Hacker News Reader

Comment by Tuna-Fish | Hacker News Reader

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.

View on HN

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

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

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

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

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.

ah that makes sense, thanks.

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.

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.

Reply on news.ycombinator.com