[REBOL] Binding a changed function within a context
From: gscottjones:mchsi at: 5-Oct-2002 7:27
Hi, List,
I am working on an enhanced version of a field widget. In order to get the
enhanced functionality, I need to modify a function within the context of
edit-text in REBOL. The code is too long for easy use on the list (in my
opinion), so I have created a very simple example that (hopefully) recreates
the problem in the "small."
Here is my hypothetical context. It contains a local variable and a
function that prints that variable.
my-context: context [
local-var: 5
my-func: does [
print local-var
]
]
where then executing:
my-context/my-func ;yields 5
Now, let us say that I wish to dynamically change the function in this
object to the following:
my-func: does [
print ["new print" local-var]
]
where my-func will be bound into the context of my-context.
For your ease in running the code samples, I have included the original
context object with each example. In my non-hypothetical case, the shortest
code method would be to change the code in place like:
;### Method 1
;original
my-context: context [
local-var: 5
my-func: does [
print local-var
]
]
;make change
insert remove remove pick pick pick my-context 2 3 2 [print ["new print"
local-var]]
This makes my-context "look" correct (meaning that the data representation
of the code is correct when viewed with probe), but the inner function is
not bound into the context:
my-context/my-func ;expectedly yields an error
For completeness (to be sure that I understood the precept behind bind), I
also directly reassigned the function:
;### Method 2
;original
my-context: context [
local-var: 5
my-func: does [
print local-var
]
]
;make change
my-context/my-func: does [
print ["new print" local-var]
]
and again confirmed that an error occurs with my-context/my-func, because it
has not been bound into the context.
In the past, my tried and true way to make it work has been to "re-make" the
object with the new function:
;### Method 3
;original
my-context: context [
local-var: 5
my-func: does [
print local-var
]
]
;make change
my-context: make my-context [
my-func: does [
print ["new print" local-var]
]
]
which then works correctly when executing my-context/my-func (yields "new
print 5").
I understand the basic concepts behind scope and binding, and how these play
out in REBOL. It seems as though it should be easy enough to use bind, but
I can't figure out how to (successfully) do this when changing a function
within a context, at least with methods 1 and 2. Nothing wrong with method
3, but I would love to also be able to use method 1 or 2 with a
strategically and correctly placed bind statement. Any ideas?
--Scott Jones
