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Re: metacircular evaluater with local environments

From: Andy Wingo
Subject: Re: metacircular evaluater with local environments
Date: Thu, 17 Feb 2011 18:56:11 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux)

Hi Klaus,

On Thu 17 Feb 2011 12:08, Klaus Schilling <address@hidden> writes:

> How does one implement a metacircular evaluator in Guile 2 with local
> environments and local-eval? Those got trashed.

A fair question, though perhaps it could have been asked more politely.

Basically, you expand a Scheme expression, then potentially do some
analysis on the expansion, then interpret the resulting expression
tree.  You have to choose a representation for environments; there is a
lot of code out there to work from, ranging from SICP to PAIP to Guile's
own (ice-9 eval).

I was feeling a bit contrarian this afternoon, so I did just that.
Attached is (ice-9 local-eval), which exports the procedure
`local-eval', the procedure-with-setter `fexpr?', and the fexpr

  (use-modules (ice-9 local-eval))
  (define env (local-eval '(let ((x 10)) (the-environment))))
  (local-eval '(* x 20) env)
  => 200
Have fun,


Attachment: local-eval.scm
Description: ice-9 local-eval


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