Why is F#'s type inference so fickle?

Question

The F# compiler appears to perform type inference in a (fairly) strict top-to-bottom, left-to-right fashion. This means you must do things like put all definitions before th

Answer 1

The short answer is that F# is based on the tradition of SML and OCaml, whereas Haskell comes from a slightly different world of Miranda, Gofer, and the like. The differences in historical tradition are subtle, but pervasive. This distinction is paralleled in other modern languages too, such as the ML-like Coq which has the same ordering restrictions vs the Haskell-like Agda which doesn't.

This difference is related to lazy vs strict evaluation. The Haskell side of the universe believes in laziness, and once you already believe in laziness the idea of adding laziness to things like type inference is a no-brainer. Whereas in the ML side of the universe whenever laziness or mutual recursion is necessary it must be explicitly noted by the use of keywords like with, and, rec, etc. I prefer the Haskell approach because it results in less boilerplate code, but there are a lot of folks who think it's better to make these things explicit.