4 ms·

> Not sure about Rust Rust has made a point of being parser-friendly, to support tooling. The entire reason the turbofish ::<> exists is to avoid ambiguous gra

by lmkg 7y ago

> Not sure about Rust Rust has made a point of being parser-friendly, to support tooling. The entire reason the turbofish ::<> exists is to avoid ambiguous grammar. (This operator seems to vex people, I don't get the hate.)

estebank 7y ago
Do note that Rust the language is regular and easy to parse, but rustc the compiler actually performs bounded lookahead and contextual parsing on parse errors to detect common typos and invalid syntax that would otherwise be vexing to users. The nightly only type ascription : syntax is a good example because it crops up in several different contexts as a 1-substitution typo and used to be terrible (may it burn in a fire). The turbofish is another case where we now suggest the correct syntax, but there are many, many more.
- usrusr 7y ago
  Surely that's an example of how parser-friendly syntax empowers tooling? I imagine that it would be much harder to guess intention and fixes from lookahead and context if those were already necessary to make sense of correct code?
WalterBright 7y ago
Being parser-friendly is not at all the same thing as being user-friendly. The difficulty of writing parsers is way overblown. One thing to avoid is depending on the existence of the symbol table to parse correctly. (C++ has this problem.) Needing a symbol table makes it hard for parsers like source code formatting and syntax highlighting. Another is to avoid raw string literals that reach back and try to unwind the results of previous "phases of translation".
- barrkel 7y ago
  Agree with a caveat; if the syntax has many ambiguities, with resolution solved by a clever parser, it'll be confusing for users, especially newbies, because they'll tend to get errors unrelated to what they were trying to achive. Redundancy in syntax can be a bonus.
  - WalterBright 7y ago
    > Redundancy in syntax can be a bonus. I agree. I even wrote an article about that: https://www.digitalmars.com/articles/b05.html https://www.digitalmars.com/articles/b05.html
- seanmcdirmid 7y ago
  Both humans and computers parse code. Humans can handle ambiguity mode easily than computers, but that doesn’t make the ambiguity more user friendly somehow.
thrtythreeforty 7y ago
I love the turbofish so much, not because it looks nice in code or anything, but because the name is a bit of harmless fun that makes the language feel inviting.

by lmkg 7y ago

estebank 7y ago

Do note that Rust the language is regular and easy to parse, but rustc the compiler actually performs bounded lookahead and contextual parsing on parse errors to detect common typos and invalid syntax that would otherwise be vexing to users. The nightly only type ascription : syntax is a good example because it crops up in several different contexts as a 1-substitution typo and used to be terrible (may it burn in a fire). The turbofish is another case where we now suggest the correct syntax, but there are many, many more.

usrusr 7y ago
Surely that's an example of how parser-friendly syntax empowers tooling? I imagine that it would be much harder to guess intention and fixes from lookahead and context if those were already necessary to make sense of correct code?

WalterBright 7y ago

Being parser-friendly is not at all the same thing as being user-friendly. The difficulty of writing parsers is way overblown. One thing to avoid is depending on the existence of the symbol table to parse correctly. (C++ has this problem.) Needing a symbol table makes it hard for parsers like source code formatting and syntax highlighting. Another is to avoid raw string literals that reach back and try to unwind the results of previous "phases of translation".

barrkel 7y ago
Agree with a caveat; if the syntax has many ambiguities, with resolution solved by a clever parser, it'll be confusing for users, especially newbies, because they'll tend to get errors unrelated to what they were trying to achive. Redundancy in syntax can be a bonus.
- WalterBright 7y ago
  > Redundancy in syntax can be a bonus. I agree. I even wrote an article about that: https://www.digitalmars.com/articles/b05.html https://www.digitalmars.com/articles/b05.html
seanmcdirmid 7y ago
Both humans and computers parse code. Humans can handle ambiguity mode easily than computers, but that doesn’t make the ambiguity more user friendly somehow.

thrtythreeforty 7y ago

I love the turbofish so much, not because it looks nice in code or anything, but because the name is a bit of harmless fun that makes the language feel inviting.