[lkrubner]

The overall pattern of map-reduce is possible in most languages, certainly any language that has closures. And the idea of composing multiple reducing functions together is something that comes up in many languages. If a language does not have closures, you could do something similar in any language by walking an accumulating object through multiple loops, but that is awkward and ugly. But you could certainly do something like this in Javascript, through the clever use of multiple closures, composing the closures together. But transducers formalize this as an idiomatic part of Clojure.

[Tuna-Fish]

In languages with more leeway on execution order, this problem can be made to go away. For example, Haskell's stream fusion combines back-to-back calls to list processing functions into a single iteration over the list.

[seanmcdirmid]

Lazy evaluation can also be encoded fairly easily in strict languages using constructs like lazy stream abstractions.

[jeremyjh]

Uh, sure but does any other language have a compiler that actually implements stream fusion?

[gazarsgo]

Not in the compiler, but enjoy a Microsoft Research paper about Steno, a C# library that claims to be superior to stream fusion (section 8.2): http://research.microsoft.com/pubs/173946/paper-pldi.pdf

In case anyone is unaware, LINQ lets you represent queries as a series of function calls which it represents as a series of Expression objects and an in-memory AST.

[seanmcdirmid]

There is also the dynamic language run-time (DLR), which as a generalization of LINQ (to support statements) is pretty powerful when writing up these tools on .NET. I use it often in my work.

[DanWaterworth]

I don't believe GHC actually does implement stream fusion. I think stream fusion happens with rewrite rules.

[riffraff]

pardon my ignorance, but what would be the difference between the two? Don't rewrite rules happen in GCH anyway?

[DanWaterworth]

Sorry, I should have been clearer. The rewriting happens in GHC, but it's the application programmer who creates the rules. So, stream fusion isn't implemented by the compiler AFAIK.

[moomin]

The thing is, it's something of a redefinition of what idiomatic clojure is. Overloading arity to do radically different things isn't idiomatic Clojure, but transducers do it at two levels. Equally, functions are expected to do explicit state passing e.g. old school drop, rather than implicit state e.g transducer drop.