From: no.email@nospam.invalid   
      
   anton@mips.complang.tuwien.ac.at (Anton Ertl) writes:   
   > And if it's required to use every argument, then eager evaluation   
   > (call-by-value) is equivalent to Haskell's lazy evaluation.   
      
   "required to use every argument" and "strict evaluation" are sort of the   
   same thing.  The difference between strict and non-strict is what   
   happens if some of the args are not used, or only partially consumed.   
   With strict evaluation, passing 1/0 as an argument should raise an   
   error, and trying to create infinite list will run forever or exhaust   
   memory.  With non-strict, both of those are ok, and it's only an error   
   if you try to actually (e.g.) print the value.   
      
   CBN and lazy evaluation are two different strategies for implementing   
   non-strict evaluation.  If I'm using the jargon right, they have the   
   same denotational semantics, but different operational semantics.   
      
   > The way I have heard about Haskell programming up to now is that one   
   > tries to have a pure functional part, and then use monads at the   
   > fringes for things like I/O where pure functional code does not cut   
   > it.  I don't see this kind of separation in the Haskell code above.   
      
   I'll try to think of better explanation for this later, but basically   
   monads are just a notational trick, and I think that the Jensen's   
   example could have been done with the State monad instead of ST.  State   
   is purely functional and works by threading a value through a chain of   
   function evaluations.  ST (State Transformer) does sort of the same   
   thing as State, but it lets you use mutable memory cells, which can be   
   more efficient.   
      
   > I wonder if there is a more idiomatic way of writing this stuff in   
   > Haskell.   
      
   I don't see one offhand, except maybe with macros or some silly thing   
   like that.   
      
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