> : catalan(n) n ifZero: [ 1 ] else: [ catalan(n 1-) 2 n * 1- * 2 * n 1+ / ] ; >(from http://rosettacode.org/wiki/Catalan_numbers#Oforth) it seems like, if what you say is true, then : must be a parsing word that not only reads "catalan(n)" but also somehow decomposes it in a way and sets things up such that the later call "catalan(n 1-)" is understood correctly even though "catalan", "(", and "n" are not separated by whitespace. It very much looks like there is some tokenization going on.
You are right, I forgot to say that the following characters stop the parsing of a name : { } [ ] ( ) | This is a difference with a classical Forth interpreter.
The call to catalan( n 1- ) is just sugar, the interpreter replace it by : n 1- catalan. It is not related to how : works.
The following definition is exactly the same : : catalan( n ) n ifZero: [ 1 ] else: [ n 1- catalan 2 n * 1- * 2 * n 1+ / ] ;
>Also, is "ifZero:" really a separate message from "else:", i.e., or is "ifZero:" also a parsing word that looks if what follows is a well-formed expression followed by "else:"?
Yes, ifZero: is really a separate word from else: . It is the same structure as the Forth structures :
if then
if else then
the if does not know if there will be a then or a else and is not a parsing word. This is the same with ifZero:. It is not a parsing word and it is the else: word that do the job.
By the way, you can see the definition of all these words in the prelude.of file (they are all written in Oforth).
>If you have parsing words everywhere, you have a parser. It may not be a classical parser where everything is written in one place, but it's a parser nonetheless.
Not much more than in a classical Forth, where you find lots of parsing words too. I have no problem to call this "a parser". I'am just saying that there is nothing different from a classic Forth.
> I don't think there's anything wrong with implementing a Smalltalk dialect in Forth, with lots and lots of parsing words, and compiling the Smalltalk surface syntax to stack-based Forth code on the fly. That's lovely. It's just a shame to expose the underlying Forth in the surface syntax...
All the ifTrue:, else:, ... are not parsing words. There are not "lots and lots" of parsing words, at least not much more than in a classical Forth. There is nothing to do with the Smalltalk messages mecanism. There is nothing more here than a "if else then" Forth structure...