change "when" to "if" in pattern guards

[nikomatsakis]

I suggest we replace the word "when" in pattern guards with the word "if". This is the only place that "when" appears in our grammar and so it would seem more consistent:

alt foo {
    pat(a, b) if cond { ... }
    pat(a, b) { ... }
}

[brson]

I'm ok with this.

[kud1ing]

Is it possible that for this one only needs to

• adjust parse_alt_expr() in parser.rs
• adjust print_expr() in pprust.rs
• fix the using codes and tests

?

[nikomatsakis]

Yes.

[brson]

The parser will need to temporarily accept both 'when' and 'if', then we do a snapshot, then remove 'when'.

[brson]

@Lenny222 are you working on this?

[kud1ing]

@brson I considered it, but haven't started yet. Someone can go ahead if he wants to.

[thoughtpolice]

I will implement this. I have most of the changes done but need to test it.

[thoughtpolice]

@brson The above change makes the parser accept both when and if in alt patterns. It changes the pretty printer to unambiguously print if in alt patterns as well. I have run the entire test suite and it seems OK. Feel free to push to the try branch first.

I have the remaining changes to the code under src to change when -> if (which felt surprisingly small actually) but I cannot test them until a snapshot is created with this change. Does this commit look OK and if so, can you merge and snapshot? I will follow up with the 2 remaining commits (change usages throughout code, and remove 'when' from the parser) afterwords.

[brson]

lgtm. I will let you know when the snapshot is done.

[brson]

We will also need to update the language docs and the tutorial

[thoughtpolice]

OK. I will do that too and put the commits in this issue before I close it.

[brson]

Snapshots are done.

[thoughtpolice]

@brson The 3 commits mentioned above should take care of the rest of this issue. They replace all occurrences of when with if, remove parser support, and fix up the documentation and tutorial. I ran the testsuite (especially after removing parser support) and everything seems A-OK

I believe with all of that taken care of, once merged, that should close this issue.

Note: I re-pushed my issue-1396 branch after you merged my last change, so you may have to re-pull it if you had it pulled already.

[brson]

Thanks! Merged.