The functional programming language community seems to be moderately abuzz over the recent release of the Disciplined Disciple Compiler. The first announcement I saw for it I ignored almost completely. Dialect of Haskell, allows destructive updates, allows mixing lazy and strict, etc. None of that really grabbed me.

Then this afternoon I saw another blog mentioned it on the Planet Haskell feed. This time it was mentioned with the phrase “region, effect, and closure inference” and immediately I had to read more about it.

The compiler seems to be a Google summer of code project by an Australian Ph.D. student. There is no paper yet! This means trying to figure out what’s going on involves combing through all the wiki pages and reading some tea leaves. Regions—à la Tofte—are not used for memory allocation. Darn! They seem to be used as part of the effect system, e.g., to mark certain regions of memory as being pure/constant/read-only or allowing destructive updates.

All of the magic is in the type system. It looks very well thought-out and very rich and is all orthogonal to the usual Haskell type system.

It looks like an interesting language to follow. I shall be keeping track of its developments.

From a syntactic stand-point, it seems to further my belief that you need to choose a “side” on the strict versus lazy issue. Disciple should in theory nicely and transparently mix strictly evaluated expressions with lazily evaluated ones. In practice this means things are strict by default but can be made lazy with annotations.

In my mind, what defines a language as being “strict” or “lazy” is the standard library. A language which truly is agnostic on the issue should allow, for example, map to be used in either a strict or lazy manner rather than having both a strict map and a lazy map. I don’t see an easy way to get this, so for the time being it seems languages have to pick sides.

In a similar vein, one of the nice features of Disciple is that its effect system ends the duality in Haskell between pure and impure functions. For instance, in Haskell you have a map which works on pure functions and a mapM which works on monadic functions. No such division exists in Disciple.

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