On 4/17/12 4:57 PM, Graydon Hoare wrote:
On 12-04-17 04:01 PM, Niko Matsakis wrote:
Apologies in advance.
Ha! Apologies in return, then, as at least the first bit I'm kinda sour
on. The rest I'm just confused over.
This requires arbitrary lookahead to disambiguate from tuples.
This bit in particular. Really really don't want to cross the bridge to
arbitrary lookahead in the grammar.
Yes, I don't like this either.
Note that these two are not problematic: "-> foo" (no lookahead) or "x
-> x + 1" (one token lookahead). Only multi-arity functions require
arbitrary lookahead: "(x, y) -> x + y". This could be fixed with some
sort of sigil: "\(x, y) -> x + y" or bars: "|x, y| -> x + y". I kind of
like the latter, although I'm told that JavaScript developers balked
when TC39 proposed it.
2. You may omit the last argument of a function that expects a closure
using a syntax like the following:
vec.iter: x { ... }
This is ambiguous. Is "{ spawn: { hello() } }" a call to a function
"spawn" with a block argument or a record literal with "spawn" as the key?
This can be repaired by requiring the parentheses:
for [ 1, 2, 3 ].each(): x {
...
}
spawn(): {
...
}
Or it can be repaired by requiring some sort of prefix for record literals.
I guess I'm having a hard time seeing the motive. Is it a preference for
parens over braces? We could probably support (|pat| expr) as a lambda
just as well as {|pat| expr} -- parser can see the transition point to
pattern grammar -- though it loses the "transitions to multi-line
easily" aspect I mention in point #2 above..
To me (just IMHO) there are three main issues with the current syntax:
(1) In curly-brace-structured languages, "{" generally ends the line.
(2) "{||" reads like line noise.
(3) Programmers don't seem to like Ruby/Smalltalk-like bars much in
languages that aren't in the syntactic tradition of Smalltalk. I didn't
realize this when I proposed it... that said, I do like the way "|x, y|
x + y" looks.
Anyway, just a little more shameless bikeshedding...
Patrick
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