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edwinbrady's profile
Edwin Brady
Edwin Brady
Edwin Brady
@edwinbrady

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Edwin Brady

@edwinbrady

CompSci Lecturer. Go player. Programming language researcher. Idris hacker. Denies knowledge of Whitespace. He/him. http://tinyurl.com/TypeDD 

St Andrews
eb.host.cs.st-andrews.ac.uk
Joined November 2008

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    1. Edwin Brady‏ @edwinbrady 12 Jan 2018
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      As understanding of a problem develops, types get refined to better explain what's going on. Not necessarily bigger, just better. We're going to need much better editing and refactoring tools than we currently have, though, to do this well.

      3 replies 5 retweets 38 likes
      Show this thread
    2. Ron Pressler‏ @pressron 14 Jan 2018
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      Replying to @edwinbrady

      But why should you express your understanding _in types_? Ultimately you'll get to the point that ties specification to proof. What if your understanding is hard to prove but easy to verify (well enough)? Limiting "understanding" to formal provability seems wrong for programming.

      1 reply 1 retweet 9 likes
    3. Edwin Brady‏ @edwinbrady 20 Jan 2018
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      Replying to @pressron

      Who said anything about “limiting”? I find it helps me understand things. Using types doesn’t rule out using other methods.

      1 reply 1 retweet 4 likes
    4. Edwin Brady‏ @edwinbrady 20 Jan 2018
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      Replying to @edwinbrady @pressron

      Sometimes I also find it useful to state properties as types but leave them as axioms. It’s up to the programmer to decide when to stop.

      1 reply 0 retweets 3 likes
    5. Ron Pressler‏ @pressron 20 Jan 2018
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      Replying to @edwinbrady

      Proofs and axioms are far from the only ways to use propositions. In fact, when it comes to programs (rather than math), I would say that they are the two worst ways. One promises everything yet provides little, and the other is too costly and provides too much (usually).

      2 replies 0 retweets 3 likes
    6. Boltzmann Brain Think Tank‏ @PLT_cheater 21 Jan 2018
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      Replying to @pressron @edwinbrady

      What would you say are the top best ways?

      1 reply 0 retweets 0 likes
    7. Ron Pressler‏ @pressron 22 Jan 2018
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      Replying to @PLT_cheater @edwinbrady

      Fully automated, though weaker ways: static analysis/automated proof of weakened properties, model checking (possibly of finite instance), concolic tests (generated from spec), randomized tests (generated from spec), assertions (generated from spec).

      1 reply 0 retweets 1 like
    8. Ron Pressler‏ @pressron 22 Jan 2018
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      Replying to @pressron @PLT_cheater @edwinbrady

      By weakened properties for I mean a spec that says that the output must be prime, and the tool says, well, I can’t automatically prove primality, but I can automatically prove the number is odd. You can then automatically generate tests/assertions for primality.

      1 reply 0 retweets 1 like
    9. Boltzmann Brain Think Tank‏ @PLT_cheater 22 Jan 2018
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      Replying to @pressron @edwinbrady

      I was going to ask!

      1 reply 0 retweets 0 likes
    10. Ron Pressler‏ @pressron 22 Jan 2018
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      Replying to @PLT_cheater @edwinbrady

      The first rule of software specification is that the precision of the spec should not be related to the means/strength of verification. The spec should be precise, but you can choose to prove a weaker property and/or use weaker verification.

      1 reply 0 retweets 1 like
      Edwin Brady‏ @edwinbrady 22 Jan 2018
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      Replying to @pressron @PLT_cheater

      The whole point of my thread was that dependent types are about much more than specification, and discussions always assume otherwise.

      5:56 AM - 22 Jan 2018
      1 reply 0 retweets 0 likes
        1. New conversation
        2. Ron Pressler‏ @pressron 22 Jan 2018
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          Replying to @edwinbrady @PLT_cheater

          Alright, but that’s what I’m having a hard time understanding. What’s the difference between “expressing your understanding” and writing an invariant? And your linking of “specification and proof” confused me further because in formal methods we (try to) separate the two.

          1 reply 0 retweets 0 likes
        3. Edwin Brady‏ @edwinbrady 22 Jan 2018
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          Replying to @pressron @PLT_cheater

          Fair enough. I can see we’re never going to agree here, so I’m going to do productive things. I hope all our favoured methods work out!

          1 reply 0 retweets 1 like
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