Assignment Question
Allright, I know this may be a stupid question, but it actually has a purpose,
cause this is really bugging me how the '$' operator messes up everything.
Why do I say that? Well, follow these examples
Example 1:
integer a
a = 1
>From reading this, we know that 'a' is declared as a variable, and that
variable is an integer. Plain and simple, right? Next step, we move to an
assignment operation, where we are assigning '1' to 'a'. Now, there's more
to it, then what I'm about to explain, but just hang in there, cause it'll
get more intresting here in a sec.
Internally, it's determined that we're assigning the value 1 to the variable
namespace of 'a'. Between the decloration of the variable namespace, the
assignment operator, and the actual value, there's a type-check done on '1'
to ensure that it'll fit in 'a', EG: we make sure that '1' is an integer,
and if it is, assign it to the variable, otherwise, we tell the user that
they are trying to put in the wrong type of data, into the variable. Now,
is this, or is this not correct?
We move on to Example 2:
integer a
a = 5 + 1
Now, this one is a bit more difficult, cause now, we're doing mathmatics in
the assignment statement. But, the thing is here, how does the interpreter
know that the value that 'a' should get, is '5 + 1', and not '6'? Well,
like before, this isn't exact, but first, the RHS get's evaluated, since it's
an expression, not a litteral. Meaning, that since it found the operator
'+', it now knows that '5' and '1' needs to be added together, before finally
assigning it to the variable namespace 'a'. Meaning now, that instead of
simply just assigning, we actually need to evaluate what the programmer means
when they do this.
Next Example:
function GetValue()
return 5
end function
integer a
a = GetValue()
Again, we have the basic decloration of the 'a' namespace as a variable, and
we have an assignment. But, we come back to the same problem, how do we know
that the user doesn't want to put 'GetValue()' into a? Cause the interpreter
knows, that it's earlier declared as a Function, and again, it catches the
fact, that it's a expression, that needs evaluated, before finally assigning
the data to a. If 'GetValue()' was a procedure, it would get evaluated, and
break out, cause no data is returned from 'GetValue()' as a procedure. And
again, the interpreter has to evaluate the final return value, to ensure that
the value can be put into the namespace, 'a', EG: it must be a integer.
Final Example:
function GetValue(integer b)
return b + 1
end function
integer a
a = GetValue(5)
This example, adds more complexity, but it remains the same, except for the
fact, now GetValue has a Private Member Space, in which 'b' is assigned to,
The interpreter knows, to assign 'b' the value of '5', cause of the order
of the arguments. Meaning basically, that 'integer b' and '(5)' becomes
'integer b b = 5' And the interpreter knows that it can't return the
litteral 'b + 1' from the call, cause it knows that 'b + 1' is an expression
which was evaluated first, before returning it to the caller, which in this
case is 'a = GetValue(5)'.
Throughout all of these examples, the interpreter didn't need to evaluate
'a' or 'b', cause it allready knew they was variable namespaces, and it knew
that they was an integer, only cause there was a need to assign data to it,
and when it came down to it, the RHS had to be evaluated first, before the
left hand side was.
So, Rob, you stated before, that it's not documented the exact behavior of
the interpreter, when you add something to a global sequence, from another
routine, we just experimented, and it worked that way. Well, it worked that
way, because it's an expression, and the interpreter knew that. It knew it
needed to evaluate the expression first, before Type Checking the data, and
finally assigning the data to the variable. The only difference now, is the
fact that instead of us pulling the rug out from under you, you've pulled
the rug out from under us. I guess my question is now, since this "feature"
was implemented, are we to expect that the way the rest of the assignments
are done, are going to change as well?
Mario Steele
P.S. Before anyone get's the wrong idea, I am not trying to beat down on
the interpreter, or the language construct, or Rob for that matter,
I am just pointing out a few things that are "Givens" in the Euphoria
Language, that don't need to be documented, cause they are the Basic
programming principals.
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