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Many CL implementations have a type inferencer (usually so that the compiler can optimize code without the developer having to specify types everywhere). What s
by lispm 8y ago
Many CL implementations have a type inferencer (usually so that the compiler can optimize code without the developer having to specify types everywhere). What sets SBCL (and CMUCL and Scieneer CL) apart is that it does limited forms of compile time type checking:
http://www.sbcl.org/manual/index.html#Handling-of-Types http://www.sbcl.org/manual/index.html#Handling-of-Types
- lisper 8y ago> type inferencer > compile time type checking Aren't those the same thing?
- omaranto 8y agoI don't think so. A type inferencer figures out types of expressions that don't have a type explicitly declared using information it has about other things that are declared. A compile time type checker is expected to signal errors at compile time for programs whose types don't check out. You can use a type inferencer without signaling any errors at compile time (for example, by deferring errors to runtime) and you can signal type errors at compile time even if you don't infer any types (like C compilers, that demand all variables have a declared type).
- lispm 8y agoNo. A type inference does not check types. It inferences types. For example if you know that + is defined for numbers, then you can inference that a and b must be numbers: (+ a b) If you know that a and b are numbers then you can inference that subexpressions need to deal with numbers only: (let ((a c) (b d)) (declare (type number a b)) ....) The type inferencer then will tell what types the various expressions have. It will try to propagate known types as widely as possible in the code. Allegro CL and LispWorks for example are doing this type inference. But their compiler will not tell you that type declarations are violated. SBCL OTOH treats type declarations as type assertions which can be checked at compile time. ADDITIONALLY it also does type inference - and additionally uses this information for compile time type checks.
- JasonFruit 8y ago('Infer' is a perfectly good verb; you don't have to make one out of 'inference'. But sometimes it's easy to disremembrance things like that on HN.)
- lisper 8y agoI believe lispm is not a native English speaker. His website TLD is .de.
- JasonFruit 8y agoYes, I see. Doesn't mean he or she might not rather be correct, however.
- lisper 8y agoTrue that.
- deleted 8y ago[deleted]
- lispm 8y agoThanks, didn't remember that.
- mercer 8y agoIt's an easy mistake to make. Incidentally, "infer", for some reason, is a word I find unusually pleasing. EDIT: as a non-native speaker I distinctly remember first reading the word and happily using it ever since, when appropriate.
- JasonFruit 8y agoPerfectly fair — I'm sure you're not the first to inference something. And yes, 'infer' is an interesting word, especially when you bring in Latin.