pizza questions

[Joel Reymont]

I'm looking to modify the Pizza dialog example [1] to enable lookup of
pizza toppings, etc. outside of the grammar.

For example, I may want to store the available toppings in a database.

I can't make sense of the following categories, though

cat
[Item] ;
[Topping]{1}

Why is it necessary to separately list Item and Topping enclosed in brackets?

Shouldn't just Item and Topping be sufficient?

Also, what is the meaning of {1} in topping above?

Thanks, Joel

[1] http://www.cse.chalmers.se/alumni/bringert/xv/pizza/Pizza.gf

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[Aarne Ranta]

These are shorthands for list categories. Thus

  cat [Topping] {1} ;

is expanded to the rules

  cat ListTopping ;

  fun BaseTopping : Topping -> ListTopping ;

  fun ConsTopping : Topping -> ListTopping -> ListTopping ;

The number {1} says that the base case has 1 element. The default is 0, used in [Item].

It seems the on-line reference manual doesn't explain this shorthand, sorry for that. The book does, though, and the on-line manual must of course be updated.

  Aarne.