| I remember once reading a paper by SPJ about Optimistic Evaluation that | is somewhere between lazy and strict. If I remember correctly, they even | implemented it in GHC. Now, it seems that current version of GHC doesn't | support optimistic evaluation (not even as an optional feature), so my question | is: what happened to OE? Was it that it seemed like a good idea on paper | but not in reality? Or was it too costly to maintain? Or it didn't deliver | the goods it promised? I'm just curious. It was great stuff -- and some lazy programs went a lot faster -- but it was also jolly complicated when all the details were worked out, and interacted with a lot of other tricky details of the run-time system. In the end we decided it was just too complicated to permanently incorporate in GHC's code base, alas. You can find the paper, along with Rob's thesis (which gives a lot more detail) here: http://research.microsoft.com/%7Esimonpj/Papers/optimistic/index.htm (Well, the thesis should appear there shortly; if not, look on Rob's web page.) Simon