On 21/01/2012 18:08, Steve Horne wrote:
Even so, to see that strictness isn't the issue, imagine that (>>=) were rewritten using a unary executeActionAndExtractResult function. You could easily rewrite your lamba to contain this expression in place of x, without actually evaluating that executeActionAndExtractResult. You'd still be doing a form of composition of IO actions. And when you finally did force the evaluation of the complete composed expression, the ordering of side effects would still be preserved - provided you only used that function as an intermediate step in implementing (>>=) at least.
Doh!!! - that function *does* exist and is spelled "unsafePerformIO". But AFAIK it isn't used for compilation/interpretation of (>>=) operators. If it *were* used, the rewriting would also need an extra "return". So... a >>= b -> f b becomes... return (f (unsafePerformIO a))