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I'm trying to compare two completely arbitrary variables: the point is there's a dozen different ways where that comparison could involve type coercion. The "th

by ng12 9y ago

I'm trying to compare two completely arbitrary variables: the point is there's a dozen different ways where that comparison could involve type coercion. The "third boolean" value is useless unless you completely redesign the language.

lisper 9y ago
> I'm trying to compare two completely arbitrary variables But WHY are you trying to compare them? The fact that one of these variables is a field called LENGTH is highly suggestive of some particular semantics that you intend these variables to have. > there's a dozen different ways where that comparison could involve type coercion That's right, which is the reason I can't answer your question as you posed it. I predict that if you try to fill in the details what you will find is that you will be unable to do so in any way that does not reveal the presence of something badly wrong in your design. > The "third boolean" value is useless unless you completely redesign the language. You have to add an OTHERWISE clause to the IF statement and change the semantics of some operators. That's not a "complete redesign."
- nitrogen 9y ago
  It sounds like OTHERWISE is vaguely analogous to a catch on Java's ClassCastException (assuming it would be thrown for any nonsensical comparison). Traditonal if/else maps IF to true and ELSE to false|undefined; OTHERWISE simply extracts the undefined case to a separate clause. Interesting way of expressing the result of an ill-defined operation. Or am I off base?
  - lisper 9y ago
    No, you're exactly right. If you think about it, both of these things are (almost) exactly equivalent. In both cases you are separating out a third control branch. The only difference is the syntax you use to specify what happens on that third branch, and whether or not that branch is taken immediately when the non-true-non-false value is generated. It is exactly the difference between (say)dividing by zero throwing an exception or returning an infinity or a NaN.
  - catnaroek 9y ago
    Exceptions are very much well-defined results. They just aren't the result you were originally expecting. But the meaning of a program is defined in terms of the language's own semantics, not what the programmer expects.
- deleted 9y ago
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by ng12 9y ago

lisper 9y ago

> I'm trying to compare two completely arbitrary variables But WHY are you trying to compare them? The fact that one of these variables is a field called LENGTH is highly suggestive of some particular semantics that you intend these variables to have. > there's a dozen different ways where that comparison could involve type coercion That's right, which is the reason I can't answer your question as you posed it. I predict that if you try to fill in the details what you will find is that you will be unable to do so in any way that does not reveal the presence of something badly wrong in your design. > The "third boolean" value is useless unless you completely redesign the language. You have to add an OTHERWISE clause to the IF statement and change the semantics of some operators. That's not a "complete redesign."

nitrogen 9y ago
It sounds like OTHERWISE is vaguely analogous to a catch on Java's ClassCastException (assuming it would be thrown for any nonsensical comparison). Traditonal if/else maps IF to true and ELSE to false|undefined; OTHERWISE simply extracts the undefined case to a separate clause. Interesting way of expressing the result of an ill-defined operation. Or am I off base?
- lisper 9y ago
  No, you're exactly right. If you think about it, both of these things are (almost) exactly equivalent. In both cases you are separating out a third control branch. The only difference is the syntax you use to specify what happens on that third branch, and whether or not that branch is taken immediately when the non-true-non-false value is generated. It is exactly the difference between (say)dividing by zero throwing an exception or returning an infinity or a NaN.
- catnaroek 9y ago
  Exceptions are very much well-defined results. They just aren't the result you were originally expecting. But the meaning of a program is defined in terms of the language's own semantics, not what the programmer expects.
deleted 9y ago
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