From: John Cowan
Date: Tue, 5 Jun 2007 16:04:52 -0400
Subject: [Formal] Identifiers beginning with "->" considered useless

Submitter: John Cowan
Issue type: Defect
Priority: Minor
Component:  Lexical syntax
Report version: 5.93
Summary: Identifiers beginning with "->" considered useless.

R5.93RS extends the lexical syntax of R5RS identifiers to allow
them to begin with "->", presumably for the sake of the R5.91
procedures "->exact" and "->inexact".  The former names of these
procedures, "exact->inexact" and "inexact->exact", were misleading,
since they accepted both exact and inexact arguments.  However,
5.93 renamed these "exact" and "inexact" per formal comment #203.

I believe that the principles given in that comment are of a general
nature such that names like "->foo" are always better given as "foo".
While I am no fan of arbitrary restrictions on names, I am not in favor
of arbitrary exceptions either.  I suggest that "->" prefixes should be
removed for R6RS.


RESPONSE:

Many existing Scheme implementations prior to R5.93RS already
supported identifiers starting with ->.  (Many readers would classify
any lexeme as an identifier starting with - for which `string->number'
returns #f.)  As a result, a significant amount of otherwise portable
Scheme code used identifiers starting with ->, which are a convenient
choice for many names.  Therefore, R5.93RS legalizes these
identifiers.  The separate production in the grammar is not
particularly elegant.  However, designing a more elegant production
that does not overlap with representations of number objects or other
lexeme classes has proved to be surprisingly difficult.  Therefore,
the comment has not been adopted.