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POIs non-local type inference in Haskell or OCaml really useful?
 

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  1. POIs non-local type inference in Haskell or OCaml really useful?
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    <p>First, let us assume that local type inference is the sort of type inference found in Scala and C#. Scala local type inference is explained here: <a href="http://www.scala-lang.org/node/127" rel="nofollow">http://www.scala-lang.org/node/127</a> </p> <p>Also, let us assume, that a definition such as</p> <pre><code> fact 0 = 1 fact n = n * fact(n-1) </code></pre> <p>would count as local type inference -- that is, type inference here is local to function fact. Scala does not permit such a type inferece; still let us count it as local.</p> <p>The question, then, is whether anyone has a practical example of at least 2 mutually-recursive functions (or any other non-locality at your discretion) that derive some benefit from type inference? Please do not post silly examples such as:</p> <pre><code> odd 0 = false odd n = even(n-1) even 0 = true even n = odd(n-1) </code></pre> <p>I suspect that non-silly, practical examples arise in parses. Also, please could you explain the benefits a programmer could derive from such uses of non-local type inference?</p> <p>UPDATE:</p> <p>I appreciate any example of insufficiency of local type inference and the need for full-blown type inference.</p> <ol> <li><p>Your Haskell or OCaml example may be 90% correct, because you are only 90% understand the term "non-local type inference". Still, you have to understand Haskell (or OCaml) type inference. </p></li> <li><p>Your example may be written on Scala or C#. Please point out that compliler really has enough information to infer the type, but the type can not be inferred due to language specification or due to local-only nature of type inference in Scala or C#.</p></li> </ol> <p>// And again, feel free to correct my english.</p>
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    1. USMartijn Pieters
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    1. COI am often annoyed by the _local-only_ nature of type inference in C#. For example, if I want to refactor a LINQ query into a function, I am often obligated to do a bunch of incidental coding (such as coming up with a one-off type to represent the query projection) to make that happen.
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      1. USDaniel Pratt
    2. CO@DanielPratt could you give a more detailed example of such a situation? may be post a link to your blog article; I am interested in type inference in any language
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    3. COThis seems like an odd question. The benefits are the same as any other type inference, and having *only* local inference is a spurious limitation that gets in the way of refactoring, as Daniel Pratt says. Why do you need a specific example for "why to not cripple a useful feature"?
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      1. USC. A. McCann
 

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