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> except that I'm not sure how different it is from mine, because the equational law you refer to applies to syntactic terms An effectful language can be given

> except that I'm not sure how different it is from mine, because the equational law you refer to applies to syntactic terms An effectful language can be given a denotational semantics. At least from what I've seen, when most people say “pure”, they mean “effect-free”. > It's easy to come with an equivalence relation that would hold for `foo`, but not at the syntax level [emphasis mine] Yep, indeed, that's the whole point.

pron 10y ago
> when most people say “pure”, they mean “effect-free” But saying "effect free" doesn't mean much unless you define what an effect is, and what constitutes an effect depends on the language. I meant to define the same thing without referring to another vague definition.
- catnaroek 10y ago
  I already defined above what an effect is. My definicion is technically precise and language-independent.
  - pron 10y ago
    OK, so you define effect-freedom using the language's equality operator. I agree it's a better definition than mine, but I think assembly language and BASIC would still qualify as effect-free (provided there's no concurrency) even though some people would not consider them pure.
    - catnaroek 10y ago
      > OK, so you define effect-freedom using the language's equality operator. Not the runtime equality testing operator. Rather, the language's static notion of contextual equivalence. It just happens to be the case that most high-level languages provide a built-in equality testing operator that works on primitive types, returning `true` iff its operands are contextually equivalent values. > I think assembly language and BASIC would still qualify as effect-free I don't even know what a good notion of contextual equivalence for any assembly language would be. As for BASIC, I haven't used the old ones, so I can't comment on them. I've used Visual Basic, which most certainly has effectful procedures.
      - pron 10y ago
        > Not the runtime equality testing operator. Rather, the language's static notion of contextual equivalence. How is that different from denotational semantics? > The ones that can be effectful or effect-free are specific computations, not whole languages. Well, we could define an effect-free language as one where all programs are effect-free. But anyway, what is the "static notion of contextual equivalence" in assembly (or BASIC), and how can you write an effectful program in such a language?

pron 10y ago

> when most people say “pure”, they mean “effect-free” But saying "effect free" doesn't mean much unless you define what an effect is, and what constitutes an effect depends on the language. I meant to define the same thing without referring to another vague definition.

catnaroek 10y ago
I already defined above what an effect is. My definicion is technically precise and language-independent.
- pron 10y ago
  OK, so you define effect-freedom using the language's equality operator. I agree it's a better definition than mine, but I think assembly language and BASIC would still qualify as effect-free (provided there's no concurrency) even though some people would not consider them pure.
  - catnaroek 10y ago
    > OK, so you define effect-freedom using the language's equality operator. Not the runtime equality testing operator. Rather, the language's static notion of contextual equivalence. It just happens to be the case that most high-level languages provide a built-in equality testing operator that works on primitive types, returning `true` iff its operands are contextually equivalent values. > I think assembly language and BASIC would still qualify as effect-free I don't even know what a good notion of contextual equivalence for any assembly language would be. As for BASIC, I haven't used the old ones, so I can't comment on them. I've used Visual Basic, which most certainly has effectful procedures.
    - pron 10y ago
      > Not the runtime equality testing operator. Rather, the language's static notion of contextual equivalence. How is that different from denotational semantics? > The ones that can be effectful or effect-free are specific computations, not whole languages. Well, we could define an effect-free language as one where all programs are effect-free. But anyway, what is the "static notion of contextual equivalence" in assembly (or BASIC), and how can you write an effectful program in such a language?