Bug #20785
openShould `a in b, and c` `a in b, or c` `a in b, rescue c` be syntax ok?
Description
This code is accepted in parse.y but rejected in prism
tap do
a in b, and c
a in b, or c
a in b, rescue c
end
# parsed as
tap do
(a in b,;) and c
(a in b,;) or c
a in b,;
rescue c
end
I think these should be rejected like prism (parse.y accepts)
a in b, and c
a in b,
and c
tap do
a in b, rescue c
end
I think these should be accepted like parse.y (prism rejects)
tap do
a in b,
end
tap do
a in b,
rescue
end
Updated by nobu (Nobuyoshi Nakada) about 2 months ago
- Assignee set to matz (Yukihiro Matsumoto)
Updated by nobu (Nobuyoshi Nakada) about 2 months ago
- Assignee changed from matz (Yukihiro Matsumoto) to ktsj (Kazuki Tsujimoto)
Updated by Dan0042 (Daniel DeLorme) about 2 months ago
tompng (tomoya ishida) wrote:
I think these should be accepted like parse.y (prism rejects)
tap do a in b, end tap do a in b, rescue end
Can you explain your reasoning here? I'm guessing that a in b,
is parsed as a in [b,]
but a trailing comma like that is just too wild for me; it totally breaks my intuitions about Ruby syntax, and I think it should be rejected.
Updated by ktsj (Kazuki Tsujimoto) about 2 months ago
- Assignee changed from ktsj (Kazuki Tsujimoto) to matz (Yukihiro Matsumoto)
I agree with tompng's proposal.
I'm guessing that
a in b
, is parsed asa in [b,]
but a trailing comma like that is just too wild for me
in
(=>
) can be considered right assignment.
And, I think it makes sense that a trailing comma is allowed in right assignment, just as a trailing comma is allowed in normal assignment.
a => b, # one-line pattern matching as right assignment
b, = a # normal assignment
What do you think, @matz (Yukihiro Matsumoto)?
Updated by mame (Yusuke Endoh) 14 days ago
Discussed at the dev meeting. Matz says that, in principle, the trailing comma of a pattern should be allowed.
a in b, and c # Prism should accept this as `(a in b,) and c`
a in b, or c # Prism should accept this as `(a in b,) or c`
In terms of rescue after a comma, it should be handled as a modifier.
a in b, rescue c # (a in b,) rescue c
In terms of a newline after a comma, it should be handled as an end of a sentence.
a in b, # This line should be a complete sentence
and c # This is an invalid line
However, if there are implementation difficulties with the parser, he would consider compromises.
@yui-knk (Kaneko Yuichiro) @kddnewton (Kevin Newton) Do you think if matz's expectation is feasible?
Updated by kddnewton (Kevin Newton) 13 days ago
I think this resolution makes sense, we can make that work. Should we get started on it?
Updated by hsbt (Hiroshi SHIBATA) 8 days ago
- Status changed from Open to Assigned
Updated by Dan0042 (Daniel DeLorme) 8 days ago
mame (Yusuke Endoh) wrote in #note-5:
In terms of a newline after a comma, it should be handled as an end of a sentence.
a in b, # This line should be a complete sentence and c # This is an invalid line
I doubt my opinion makes any difference here, but the above makes no sense to me. I would expect this to be a valid pattern match:
a in b,
c,
d
Updated by Eregon (Benoit Daloze) 8 days ago
I think @Dan0042 (Daniel DeLorme) has a point.
For instance if I'm using some longer variables names and the array/tuple has many elements it would be natural to wrap it into two lines, but IIUC this change would break it:
if tuple in element_type, element_size, dimensions, pointer, offset, buffer_length, stride
...
end
# might be wrapped as:
if tuple in element_type, element_size, dimensions, pointer, offset,
buffer_length, stride
...
end
In the OP description, I think all cases can be very easily made clear and unambiguous by appending *
.
For example:
tap do
a in b, * and c
a in b, * or c
a in b, * rescue c
end
tap do
a in b, *
end
tap do
a in b, *
rescue
end
From that I think considering trailing comma for in
pattern matching as SyntaxError is good, as it encourages clarity and removes syntactical ambiguity (at least from a human perception).
Updated by mame (Yusuke Endoh) 5 days ago
Dan0042 (Daniel DeLorme) wrote in #note-8:
I doubt my opinion makes any difference here, but the above makes no sense to me. I would expect this to be a valid pattern match:
a in b, c, d
In RubyConf venue, I showed @matz (Yukihiro Matsumoto) your example, and it has convinced him. He changed his mind and said that a comma at the line end should continue to the next line. Your opinion made difference :-)