Matthew Brecknell wrote:
There is the question of whether it's preferable to use the "let" form or the "fix" form for embedding a recursive function in the middle of a do-block. I don't know if there's any consensus on this question, but it seems to me to be about whether one prefers to read a function top-down or bottom-up. I think I'm about 80/20 top-down/bottom-up. When I read a "let", I know (due to laziness) that it doesn't have any effect until the bindings are used, so I usually find myself scanning forward to find those uses. When I read "fix \f -> ...", I see exactly how the (anonymous) function is used, just before I get to its definition. So fix helps me to see things in a mostly top-down fashion.
If you're merely talking about top-down or bottom-up then there is also 'where' rather than 'let'. So the question becomes: 1. recursive definition first (let) 2. recursive definition last (where) 3. recursion inline (explicit use of fix) 1+2 have the virtue of separating the local recursive function from the 'main' function. On the other hand, 3 has the virtue of keeping them together :) Which you prefer is quite subjective, and context dependent. They potentially have slightly different scoping implications, too. A lot of discussion about haskell code revolves around whether or not a given construction is 'clear'; this has something to do with haskell's almost unparallelled ability to abstract, I suppose. Ultimately, something is clear once you are used to the abstraction, but obfuscated if you're not, so it becomes rather subjective. Jules