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
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