[Maude-help] Re: Parsing question (answer + new question)

[Todd Wilson]

I recently asked:
> Is there a way that I can get Maude to (meta)parse literal constants
> without also automatically parsing expressions involving these?

My problem was that using metaParse(upModule(M),...), where M was 'NAT, 
'FLOAT, 'STRING, or some module like EXP that imported these together, 
didn't work, because all of the operations defined on the respective 
sorts were also imported.  (My examples had some minor errors, as well.)

Well, by doing some experiments, I found that the following works:

   fmod EXP is
     sorts Nat Float String Exp .
     subsorts Nat Float String < Exp .
     op 0 : -> Nat .
     op s_ : Nat -> Nat [iter special (
       id-hook SuccSymbol ()
       term-hook zeroTerm (0))] .
     op <Floats> : -> Float [special (id-hook FloatSymbol ())] .
     op <Strings> : -> String [special (id-hook StringSymbol ())] .

     op f : Exp -> Exp .
   endfm

Now, entering the following

   select META-LEVEL .
   red metaParse(upModule('EXP,false), 'f '`( '123 '`), 'Exp) .
   red metaParse(upModule('EXP,false), 'f '`( '1.23 '`), 'Exp) .
   red metaParse(upModule('EXP,false), 'f '`( '"123" '`), 'Exp) .
   red metaParse(upModule('EXP,false), 'f '`( '123 '+ '1 '`), 'Exp) .

gives the results I wanted, namely:

   result ResultPair: {'f['s_^123['0.Nat]],'Exp}
   result ResultPair: {'f['1.23.Float],'Exp}
   result ResultPair: {'f['"123".String],'Exp}
   result ResultPair?: noParse(3)

I copied the "special" declarations used in EXP above from 
prelude.maude, hoping that they might produce the parsing behavior I was 
looking for, and I was rewarded.  However, now, my question becomes: 
what is the link between these specials and the way Maude parses 
integers, floats, and strings?  More generally, does there exist any 
documentation of these special attributes, id-hook, op-hook, term-hook, 
etc.?  Am I creating some possible problems by using these features to 
parse literal constants in my applications?

Todd Wilson
Department of Computer Science
California State University, Fresno