KerMeta Type System and well-formedness rules
Build date: 10-October-2005
Table of Contents
KerMeta does not support operation specialization but only invariant operation overriding.
TODO: Present the model
TODO: Briefly discuss function types.
A class type C1can be a sub-type of some Class TypeVariable ProductType or SelfType
This section details the static computation of type of each kind of expression.
|
Expression |
Type |
|---|---|
|
VoidLiteral |
result := kermeta::standard::Void |
|
BooleanLiteral |
result := kermeta::standard::Boolean |
|
IntegerLiteral |
result := kermeta::standard::Integer |
|
StringLiteral |
result := kermeta::standard::String |
|
TypeLiteral |
if expression.typeref.upper == 1 then result := expression.typeref.type else if expression.typeref.unique and expression.typeref.ordered then result := OrderedSet<expression.typeref.type> end if expression.typeref.unique and not expression.typeref.ordered then result := Set<expression.typeref.type> end if not expression.typeref.unique and expression.typeref.ordered then result := Sequence<expression.typeref.type> end if not expression.typeref.unique and not expression.typeref.ordered then result := Bag<expression.typeref.type> end end |
Loop expression
Constraints :
TypeOf(Loop.stopCondition) <: kermeta::standard::Boolean
Returned Type :
In the literature 3 solution are defined for the return value of a loop expression:
Nothing. This is the simplest solution.
The object returned by the expression “body” for the last iteration.
The collection of object returned by the expression “body” for all iterations.
Among these solution, and for the sake of simplicity, we have chosen to implement the first solution in KerMeta.
|
Expression |
Type |
|---|---|
|
Loop |
result := kermeta::standard::Void |
Block expression
A block is contains a set of statements and a set of rescue block. Each rescue block handles a particular type of exception. The type of an exception can only be a Class.
Constraints :
Block.rescueBlock.exceptionType.type <: kermeta::structure::Class
Block.rescueBlock.exceptionType.upper = 1
Returned Type :
Two alternatives exists in the literature :
Nothing. This is the simplest solution.
The object returned by the last statement of the block.
In KerMeta we have chosen the second solution because it is the choice made in the OCL. If a rescue block is executed, the block expression returns Void.
|
Expression |
Type |
|---|---|
|
Block |
TypeOf( Block.statement.last ) |
Conditional expression
Constraints :
TypeOf(Conditional.stopCondition) <: kermeta::standard::Boolean
Returned Type :
2 solutions
Nothing. This is the simplest solution.
Support for union types
The first solution 1 has been rejected because it does not allow some very convenient OCL-like expressions.
|
Expression |
Type |
|---|---|
|
Conditional |
UNION ( TypeOf( Conditional.thenBody ), TypeOf( Conditional.elseBody ) ) |
The scope of a variable is the block in which it is defined.
A variable can be initialized with an initialization expression. If there is no initialization expression then its value is initialized to void.
Constraints :
TypeOf(VariableDecl.initialization) <: AsType( VariableDecl.type )
Returned Type :
|
Expression |
Type |
|---|---|
|
VariableDecl |
AsType( VariableDecl.type ) |
Call expression allows reading / writing variable and properties but also calling operations, super-operations and lambda expressions.
Call variable / Call result
A Call variable represents a call to an operation parameter, a interpreter variable or a local variable. In any case, the type of this variable might be either a simple type or a function type.
If it is a simple type, the returned value of the expression is the value of the variable: the type of the expression is the type of the variable.
If the type of the variable is a function type then there are two possible behaviour depending on the presence of parameters. In no parameters are supplied then the returned value of the expression is the function but if parameter are provided, the function is applied and the value returned by the expression is the value returned by the function. In that case the return type of the expression is the return type of the function.
Constraints :
Presence of parameters => function types
Number of parameters
Type of parameters
SelfExpression
The self expression allow accessing the current instance. The object returned by a self expression is the instance in the context of which the operation is executed. The type of this object can be any type associated with the class definition in which the operation is defined.
Thus the type of a self expression is obtained by binding all type variables of the class to the least derived compatible type. If the type variable has a superType then this superType is used, otherwise the type Object is used.
CallFeature
CallFeature expression allows calling operation and reading/writing features. If no target is specified the self is used.
Returned Type :
|
Expression |
Type |
|---|---|
|
CallVariable |
XXX |