Re: [Haskell-cafe] I love purity, but it's killing me.

On Fri, 8 Feb 2008, Tom Hawkins wrote:

5) Forget embedding the DSL, and write a direct compiler.

In addition to the sharing problem, another shortcoming of Haskell DSLs is they can not fully exploit the benefits of algebraic datatypes. Specifically, pattern matching ADTs can only be used to control the compile-time configuration of the target, it can't be used to describe the target's behavior -- at least for DSLs that generate code that executes outside of Haskell's runtime.

Also in a pure Haskell library you will try to avoid direct access to constructors, because the internal data structures might change. Better are functions that access the internal data of a type, like 'maybe' and 'either' for 'Maybe' and 'Either', respectively.