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Let me get this straight: he's doing a a full circle -- without examining how the current situation came to be. At some point we went for exception, because (w

by dexen 15y ago

Let me get this straight: he's doing a a full circle -- without examining how the current situation came to be. At some point we went for exception, because (warning: big simplification ahead!) library authors figured they can't trust client code to always check return value for reported error condition. We got automatic, forced checking injected by compiler -- `exceptions'. With all the pains of fugly syntax in certain languages, because in many projects the trade-off makes sense. With the reasonable default for unexpected and unhandled condition: error is logged and process is stopped. Now the proposal -- `Let's have [[EDIT]]a tagged union: Either<error_code, return_value> ' takes us back to where we started -- client code is free to not check for errors. The process will not stop nor even print backtrace if the programmer forgets to check; the process will happily go on with invalid / unsupported / mangled / whatever data. No automatic propagation of error down the stack to outer handler in our function's caller. No stack unwind nor automatic object destruction. No hierarchy of error types (no specific errors derived from general ones). No nothing. And no discussion of those matters. Oh, my. Reliability in software has just gotten a new name. EDIT: fix'd mistake pointed out by tianyicui & thesz. Thanks!

tianyicui 15y ago
> Now the proposal -- `Let's have a tuple: Either<error_code, return_value> ' The Either data type is not a tuple.
- jerhewet 15y ago
  "In mathematics and computer science, a tuple is an ordered list of elements. [...] The term originated as an abstraction of the sequence: single, double, triple, quadruple, quintuple, sextuple, septuple, octuple, ..., n‑tuple, ..., where the prefixes are taken from the Latin names of the numerals. The unique 0‑tuple is called the null tuple. A 1‑tuple is called a singleton, a 2‑tuple is called a pair and a 3‑tuple is a triple or triplet." http://en.wikipedia.org/wiki/Tuple http://en.wikipedia.org/wiki/Tuple
  - thesz 15y ago
    "Either" isn't ordered list of elements. It's result of a choice, a tagged sum of sets. So Either is not a tuple by any mean.
    - Deestan 15y ago
      To elaborate: > "Either" isn't ordered list of elements. Although the Either<T,U> type looks like a pair definition, an Either<T,U> return value contains only one element of type T or U.
jerhewet 15y ago
> without examining how the current situation came to be. The problem, in a nutshell, with just about everything in the field of Computer Science today. See: George Santayana.
- dexen 15y ago
  Great pointer, thanks! I don't have problem with doing a full circle -- actually, that's a good thing once in a while. Cue Apple using BSD and GNU for MacOS X. I take issue with not considering what reasons got us where we are to-day, and what issues we bring back from the past. State of art (previous research and application work) should be laid out. Pros and cons have to be listed explicitly, or at least referenced. Weighted one against the other. I'd call that ``matter of scientific integrity'', if we were talking about Computer Science ;-)
tianyicui 15y ago
> [...] client code is free to not check for errors. The process will not stop nor even print backtrace if the programmer forgets to check; the process will happily go on with invalid / unsupported / mangled / whatever data. [...] This statement is simply not true, at least in languages that actually have Either data types (read: Haskell). But I'm not sure how to implement the generic class Either in Java.
- dexen 15y ago
  Please elaborate on how it works? Perhaps I got this very wrong; never used an Either<> class. Would an attempt to access the value (if an error was indicated instead) cause error condition? Would it be similar in nature to an exception?
  - masklinn 15y ago
    > Would an attempt to access the value (if an error was indicated instead) cause error condition? Would it be similar in nature to an exception? Either is a tagged union (actually a sum type), you have a value OR an error, which are typed (haskell uses Left and Right as the constructors for Either, by convention Left holds an error and Right holds a value, because right is correct). You can not just "cast" your Either, you have to type-check it with a case (or use monadic operators) to unwrap it, and with the right flag the compiler will ensure you're not missing cases. At compile time. Either is basically Schrödinger's box (the computation resulted in both a value and an error), and the compiler checks that you're set for handling both a dead and a live cat, or it will not let you open the box.
    - dexen 15y ago
      Thanks for explanations; now it makes sense to me. Another question: is there built-in support, or an idiom or standard practice for unwinding multiple levels of stack? Is it possible to have handler code is not directly in the function that called, but somewhere lower on the call stack -- and have it reached automatically like an exception does? Btw., it seems the bolder statement I post to HN, the wronger it turns out to be... oh, boy XD

by dexen 15y ago

tianyicui 15y ago

> Now the proposal -- `Let's have a tuple: Either<error_code, return_value> ' The Either data type is not a tuple.

jerhewet 15y ago
"In mathematics and computer science, a tuple is an ordered list of elements. [...] The term originated as an abstraction of the sequence: single, double, triple, quadruple, quintuple, sextuple, septuple, octuple, ..., n‑tuple, ..., where the prefixes are taken from the Latin names of the numerals. The unique 0‑tuple is called the null tuple. A 1‑tuple is called a singleton, a 2‑tuple is called a pair and a 3‑tuple is a triple or triplet." http://en.wikipedia.org/wiki/Tuple http://en.wikipedia.org/wiki/Tuple
- thesz 15y ago
  "Either" isn't ordered list of elements. It's result of a choice, a tagged sum of sets. So Either is not a tuple by any mean.
  - Deestan 15y ago
    To elaborate: > "Either" isn't ordered list of elements. Although the Either<T,U> type looks like a pair definition, an Either<T,U> return value contains only one element of type T or U.

jerhewet 15y ago

> without examining how the current situation came to be. The problem, in a nutshell, with just about everything in the field of Computer Science today. See: George Santayana.

dexen 15y ago
Great pointer, thanks! I don't have problem with doing a full circle -- actually, that's a good thing once in a while. Cue Apple using BSD and GNU for MacOS X. I take issue with not considering what reasons got us where we are to-day, and what issues we bring back from the past. State of art (previous research and application work) should be laid out. Pros and cons have to be listed explicitly, or at least referenced. Weighted one against the other. I'd call that ``matter of scientific integrity'', if we were talking about Computer Science ;-)

tianyicui 15y ago

> [...] client code is free to not check for errors. The process will not stop nor even print backtrace if the programmer forgets to check; the process will happily go on with invalid / unsupported / mangled / whatever data. [...] This statement is simply not true, at least in languages that actually have Either data types (read: Haskell). But I'm not sure how to implement the generic class Either in Java.

dexen 15y ago
Please elaborate on how it works? Perhaps I got this very wrong; never used an Either<> class. Would an attempt to access the value (if an error was indicated instead) cause error condition? Would it be similar in nature to an exception?
- masklinn 15y ago
  > Would an attempt to access the value (if an error was indicated instead) cause error condition? Would it be similar in nature to an exception? Either is a tagged union (actually a sum type), you have a value OR an error, which are typed (haskell uses Left and Right as the constructors for Either, by convention Left holds an error and Right holds a value, because right is correct). You can not just "cast" your Either, you have to type-check it with a case (or use monadic operators) to unwrap it, and with the right flag the compiler will ensure you're not missing cases. At compile time. Either is basically Schrödinger's box (the computation resulted in both a value and an error), and the compiler checks that you're set for handling both a dead and a live cat, or it will not let you open the box.
  - dexen 15y ago
    Thanks for explanations; now it makes sense to me. Another question: is there built-in support, or an idiom or standard practice for unwinding multiple levels of stack? Is it possible to have handler code is not directly in the function that called, but somewhere lower on the call stack -- and have it reached automatically like an exception does? Btw., it seems the bolder statement I post to HN, the wronger it turns out to be... oh, boy XD