Re: [Chicken-users] format-modular feature request: defining one's own multi-part formats

[Kon Lovett]

On Mar 7, 2008, at 1:16 PM, Robin Lee Powell wrote:

> On Fri, Mar 07, 2008 at 01:12:06PM -0800, Kon Lovett wrote:
> > On Mar 7, 2008, at 9:08 AM, Robin Lee Powell wrote:
> >
> > > I'd like to define my own %[...%] sort of formatter using
> > > format-modular, but it seems to be impossible without copying most
> > > of the egg into my own code!  Could this be added as a general
> > > feature?
> >
> > No quite sure what you mean. Is '%' to be the escape character,
> > instead of '~'? This is possible but you would need to override
> > the  "*formatter-cond*" to provide new semantics. And all format
> > codes would need to use '%' as the escape.
> >
> > Or are you asking for a user defined multi-character escape+code
> > sequence that would coexist with the default escape+code
> > sequences? I  suppose this could be done but would require some
> > surgery.
>
> I don't think I'm asking for either of those, but I'm not sure.
>
> I'm asking how to do before-and-after escape sequences, like
> ~[...~] or ~(...~), but with my own code behind them.

You can override the existing semantics by supplying your own  
procedures. However access to the state object is very restricted to  
the public. So not all functionality that the *formatter-foo* provide  
can be reproduced by an external formatter. And the public cannot  
extend the state object, which might be necessary to implement own  
"before-and-after escape sequences".

But that doesn't mean you cannot override the existing semantics. You  
just cannot do everything.

(define (formatter-open state start params colon atsign)
  ... )

(define (formatter-close state start params colon atsign)
  ... )

(define *my-caseconv*
 `((#\( ,(formatter-function formatter-open))
   (#\) ,(formatter-function formatter-close))))

(define *formatter-mine*
  `(,*formatter-flush*
    ,*formatter-plural*
    ,*formatter-tabulate*
    ,*formatter-params*
    ,*formatter-iteration*
    ,*my-caseconv*
    ,*formatter-chars*
    ,*formatter-numbers*
    ,*formatter-cond*
    ,*formatter-indirection*
    ,*formatter-jump*
    ,*formatter-objs*
    ,*formatter-version*))

(define extd-format (make-format-function #f #\~ *formatter-mine*))

> -Robin
>
> --
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> Proud Supporter of the Singularity Institute - http://singinst.org/
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>
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Best Wishes,
Kon