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pcwalton's profile
Patrick Walton
Patrick Walton
Patrick Walton
@pcwalton

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Patrick Walton

@pcwalton

Research engineer at Mozilla

San Francisco, CA
pcwalton.github.io
Joined November 2009

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    1. Manish‏ @ManishEarth 11 Jan 2019
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      Replying to @pcwalton @rpjohnst @graydon_pub

      not really? they work almost like comments when it comes to parsing, except you tokenize their innards (unlike comments)

      1 reply 0 retweets 1 like
    2. Patrick Walton‏ @pcwalton 11 Jan 2019
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      Replying to @ManishEarth @rpjohnst @graydon_pub

      Of course they’re easy to *tokenize*, but they’re not easy to *expand*. Any tool that does not expand macros is broken.

      3 replies 1 retweet 3 likes
    3. Manish‏ @ManishEarth 11 Jan 2019
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      Replying to @pcwalton @rpjohnst @graydon_pub

      syntax highlighting parsers don't need to handle this :) nor does rustfmt but yes, I agree with your general point wrt proc macros

      2 replies 0 retweets 0 likes
    4. Patrick Walton‏ @pcwalton 11 Jan 2019
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      Replying to @ManishEarth @rpjohnst @graydon_pub

      Syntax highlighting doesn’t even need to parse the language, only lex it.

      2 replies 0 retweets 0 likes
    5. russell‏ @rpjohnst 11 Jan 2019
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      Replying to @pcwalton @ManishEarth @graydon_pub

      semantic highlighting needs to parse.

      1 reply 0 retweets 0 likes
    6. Patrick Walton‏ @pcwalton 11 Jan 2019
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      Replying to @rpjohnst @ManishEarth @graydon_pub

      Of all the difficulties involved in doing partial parses of Rust, with error recovery, etc, unbounded lookahead is not even in the top 100.

      1 reply 0 retweets 0 likes
    7. russell‏ @rpjohnst 11 Jan 2019
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      Replying to @pcwalton @ManishEarth @graydon_pub

      this isn't about some huge one-time insurmountable cost it's about drawing a line in the sand so the grammar doesn't slowly slide into something ugly

      1 reply 0 retweets 1 like
    8. Patrick Walton‏ @pcwalton 11 Jan 2019
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      Replying to @rpjohnst @ManishEarth @graydon_pub

      And I’m saying this is a pointless line to draw. Draw the line at, like, the lexer hack. Not this. If we had persisted with the “line in the sand” reasoning in Rust’s early days, we’d have been writing “match foo { None. => {…} }” because someone might name a variable None.

      1 reply 0 retweets 1 like
    9. Graydon Hoare‏ @graydon_pub 11 Jan 2019
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      Replying to @pcwalton @rpjohnst @ManishEarth

      Yes, that was a mistake.

      1 reply 0 retweets 5 likes
    10. Graydon Hoare‏ @graydon_pub 11 Jan 2019
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      Replying to @graydon_pub @pcwalton and

      It was compounded by dozens of other "just a little more" mistakes and we are now in 2019 and nobody even knows whether it'll be possible to formalize the language in a grammar at all.

      2 replies 0 retweets 5 likes
      Patrick Walton‏ @pcwalton 11 Jan 2019
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      Replying to @graydon_pub @rpjohnst @ManishEarth

      I don’t actually think it matters very much whether the language grammar can be formalized.

      5:16 PM - 11 Jan 2019
      1 reply 0 retweets 0 likes
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        2. Graydon Hoare‏ @graydon_pub 11 Jan 2019
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          Replying to @pcwalton @rpjohnst @ManishEarth

          I think it matters less than whether the type system or operational semantics can be formalized, but it's one of a number of areas of "treating the RI as canonical" that I think is not a great practice to reinforce.

          1 reply 0 retweets 2 likes
        3. Patrick Walton‏ @pcwalton 11 Jan 2019
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          Replying to @graydon_pub @rpjohnst @ManishEarth

          Being able to describe the grammar and being able to *formalize* it are different things. I agree that it’s good to be able to describe the grammar independently of implementation. I don’t care about formalisms for their own same.

          1 reply 0 retweets 0 likes
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