables within ASM rules
In ASM rules, types can be assigned to variables within the let rule with the following syntax VarName : TypeConst = InitValue. Here the type constant TypeConst should be a valid element of the model space, which can be resolved at compile time.
The following example demonstrates two typical type errors identified by the typechecker.
machine typechecking_errors {
rule main() =
let X : datatypes.Integer = 0,
Y : datatypes.Integer = "oops0" // Type error:
in
seq {
// Type error: operation '*' undefined for types ('Integer', 'String')
update X = X * "oops1";
// Type error: type incompatible assignment: left value is of type 'Integer', right value is of type 'String'
update X = X + "oops2";
// This is correct
update X = X + 3;
}
}Typed variables in ASM functions
Typed variables in graph patterns
Error messages
The following error messages are issued by the type checker
- Operator '-' is undefined for the argument type ('datatypes.String'): issued when checking an ASM term
- Operator '*' is undefined for the argument types ('datatypes.String', 'datatypes.String'): issued when checking an ASM term
- The type 'uml2.metamodel.Classifier' of actual parameter is not compatible with the type 'uml2.metamodel.Class' of symbolic parameter 'C'. See the definition of 'myPattern' : issued when calling a graph pattern using the find construct
- The type 'uml2.metamodel.Classifier' of variable reference is not compatible with the type 'uml2.metamodel.Class' of its definition.: issued in ASM rules or in the body of graph patterns
- Type incompatible assignment: left value is of type 'datatypes.String', right value is of type 'datatypes.Integer' : issued in case of an update rule
- Type incompatible initialization: expecting a term of type 'datatypes.String' instead of 'datatypes.Integer' : issued when initializing an ASM function
--Varro.mit.bme.hu 11:02, 25 May 2009 (UTC)