Potential R7RS small erratum: escaped identifiers

[Daphne Preston-Kendal]

We got this report on the R7RS issue tracker:
<https://codeberg.org/scheme/r7rs/issues/230>

Reproducing the content here for completeness:

> 👋 I think there might be a (rather minor) inconsistency in the grammar of R7RS-small, regarding escaped identifiers (`|foo bar|`). In "2.1 Identifiers", it says (emphasis mine):
>
>> Any character, including whitespace characters, but excluding the backslash and vertical line characters, can appear verbatim in such an identifier. In addition, characters can be specified using either an 〈inline hex escape〉 or _the same escapes available in strings_.
>
> But later in the grammar:
>
> ```
> 〈string〉 −→ " 〈string element〉* "
> 〈string element〉 −→ 〈any character other than " or \〉
> | 〈mnemonic escape〉 | \" | \\ | \|
> | \〈intraline whitespace〉*〈line ending〉
> 〈intraline whitespace〉*
> | 〈inline hex escape〉
>
>
> 〈identifier〉 −→ 〈initial〉 〈subsequent〉*
> | 〈vertical line〉 〈symbol element〉* 〈vertical line〉
> | 〈peculiar identifier〉
>
> 〈symbol element〉 −→
> 〈any character other than 〈vertical line〉 or \〉
> | 〈inline hex escape〉 | 〈mnemonic escape〉 | \|
> ```
>
> So the escapes `\\` and `\"` are missing from the `symbol element` non-terminal (though maybe only the former provides any value).

(I haven’t reviewed this yet, I’m just forwarding it on.)



Daphne

[Alex Shinn]

Thanks for forwarding the issue Daphne!

Definitely \| is missing from the formal syntax.

I think the spirit of the prose in 2.1 is that "the same escapes available in strings" should be interpreted in the context of the | (vertical bar) delimiter, so support for \" is not implied.

In practice implementations are likely to allow \<char> for any <char> in general though.

--

Alex

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[Alex Shinn]

Sorry, this is already listed as errata 5: https://small.r7rs.org/wiki/R7RSSmallErrata/