On 3/20/07, Dan Weston
Dan Weston wrote:
Douglas Philips wrote:
On 2007 Mar 20, at 3:30 PM, Dan Weston indited:
I looked up John Backus on wikipedia and followed a link to ALGOL: http://en.wikipedia.org/wiki/ALGOL_60 where the following "undesirable" property of call-by-name is mentioned.
"ALGOL 60 allowed for two evaluation strategies for parameter passing: the common call-by-value, and call-by-name. Call-by-name had certain limitations in contrast to call-by-reference, making it an undesirable feature in language design. For example, it is impossible in ALGOL 60 to develop a procedure that will swap the values of two parameters if the actual parameters that are passed in are an integer variable and an array that is indexed by that same integer variable. However, call-by-name is still beloved of ALGOL implementors for the interesting thunks that are used to implement it."
I suppose that call-by-name is still beloved of Haskell implementors as well?
Notice that the "problem" with call-by-name is when side-effects are involved. In a pure-functional-environment those "problems" don't arise...
--Doug
It was the phrase "making it an undesirable feature in language design" that jumped out at me. Here "language" is an implicitly universally quantified variable, and the phrase beta-reduces to "call-by-name is an undesirable feature in Haskell design".
Ah, but since everything on wikipedia is true yet the conclusion you reached by beta-reduction is false, I believe you have shown that beta-reduction is invalid. That's alright though, I never liked function application much anyway.