Lazy big-O and Haskell Answers

September 3rd, 2006

First, Evan has a host of interesting articles about Haskell, and I found his lazy big-O article particulary interesting.

Next, Eric Warmenhoven has recently taken up Haskell and posted some Haskell questions on his blog. Eric, here are some answers for you.

First, regarding shared libraries. While Haskell can be compiled to machine code, and GHC is a popular way to do that, a standard C way of representing information about a library (.h and .so files) is not really rich enough for Haskell. Consider, for instance, that functions may accept arguments of a wide range of types (or even things such as lists of any type). Haskell also performs type checking, and thus must know the type of arguments a function expects, as well as its return type, at compile time. So you do not generally compile Haskell code directly to .so files, but rather use the compiler’s module or package support to do that. See Cabal for more information on packages. Through the FFI (Foreign Function Interface), it is possible to both call into C and be called from C with Haskell code, if that’s where you want to go. It is actually easier in Haskell than in any other high-level language I’ve dealt with before.

Regarding circular module deps — I’ve never used them and can’t really comment. I can say, though, that the .boot files are internal files created by GHC.

Regarding practical stuff in tutorials — I share your complaint there. I have found a few that are better than the others: Yet Another Haskell Tutorial, and Haskell: The Craft of Functional Programming, 2nd ed., by Simon Thompson. Several of us are working intermittently on a project called Haskell V8 — take a look and darcs send me patches! I would say that Haskell’s I/O system is the most powerful I’ve seen in many ways — especially with regard to laziness — and in the upcoming GHC 6.6 release, it will be both lazy *and* blazingly fast. Very nice.

There isn’t much Debian-specific documentation, but there is a draft policy and a mailing list (link to it is in the policy doc).

Hope this helps!

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