Paul Johnson wrote:
Andrew Coppin wrote:
PS. There is a technical distinction between the terms "lazy" and
"non-strict", and also the opposite terms "eger" and "strict". I
couldn't tell you what that is.
As I understand it, the distinction is between the mathematical term
"non-strict" and the implementation method of "lazy". "Non-strict"
means that "reduction" (the mathematical term for evaluation) proceeds
from the outside in, so if I have (a+(b*c)) then first you reduce the
"+", then you reduce the inner (b*c). Strict languages work the other
way around, starting with the innermost brackets and working outwards.
[...]
Almost right, but strict and non-strict aren't tied to an operational
semantics. In other words, you can talk about _|_ and strictness without
knowing how to evaluate your expressions at all. See also
http://en.wikibooks.org/wiki/Haskell/Denotational_semantics .
For more on the details of lazy evaluation (which actually does work
"outside in"), there's the incomplete
http://en.wikibooks.org/wiki/Haskell/Graph_reduction .
Of course, strict and eager as well as non-strict and lazy have pretty
much the same effect and can be used synonymously, but they're different
things nonetheless.
Regards,
apfelmus
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