Hello Simon, Wednesday, July 11, 2007, 11:38:31 AM, you wrote:
So Greg's idea (or at least my understanding thereof) is to write it like this:
do { f $(stuff1) $(stuff2) }
Simon, it is thing i dreamed for a years! Haskell has serious drawback for imperative programming compared to C - each action should be written as separate statement and this makes program too wordy - just try to rewrite something like x[i] += y[i]*z[i] in Haskell i need a way to perform actions and read data values inside calculations. there are two possible ways: * write pure expressions like we do in C and let's ghc guess yourself where evaluation should be added: x <- newIORef 1 y <- newIORef 1 z <- newIORef 1 f x (y*z) this means that any expression of type IORef a or IO a automatically translated into evaluation. the same should work for arrays, hashes and so on, so it probably should be a class. the problem, of course, is that IO/IORef/.. is a first class values so it's hard to distinguish where it should be evaluated and where used as is. another problem is its interaction with type inference - we may not know which concrete type this expression has * add an explicit operation which evaluates data, as you suggests. again, it should be a class which allows to add evaluation support for hashes/... actually, ML has something similar - it uses "." operation to evaluate variable values ============================================================================= and, while we on this topic, another problem for imperative programming style usability is control structures. how we can rewrite the following: delta=1000 while (delta>0.01) x = ... if (x<0) break delta = abs(n-x*x) ============================================================================= btw, proposal of "prefix expressions" also simplifies imperative programs a bit: now we should write something like this: when (a>0) $ do ..... while this proposal allows to omit "$" and make program look a bit more natural ============================================================================= one more complaint: the syntax for list $ \item -> do .... doesn't look too natural compared to other languages. it will be great to write it as for item in list do .... - of course, with 'for' still a plain function defined by user ============================================================================= may be, i should collect all these ideas on "imperative programming" page? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com