Re: [Scheme-reports] Issues with R7RS draft 8 section 7.1.1 <symbol element>

On Sun, Jan 13, 2013 at 4:29 AM, David A. Wheeler <dwheeler@x> wrote:

I just found some issues in R7RS draft 8 section 7.1.1
[...]
But these productions have two issues:
1. Having <symbol element> list double-quote is pointless, since that
is already covered by "<any character other than <vertical line> or \>".
2. More importantly, the call to <string element> creates a useless
ambiguity, because string element's <any character other than " or \>
ALSO matches almost all the same characters.

Thanks for catching this. Note that there was another issue which

is that we hadn't updated the draft after removing support for raw

symbol escapes outside of vertical bars.

I've fixed both of these, moving the mnemonic escapes up into

the identifier section so there are no forward-references from

symbol syntax to strings.

Note that we voted to add both hex escapes and mnemonic

escapes (like \t and \n) to symbols, but said nothing about

the trailing whitespace escapes, so these are left unspecified

for symbols.

The relevant definitions are:

<identifier> : <initial> <subsequent>*

| <vertical line> <symbol element>* <vertical line>

| <peculiar identifier>

<symbol element> :

| <inline hex escape> | <mnemonic escape> | \|

<mnemonic escape> : \a | \b | \t | \n | \r

<string> : " <string element>* "

| <mnemonic escape> | \" | \\

| \ <intraline whitespace>* <line ending> \ <intraline whitespace>*

| <inline hex escape>

Alex