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Submitter's Name: Alan Watson
Submitter's Email Address: [EMAIL PROTECTED]
Type of Issue: Enhancement
Priority: Minor
R6RS Component: Lexer
Version of Report: 5.92
One-Sentence Summary: Allow inline hex escapes anywhere
Full description of the issue:
The current report allows inline hex escapes (\x...;) in symbol literals
and string literals and has a similar but different scheme for hex
escapes in character literals. This allows one to write a program that
uses non-ASCII symbols, string, and character literals using only ASCII
characters.
The current report allows non-ASCII characters to appear in symbol
literals, string literals, character literals, whitespace, and in
comments. (I think that is an exhaustive list.)
Many current Schemes have lexers written for ASCII (or Latin-1)
character sets. Conversion of these lexers to the new standard would be
easier if the report allowed inline hex escapes to appear anywhere in
Scheme code. One would simply add a pass before the lexer that converts
non-ASCII characters to inline hex escapes and converts inline hex
escapes representing ASCII characters to ASCII characters, and would
modify the lexer to handle inline hex escapes as appropriate.
For this scheme to work, the report must be modified, because a lexer so
modified cannot distinguish a hex escape that was subsituted for a
non-ASCII character from one that was present originally.
An alternative approach that would achieve more or less the same effect
would be to allow inline hex escapes anywhere, but outside of strings
and symbols require that they represent only non-ASCII characters. I do
not favor this restriction.
This modification would also create a means to portably interchange
programs using only ASCII, although I'm not sure if this is especially
useful given UTF-8.
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