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Re: Fix reader options for R6RS `get-datum'

From: Noah Lavine
Subject: Re: Fix reader options for R6RS `get-datum'
Date: Mon, 17 Dec 2012 14:30:29 -0500


On Mon, Dec 17, 2012 at 2:05 PM, Andreas Rottmann <address@hidden> wrote:
I think this is my assumption that you seem to disagree on: by using the
binding of `read' from `(rnrs io simple)', instead of the one provided
by Guile's core, the writer of the code using that binding has declared
that he wishes `read' to adhere to R6RS.

I actually disagree with this assumption too, but let me explain why. I think there are some situations where it is right and some where it is wrong.

A program will want strict R6RS semantics (as Rotty says) if it is, for instance, reading from a data file in a strictly-defined format. In that case, it might have written its parser assuming an R6RS-compliant `read' function, and it could fail if it gets an extended `read'.

However, the R6RS reader would be wrong for a program that wants to, say, read a file of Scheme code as S-expressions and manipulate it. The program would have to be written using R6RS libraries to be portable, but the right thing for it to do in any particular Scheme implementation is to read exactly the same syntax as that implementation. (This is a bit of a contrived example, but I hope you can see my point that some programs don't want strict R6RS semantics as much as they want to integrate with whatever extensions their host implementation has made to `read', and that what they really want is a portable way to access the built-in `read'.)

If you believe both of these examples, then programs need to be able to choose their own meaning. Perhaps the solution is a procedure like `strict-r6rs-read-options' for programs that want that, or alternatively `native-read-options' for programs that don't.


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