Hello, thanks a lot you got the point; I will never see that empty wasn't a function but just a constant name. Thanks also for the clear explanation.
Cheers Walter On Sat, 24 Sep 2011, [email protected] wrote:
Hello, Your problem here is that when you created your module stack, you wrote let empty = { c=[]} ;; which creates a global variable. Writing let s = empty creates a new stack by copying the value empty, therefore putting a type constraint, that s and empty must have the same type. In order to do what you want, you need to reevaluate the expression { c=[]} every time you create a new stack, and not just copy its result. This is achieved by using a function instead of a global variable: let empty () = { c=[]} an create a new stack with let s = empty () Hope it is not too confusing Cheers -Pierre Selon Walter Cazzola <[email protected]>:Hi all, thanks a lot for your help in this travel through OCaML but I have still a question. I have tried to write a polymorphic stack code attached but I don't understand its behavior: # open Stack;; # let s = empty;; val s : '_a Stack.stack = {c = []} # push s 7;; - : unit = () # push s 25;; - : unit = () # let s1 = empty;; val s1 : int Stack.stack = {c = [25; 7]} # push s1 "Hello";; Error: This expression has type string but an expression was expected of type int Apparently seems that I can have only a variable of type stack and any other call to its constructor links the new variable to the old one. This means that once I have put an int inside I can't have a second stack for characters or what else? This behavior is completely unexpected and I can't explain it. I'm sure I'm doing something wrong but I can't say what it is. Do you have any idea about? TIA Walter -- -- Caml-list mailing list. Subscription management and archives: https://sympa-roc.inria.fr/wws/info/caml-list Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
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