[plt-scheme] (v4) wildcard not allowed in expression

From: YC (yinso.chen at gmail.com)
Date: Mon Jun 23 22:04:51 EDT 2008

Thanks Jos for the explanation.

I do not grok how prohibiting a wildcard appearing in a template makes it
useful.  Is there a place that explains the rationale behind the change?  I
tried searching the docs but are not successful so far except for a short
description of what you've said in


On Mon, Jun 23, 2008 at 6:47 PM, Jos Koot <jos.koot at telefonica.net> wrote:

>  Correct. _ has become a wild-card that is bound to a syntax that does not
> want to be called. You can no longer use _ like other symbols. Hence the
> wild card may appear in a pattern, but you should not use it in a template.
> That is in R6RS or PLT 4. In 371 _ was just a symbol like any other one. Why
> in Pretty Big it still works as an ordinary symbol in old fashion, I don't
> know.
> If you want a symbol that is associated with the name of the syntax use
> anything else than a wild-card. The wild-card is not bound to a pattern
> element (except may be in Pretty Big, I don't know)
> Jos
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