However, I'm a Java pro, and there are many technical issues on the Java side that scream at me to keep out of the native arena, especially in a J2EE container environment, where funny things can happen with hot reloads (dumping old ClassLoaders for new ones), clustering, and the like.
So it wasn't out of denigration of Haskell that I made my recommendation; far from it...from what I've seen Haskell is perfect for implementing DSL's. Rather, from the Java side is where it becomes problematic. There have been many problems integrating with native libraries from within a J2EE container, and I try to seek the most cost-effective way (I'm an independent consultant) to get the problem solved for my customers.
--doug
On Oct 6, 2004, at 2:59 PM, Paul Hudak wrote:
I wouldn't write off Haskell so quickly. All of what Shoeb describes concerning DSL issues might be much more easily solved in Haskell, and will certainly be more flexible than a hard-wired approach. The J2EE interface might be ugly, but if the functionality needed is not too great it might not be too bad. Generally speaking, these kinds of apps -- in this case "a DSL for high-level business rules" -- sounds like just the sort of thing that Haskell is good for.
-Paul
Doug Kirk wrote:
You're going to spend alot of time marshalling between Java and Haskell values, and you'll either have to do it via JNI or by using pipes [as in System.exec("haskellprogram param param param")], both of which are ugly for a Java app.
Have you looked at Jython and JRuby? Jython is an implementation of a Python interpreter in 100% Java, and JRuby implements a Ruby interpreter in 100% Java.
Those might get the job done faster than having to delve into the native layer. (Not to mention learning how to use Haskell in order to implement what you want--not a trivial task in itself!)
Take care,
--doug
On Oct 5, 2004, at 4:33 PM, Bhinderwala, Shoeb wrote:
Hi All,
I am new to Haskell and this mailing list.
We have a system that uses a custom high-level language to express
high-level business rules. Expressions in the high-level language get
compiled to Java bytecode. We express the grammar using BNF notation as
required by the javacc parser tool. This is then converted to an AST
using jjtree and from there we build the final Java code. Our language
could be considered a domain-specific language (DSL) and is used by our
business users to express very high-level business logic. The language
currently is very limited - we support boolean logic, function
invocations and if-then statements. We want to convert it into a more
powerful scripting language so that even lower level business logic can
be expressed in it.
I came across a few papers that talk about writing a DSL with Haskell as
the underlying support language. How is this done. Is it possible to
create a sort of domain specific business scripting language easily. How
does that then compile to Haskell code. And how can the Haskell code be
invoked from Java.
Essentially, I am thinking if I could use a Haskell like DSL language to
express our business rule logic and then be able to integrate into and
invoke the logic from a J2EE app server environment. Has anybody done
anything like this with Haskell.
-- Shoeb
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