Make syntax keywords case-sensitive

[stasm]

As part of the grammar's migrations to ABNF in #347, we should decide and explicitly define whether the let, match, and when keywords are case-sensitive.

My take is to allow both all-lowercase and all-uppercase spellings and forbid any mixed-cased ones.

• Valid: let, LET
• Error: Let, lEt

[alerque]

What would be the advantage of allowing upper case at all? This complicates things for everybody and if there isn't a good use case for allowing it it will be more trouble than benefit in my opinion.

[eemeli]

I agree with @alerque. Better to continue only supporting lower-case keywords.

[stasm]

What would be the advantage of allowing upper case at all?

I've always liked the idea of using uppercase keywords to make them stand out more, a primitive replacement for syntax highlighting:

MATCH {$count :number}
 WHEN 1 {You have one notification.}
 WHEN * {You have {$count} notifications.}

OTOH, I'm not thrilled about introducing two alternative spellings to the syntax. I wanted to open this issue to document the group's take on this.

[alerque]

Well I'm exactly part of "the group", I'm just an opinionated internet user who happens to have previously written a parser for various languages (including Fluent messages in Lua) –hence the opinion that the fewer ways there are to do something that are considered right the less error prone implementations will be– and works with typography –hence the opinion that all caps look ugly– so take this with a pound of salt, but why make the language more complicated as a primitive replacement for syntax highlighting when the simpler the grammar is to parse the easier it will be write syntax highlighters? Honestly having reviewed the grammar either way MF2 doesn't look like it will take much work to spin up syntax highlighting for.

[stasm]

I meant "the group" in the most inclusive sense possible.

After spending some more time writing my own experimental lexer and parser, and given the comments above, I retract my proposal to support uppercased keywords.