Re: [CoFI] CASL Concrete Syntax

[pdmosses@brics.dk]

Till wrote:
> Some minor points.
> ...
> page 5:
> I do not understand the syntax of TERMs and MIXED-TERMs.
> It seems that much more than wanted is allowed by the grammar.
> 
> [Moreover, it is desirable to reinstate the usual productions for
>  function and predicate application---and insist that they have higher
>  precedence that the sequence of MIXED-TERMs, so that when a
>  specification makes no use at all of mixfix applications, the
>  recognized grouping of terms and atomic formulae is correct straight
>  away.  This should facilitate obtaining the concrete syntax of
>  sublanguages that do not allow mixfix notation.  I'll send the details
>  in a separate message, later today.  --PDM]

Here it is.  Replace:

         FORMULA         ::= ...
                           | QUAL-PRED-NAME ( TERMS )
                           | MIXED-TERM MIXED-TERM...
                           | ...                 

         TERM            ::= MIXED-TERM...

         MIXED-TERM      ::= ...
                           | ( TERMS )

by:

         FORMULA         ::= ...
      !                    | PRED-SYMB ( TERMS )
                           | SIMPLE-TERM SIMPLE-TERM...
                           | ...                 

         TERM            ::= SIMPLE-TERM...

         SIMPLE-TERM      ::= ...
      !			   | OP-SYMB ( TERMS )
      !                    | ( TERM )

Note that SIMPLE-TERM (was MIXED-TERM) is the subsort of TERM that
forbid mixfix applications at the outermost level; one can get the
sublanguage not allowing mixfix applications at all by replacing
"SIMPLE-TERM..." by just "SIMPLE-TERM" above, and removing the
production for FORMULA that involves SIMPLE-TERM.

The disambiguation rules are simply that "PRED-SYMB ( TERMS )" and
"OP-SYMB ( TERMS )" have higher precedence than "( TERM )".

I hope this clarifies the intended syntax.  It's been prototyped in
ASF+SDF, but more with respect to accepting legal specifications than
for rejecting illegal ones.  If you think it should be tightened up
further, please suggest how...

Peter
_________________________________________________________________
=========   Peter D. MOSSES              Associate Professor, PhD
==== ====   BRICS                        mailto:pdmosses@brics.dk
=========   Dept. of Computer Science    == pdmosses@daimi.aau.dk
==== ====   University of Aarhus         http://www.brics.dk/~pdm
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