(read-enable 'copy)

(read-enable 'copy)

[Ludovic Courtès]

Hello,

What is the `copy' reader option about?  Looking at the code, it seems
that this has to do with source properties but I fail to understand the
point of this option.

Thanks,
Ludovic.


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Re: (read-enable 'copy)

[Neil Jerram]

ludovic.courtes@laas.fr (Ludovic Courtès) writes:

> Hello,
>
> What is the `copy' reader option about?  Looking at the code, it seems
> that this has to do with source properties but I fail to understand the
> point of this option.

It tells Guile to take a copy of the source expression as originally
read, before it might be transformed by the syntax transformer, macro
expansion or memoization.  Then the backtrace can show the actual
original expression.

Whereas, without the copy option, the backtrace shows a guess
(admittedly, usually correct) at the original expression which is
obtained by unmemoizing the evaluator's internal representation.

         Neil




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