On Thu, 15 Mar 2007, Robby Findler wrote:
This is not obvious to me. Doesn't simple substitution have the danger of
leading to exponential explosion in size due to unnecessary copying of the
argument throughout the body? I would think that this would happen for
many
common programs, making them harder to follow.
Substitution is a very simple way to think of function application,
going back to some of our earliest exposure to mathematics in school
(at least in this country).
I don't dispute that, but this is not how the text describes function
application.
While being pedagogical is not a bad secondary goal, a formal semantics must be
correct first. I would like to be able to reason about the space behaviour of
a program using the formal semantics. Direct substitution can change a
program's space behaviour from polynomial to exponential.
Given this, as far a space behaviour is concerned, the current semantics is
incorrect (compared with the body of the report).
Andre
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