[Haskell-cafe] let and fixed point operator

[Albert Y. C. Lai]

Peter Hercek wrote:
> So the question is what am I missing? Any nice use cases where
>  fixed point search is so good that it is worth the trouble with
>  figuring out new and new variable names for essentially the same
>  stuff?

When I write functional code, I do find myself writing recursions much 
more often than writing imperative-wannabe assignments. I appreciate 
that Haskell's "let" defaults to recursion. I don't appreciate that 
OCaml makes a distinction between "let" and "letrec", since every time I 
change a non-recursive definition to a recursive one, I am prone to 
forget to change "let" to "letrec", IOW it is a hidden hazard to 
maintenance and evolution.

When I write imperative code in Haskell, the notation is so different 
from functional code that "let" doesn't even come into the equation.

When I write imperative code in imperative languages, my mental model 
treats "x:=x+1" as "x'=x+1 and y'=y and z'=z and ...", following several 
treatises on imperative semantics(*). Going back to functional 
programming, when I do write imperative-wannabe assignments, I totally 
like having names x, x', x'', etc., since they're in my head anyway.

Underlying all this is probably the soberness of recognizing that "=" is 
not ":=".


(*) Such as:

Eric C. R. Hehner, "A Practical Theory of Programming". First edition 
Springer 1993. Current edition at
http://www.cs.toronto.edu/~hehner/aPToP/

C. A. R. Hoare and He Jifeng, "Unifying Theories of Programming". 
Prentice Hall 1998.

The Z specification language.