Re: [pdf-devel] Error management in type 4 functions

[jemarch]

Hi David.

   On the one hand, we need a list of syntax errors and a way to
   report them in `pdf_fp_func_4_new'. I think that a PDF_BADSYNTAX
   return value would works fine. But if more defailed errors are
   required, an extra argument is valid. 

A detailed report about the error is required by the standard. In this
case we can use some kind of struct to get the syntax errors.

   Anyway, the syntax
   constructions in the language are `if' and 'ifelse'. They seem
   like:

     { ... } if
     { ... } { ... } ifelse

   Indeed, whole PostScript code should be wrapped with braces
   too. So, we could report bad balanced braces and missing { ... }
   construct.

Right.

   On the other hand, we can use the same way to report errors to
   caller from `pdf_fp_func_eval'. In this case, we suggest the
   following generic interpretation errors:

     - Bad number of inputs
     - Bad number of outputs
     - Math error
     - Internal error

   Math error consists of division-by-zero, negative square root, etc,
   and internal error would be arised, for example, when the stack of
   a type 4 function overflows.

Would be useful to return more detailed information: it would be
really difficult to fix a buggy function facing something like
"Internal error". But it would be quite difficult to do it in a
generic way.

What about adding a new specific `pdf_fp_func_4_eval' function? It
would break the generic function application schema, but we can always
expand the API to ask a function its type.

What do you think?

-- 
Jose E. Marchesi  <address@hidden>
                  http://www.jemarch.net
GNU Project       http://www.gnu.org