I've just uploaded a new version of syntactic: http://hackage.haskell.org/package/syntactic The most important change is that I've added observable sharing based on StableNames. The implementation and interface are conceptually quite similar to Andy Gill's data-reify. The library offers both referentially transparent common sub-expression elimination (that uses a combination of hashing and observable sharing under the hood), as well as direct observation of sharing. The difference between the two flavors is demonstrated in the accompanied file: Examples/NanoFeldspar/Test.hs (See test7_X.) Still missing a way to rebuild an expression with let bindings from the syntax graphs. This is ongoing work. / Emil