Allow case insensitive matching of literals

[dmajda]

Right now, matching literals case-insensitively is hard and ugly. For example, the only way to match "select" case-insensitively is:

select = [Ss][Ee][Ll][Ee][Cc][Tt]

Having one global flag for case-insensitivity would create problems when parts of a language is case-sensitive and another case-insensitive. Also combining languages (a feature I am thinging about for later) would be harder. Better way would be to signify case insensitivity for each literal separately, e.g. like this:

select = "select"i

[izuzak]

i really like this proposal ("select"i). however, limiting the flag to just literals will prove problematic in large grammar files which are used for case insensitive matching - adding "i" to the end of each literal is very error-prone, imo.

could the "i" flag work in a way that it may be applied not just to literals but to any expression? for example:

newRule = select#
select = "select1" / "select2"

where "#" is the flag for case insensitive matching and in this case it is applied to everything matched by the select rule (both "select1" and "select2"). of course, the "#" flag could also be applied to literals themselves, e.g. "select1"#.

[dmajda]

I implemented the i suffix proposal for literals and also for character classes.

I chose this solution because any solution that would mark whole parts of the grammar as case-insensitive would have problems with recursive rules (probably requiring forbidding in such cases) and generally introduce complexity and non-local effects. This is something I'd like to avoid.

An easy way to avoid forgetting i when writing literals is to extract all case-insensitive keywords into separate rules and group them together like this:

select = "select"i
from   = "from"i
where  = "where"i
...

[s3u]

Has this fix ever made it into the online site or npm modules?

[dmajda]

@s3u Not yet. Will be included in PEG.js 0.7.0.

[JanSemorad]

DOWNLOAD
= "DOWNLOAD"
/ D O W N L O A D {return "DOWNLOAD" }

D = [Dd]
O = [Oo]
W = [Ww]
N = [Nn]
L = [Ll]
A = [Aa]

[jtenner]

None of this change is documented. I've been using peg.js for years now and I had no idea this feature exists.

[futagoza]

@JanSemorad Is there a point to that post?

@jtenner Thank for pointing this out. I've been using PEG.js for 4 years now, and for some reason I always knew the feature was there but somehow never realised it wasn't documented 😆 Opened a new issue for this, see #518