Here's a total bikeshed. Apologies in advance:
There's been some criticism of Rust's syntax for being too brace-heavy.
I've been thinking this for a while. Here's a minimal delta on the
current syntax to address this:
Examples:
// before:
if foo() == "bar" { 10 } else { 20 }
// after:
if foo() == "bar" then 10 else 20
// or:
if foo() == "bar" { 10 } else { 20 }
// before:
alt foo() {
"bar" { 10 }
"baz" { 20 }
"boo" { 30 }
}
// after:
alt foo() {
"bar" => 10,
"baz" => 20,
"boo" => 30
}
// or:
alt foo() {
"bar" { 10 }
"baz" { 20 }
"boo" { 30 }
}
BNF:
if ::== "if" expr ("then" expr | block) ("else" expr)?
alt ::== "alt" expr "{" (arm* last-arm) "}"
arm ::== block-arm | pat "=>" expr ","
last-arm ::== block-arm | pat "=>" expr ","?
block-arm ::== pat block
You can think of it this way: We insert a "then" before the
then-expression of each if; however, you can omit it if you use a block.
We also insert a "=>" before each expression in an alt arm and a "," to
separate expressions from subsequent patterns; however, both can be
omitted if the arm expression is a block.
This does, unfortunately, create the dangling else ambiguity. I'm not
sure this is much of a problem in practice, but it might be an issue.
The pretty printer would always omit the "then" and the "=>"/"," when
the alt arm is a block. That way, we aren't introducing multiple
preferred syntactic forms of the same Rust code (which I agree is
generally undesirable); the blessed style is to never over-annotate when
a "then" body or an alt expression is a block.
Here's an example piece of code (Jonanin's emulator) written
before-and-after:
Before: https://github.com/Jonanin/rust-dcpu16/blob/master/asm.rs
After: https://gist.github.com/2360838
Thoughts?
Patrick
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