[REBOL] Re: Binding a changed function within a context
From: brett:codeconscious at: 6-Oct-2002 15:24
For amusement, below are some examples of words bound to different contexts.
Just move throught the code by copying from the email and pasting bits of it
at a time into the console.
Regards,
Brett.
;
; Amusement 1
;
; BIND matches up words it can find in the target context.
ctx-1: context [country: "Australia"]
ctx-2: context [city: "Sydney"]
ctx-3: context [name: "Brett"]
expression: [join name [{ lives in } city {, } country]]
repeat ctx reduce [ctx-1 ctx-2 ctx-3] [bind expression in ctx 'self]
print expression
;
; Functions create a new context binding the words of their body block
; to their arguments:
my-func: func [name] expression
my-func "My wife"
;
; Amusement 2
;
; This first bit is straight forward - what appears to be
; nesting of contexts. As others have pointed out (probably
; more clearly than me) this is an effective or apparent
; nesting.
ctx-1: context [
word-a: #1a
word-b: #1b
word-c: #1c
ctx-2: context [
word-a: #2a
word-b: #2b
ctx-3: context [
word-a: #3a
set 'print-it does [
print ["First function" word-a word-b word-c]
]
]
]
]
print-it
;
; We can simulate the apparent scoping of CONTEXT with
; script that is obviously not nested...
;
ctx-1: context [word-a: #1a word-b: #1b word-c: #1c]
ctx-2: context [word-a: #2a word-b: #2b]
ctx-3: context [word-a: #3a]
contexts: reduce [ctx-1 ctx-2 ctx-3]
expression: [print ["Expression" word-a word-b word-c]]
repeat ctx contexts [bind expression in ctx 'self]
do expression
;
; Or indeed reverse it, or perhaps do other odd
; bindings.
;
reverse contexts
repeat ctx contexts [bind expression in ctx 'self]
do expression
;
; Amusement 3
;
; REBOL represents words to you using
; their names but does not have a visual representation for
; the context of those words.
; When you print the mold of the expression of this example
; you cannot see the difference between the two words that
; have the same name 'sample-word.
; Philosophical point:
; It is easy to fall into the trap of mistaking the name
; of a thing for the thing itself. As always with REBOL,
; the items you see in the console or in a file are not
; the things themselves but representations of the things.
ctx-1: context [sample-word: "Context1"]
ctx-2: context [sample-word: "Context2"]
expression: [{A word: }]
append expression in ctx-1 'sample-word
append expression [{^/A different word with the same name: }]
append expression in ctx-2 'sample-word
print expression
; This last example was admittedly contrived, and you
; wouldn't expect to see it used much. But I think
; it has value in showing a different way to look at
; REBOL words.
