Mailing List Archive: 49091 messages
  • Home
  • Script library
  • AltME Archive
  • Mailing list
  • Articles Index
  • Site search

[REBOL] Re: Binding

From: brett:codeconscious at: 20-Nov-2002 3:18

Hi Robert,
> Hi, ok I try again with the goal to finally understand this. Can't > believe it but even after years of Reboling it sometimes surprises me... > And I just read some of your words, etc. stuff from your Rebol page. But > it's really hard stuff...
I leave it to other to explain that code in more detail. I wanted to provide some different examples of words and their bindings just in case they help in understanding. I recommend pasting the script below into the console. Regards, Brett. ; The following four lines when executead establish the ; word "greeting" into four different contexts. greeting: {Hi!} australia: context [ greeting: {G'day!} greet: does [greeting] ] france: context [ greeting: {Salut!} greet: does [greeting] ] sweden: context [ greeting: {Hey!} greet: does [greeting] ] ; instances-of-greeting will contain four values ; of type word! all of which have the same name {greeting} ; but which differ in that each is bound to a different context. instances-of-greeting: reduce [ 'greeting in australia 'greeting in france 'greeting in sweden 'greeting ] ; Visually we might think it is the same word, but internally ; REBOL knows to keep them seperate. ?? instances-of-greeting reduce instances-of-greeting ; We can create an expression that will evaluate to a single value. expression: compose/deep [ rejoin [(instances-of-greeting)] ] ; Which can be evaluated like do expression ; But just because it looks like code doesn't mean we can't treat it ; as data. get expression/rejoin/1 get expression/rejoin/2 ; We can make a function from the expression by using the expression as ; the function body. f: does expression f ; Or demonstrate how the words in a function body are bound to the ; function arguments. g: func [ greeting ] expression g "Yo" ; Which is like using BIND on the expression itself - lets bind it to ; the swedish context. new-expression: bind/copy expression in sweden 'self do new-expression ; BIND changes the context of words in a block, so does FUNC to its ; body block. CONTEXT (make object!) also changes the context of ; words in a block it is given. ; In this next example, treat the script block as data like we did ; before. currency-name: "Dollar" script: [ euro-zone: context [ currency-name: "Euro" print-currency: does [print currency-name] ] ] get script/context/does/2 ; Now see the change after the script block is evaluated. do script get script/context/does/2 ; End of examples.