This should be possible using higher-order terms, as in http://hackage.haskell.org/packages/archive/compdata/latest/doc/html/Data-Co... The only complication I see is that the Dag nodes would get heterogeneous types requiring existential quantification with a `Typeable` constraint. A better representation might be typed ASGs [1] Syntactic has typed ASTs and it has a module that does something similar to data-fix-cse (uses a combination of stable names and hashing), but it needs some fixing up. / Emil [1]: http://dl.acm.org/citation.cfm?id=2426909 2013-02-20 01:58, Conal Elliott skrev:
Do you think the approach can be extended for non-regular (nested) algebraic types (where the recursive data type is sometimes at a different type instance)? For instance, it's very handy to use GADTs to capture embedded language types in host language (Haskell) types, which leads to non-regularity.