Defining a category

A category definition looks like

$$\bf Category \bf == \bf with \bf\{ \bf\}$$

or like

$$\bf Category \bf == \bf with \bf\{ \bf\}$$

where in each case

• the first Identifier must be a new identifier,
• the second Identifier must refer to an existing category,
• FunctionDeclarationSequence is a sequence (possibly empty) of function declarations, each declaration ending with a ;.

The specifications of the so-defined category consists of the function declarations on the right of the with key-word, plus the specifications of the existing category, if present.

A function declaration looks like

$$\bf ( \bf ) \bf ->$$ (1)

where

• Identifier must be a new identifier,
• TypeSequence is a sequence (possibly empty) of % or type identifiers, separated by commas,
• Type is % or a type identifier, or () (which means void).

such that

• either % is the first element in TypeSequence (and the function is viewed as a method)
• or % is not the first element in TypeSequence but Type is % (and the function is viewed as a creator).

The above constraint is not required in ALDOR and is meant here to ease the type checking in ALLCOT. We shall return to this later.

Some remarks regarding the non-terminal Type. There are circumstances where Type cannot be % or () . For instance, we shall never need to declare of variable of type () . Moreover, in the definition of the main function, we shall never need to declare of variable of type %. These special cases can be treated at the level of the type checking.

Observe that the empty list () can be generated by two different ways: as an empty list of parameter of a function or as the void type.