I understand that there will be issues integrating with Java, but I want to consider a Haskell solution nevertheless. Are monadic programming concepts essential to create a DSL. I am just learning Haskell and haven't grasped fully the concepts of monadic programming yet. Referring to Paul's paper "Modular Domain Specific Languages", it seems like a DSEL in Haskell is just a plain Haskell program that uses functions to model the business domain. I am referring to the DSEL for gemoetric region analysis and Fran both of which look like code in familiar Haskell syntax. Our business problem is in the financial space where we have rules that check compliance on portfolios. Some example rules are: - The portfolio may not invest more than 40% in equity securities. - The portfolio may not invest more than 5% in any sector relative to the S&P500 index. - The portfolio cannot buy any securities whose issuers are domiciled in Japan. Currently we have high level rule expressions that get mapped to low-level code that embodies the business logic of checking the rules. Essentially most of our rules do the following: 1. Group, sort, and filter the portfolio's holdings. 2. Examine individual groups (also called 'buckets') and compute aggregated values. Eg. percent market value of each bucket. 3. Compare the value for each group with threshold values to check compliance I am wondering if is is a good idea to express the above logic in a Haskell DSL by creating data types for Holding, Bucket, Portfolio, etc. Would I be going on the right track by modelling a concentration rule as: -- A concentration rule takes a list of Holdings and a list -- of filter rules and returns an aggregate number. conc :: [Holding] -> [holdingFilter] -> Float holdingFilter :: Holding -> Boolean -- Shoeb -----Original Message----- From: Paul Hudak [mailto:paul.hudak@yale.edu] Subject: Re: [Haskell-cafe] Integrating Haskell into a J2EE environment 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

...

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