[EMAIL PROTECTED] wrote:
I'm trying to understand first few pages of SICP where they explain
Scheme basics and had some newbie questions about evaluation....
** First of all, whenever you define a new function, the function's name and
function's code are stored in the "global environment". I thought
functional programming meant you weren't allowed to have any state. Yet,
modifying a "global environment" means changing state!?!?!?
Scheme is not a purely functional language so you can have mutable
state. Something like Haskell is purely functional and has no mutable
state. However, in functional programming you can often define a new
function and store it in the environment and then not be able to modify
it. Sort of like assign-once. I don't think scheme is this way but
Erlang is.
** Does the evaluation of functions return some mysterious type of object?
What the heck is going on? For example, look at evaluation of "+"...
As Brad said, + is a built in. It works like a function and could be
defined in terms of car's and cdr's but they have optimized it for speed.
** Also, what is the type of "define"? You cannot evaluate "define" so it
can't be a regular function.
It isn't. It is a syntactic keyword just like the error says. Scheme has
very few of these which is why it is so easy to learn the syntax of Scheme.
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