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Re: new function or modify read

This page is part of the web mail archives of SRFI 38 from before July 7th, 2015. The new archives for SRFI 38 contain all messages, not just those from before July 7th, 2015.

Marc Feeley <feeley@xxxxxxxxxxxxxxxx> writes:
> So in the end the "write-showing-shared" procedure still needs
> parameters.  

Depends. I am quite happy with it as it sits and am using the
reference implementation to dump suffix-trees of 200+ KB documents.
The suffix trees are actually circular gecause of Scheme's top-level
union type and I'm using a home-brewed shared-string library based on
SRFI-13, but write-showing-shared makes the data structure readable,
which is more than anybody's implementation of write does. It's
especially nice to think that I could use the same format to read the
suffix-trees back in later. I'm pretty tired of maintaining custom I/O
procedures that are only marginally faster than generating the data
structure in the first place.

> We don't yet know how many we need (and probably never
> will as the need for new features never ceases to grow).  This is why
> an API based on dynamically bound parameter objects is needed.
> Alternatively, explicit keyword parameters could also be used:
>    (write obj port shared: #t pretty: #t)

I could live with that, but I have mixed feelings about keyword
parameters. 'Nuff said.

> I have also found readtables to be a good way to package up the
> parameters that are used by "write" and "read".  The readtable
> specifies the external representation and "write" and "read" use
> the readtable when generating the external representation or
> when parsing an object.  

> With readtables you would have:
> or
>    (let ((rt (readtable-copy (current-readtable))))
>      (readtable-allow-sharing-set! rt #t)
>      (readtable-pretty-print-set! rt #t)
>      (write obj port readtable: rt))

I think I like this idea even better. Although I'd ditch the keyword
and just make it a second optional parameter.

david rush
Scheme: Because pure lambda calculus gets tedious after a while.
	-- Anton van Straaten (the Scheme Marketing Dept from c.l.s)