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If 3-value logic is such a good idea, why doesn't any modern general-purpose language use it? And even if it were a good idea, leaving the user with no built-i

by Pxtl 5y ago

If 3-value logic is such a good idea, why doesn't any modern general-purpose language use it? And even if it were a good idea, leaving the user with no built-in operators, not even a simple COALESCE(bool) to properly manage the null complexity? That's unacceptable. Given a SQL boolean expression `f(b)` that can return true, false, or null, how do I test if `f(b)` has returned NULL? How do I handle that NULL case? ANSI SQL gives users a strange new paradigm for boolean algebra and then says "GLHF" and gives you zero tools to handle the situation, not even linguistic features that would let you roll your own boolean-based functions, since you can't write SVFs that take boolean parameters. I mean this trashboat of a language doesn't even let you bind boolean to a variable! You have to deal with the PITA of converting from Booleans to bits because those are totally different things.

civilized 5y ago
Because you can implement 3-valued logic using boolean logic in a general-purpose programming language if you need it, and most applications don't benefit from the extra nuance and complexity. But data management sure does, as I illustrated in my post with the color example. Notice that databases, with their 3-valued logic, are written in a systems language like C/C++, a general-purpose programming language with boolean logic. Some systems are best thought of using non-boolean logic. Quantum systems are another example. You can simulate just about anything with a Turing-complete language, but it doesn't mean that standard computation with boolean logic is the best way to think about every domain.
- Pxtl 5y ago
  > Because you can implement 3-valued logic using boolean logic in a general-purpose programming language if you need it, and most applications don't benefit from the extra nuance and complexity. Surely if it were beneficial you'd see more people doing it, but I have literally never encountered software outside of SQL that does it. I could probably implement it in C++ or C# in an afternoon using enums and operator overloading, at least for the boolean-boolean operators. A little longer to make comparison operators for the other basic types that would yield nulls when compared to null. But nobody does this. Why?
  - civilized 5y ago
    > Surely if it were beneficial you'd see more people doing it, but I have literally never encountered software outside of SQL that does it. Do you see SQL as some weird little edge case of data management? 99.9% of all serious data management happens in a database server with a SQL interface. Maybe other languages don't implement 3-valued logic because they don't need it, because they don't need to do data management, because they'd be bad at data management. It's not even true that languages outside SQL don't have 3-valued logic. They may not have it built into the base language, but analytics packages like Python/pandas and R certainly have some version of a null or NA, and nobody would question the value of it for a second. And databases are typically implemented using C/C++, so there's another example of someone using a general-purpose programming language to implement 3-valued logic (as part of the SQL implementation that is written in C/C++). It's not like SQL is some weird separate language on a different planet as your favorite general purpose programming languages. It's implemented with those languages. So there's your 3-valued implementation right there. When the feature is valuable, it's implemented, and not before.
matwood 5y ago
> If 3-value logic is such a good idea, why doesn't any modern general-purpose language use it? Many languages have a null/undefined of some sort, but they are often simply coerced to false. But, for a language whose sole purpose is to manipulate data the null value nearly always has meaning. > Given a SQL boolean expression `f(b)` that can return true, false, or null, how do I test if `f(b)` has returned NULL? How do I handle that NULL case? http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt Section 8.6, the null predicate. `where f(b) is null` > ANSI SQL gives users a strange new paradigm for boolean algebra and then says "GLHF" and gives you zero tools to handle the situation. It's also not a strange new paradigm, and is in fact built on foundational topics. Relational algebra and set theory are not new concepts.
- Pxtl 5y ago
  The term 3-value logic pretty obviously implies the behavior of operators as they relate to NULL, not just the fact that data is nullable, of course. AFAIK MySQL, Oracle, and SQL Server don't have the Boolean datatype as a variable/column type - only Bit, which lacks boolean semnatics, and so Booleans are not considered data values, and therefore can't be used with IS NULL or COALESCE.

by Pxtl 5y ago

civilized 5y ago

Because you can implement 3-valued logic using boolean logic in a general-purpose programming language if you need it, and most applications don't benefit from the extra nuance and complexity. But data management sure does, as I illustrated in my post with the color example. Notice that databases, with their 3-valued logic, are written in a systems language like C/C++, a general-purpose programming language with boolean logic. Some systems are best thought of using non-boolean logic. Quantum systems are another example. You can simulate just about anything with a Turing-complete language, but it doesn't mean that standard computation with boolean logic is the best way to think about every domain.

Pxtl 5y ago
> Because you can implement 3-valued logic using boolean logic in a general-purpose programming language if you need it, and most applications don't benefit from the extra nuance and complexity. Surely if it were beneficial you'd see more people doing it, but I have literally never encountered software outside of SQL that does it. I could probably implement it in C++ or C# in an afternoon using enums and operator overloading, at least for the boolean-boolean operators. A little longer to make comparison operators for the other basic types that would yield nulls when compared to null. But nobody does this. Why?
- civilized 5y ago
  > Surely if it were beneficial you'd see more people doing it, but I have literally never encountered software outside of SQL that does it. Do you see SQL as some weird little edge case of data management? 99.9% of all serious data management happens in a database server with a SQL interface. Maybe other languages don't implement 3-valued logic because they don't need it, because they don't need to do data management, because they'd be bad at data management. It's not even true that languages outside SQL don't have 3-valued logic. They may not have it built into the base language, but analytics packages like Python/pandas and R certainly have some version of a null or NA, and nobody would question the value of it for a second. And databases are typically implemented using C/C++, so there's another example of someone using a general-purpose programming language to implement 3-valued logic (as part of the SQL implementation that is written in C/C++). It's not like SQL is some weird separate language on a different planet as your favorite general purpose programming languages. It's implemented with those languages. So there's your 3-valued implementation right there. When the feature is valuable, it's implemented, and not before.

matwood 5y ago

> If 3-value logic is such a good idea, why doesn't any modern general-purpose language use it? Many languages have a null/undefined of some sort, but they are often simply coerced to false. But, for a language whose sole purpose is to manipulate data the null value nearly always has meaning. > Given a SQL boolean expression `f(b)` that can return true, false, or null, how do I test if `f(b)` has returned NULL? How do I handle that NULL case? http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt Section 8.6, the null predicate. `where f(b) is null` > ANSI SQL gives users a strange new paradigm for boolean algebra and then says "GLHF" and gives you zero tools to handle the situation. It's also not a strange new paradigm, and is in fact built on foundational topics. Relational algebra and set theory are not new concepts.

Pxtl 5y ago
The term 3-value logic pretty obviously implies the behavior of operators as they relate to NULL, not just the fact that data is nullable, of course. AFAIK MySQL, Oracle, and SQL Server don't have the Boolean datatype as a variable/column type - only Bit, which lacks boolean semnatics, and so Booleans are not considered data values, and therefore can't be used with IS NULL or COALESCE.