Deferred Words

Often, you know how to use a word X within word Y, but want to defer defining X for later or maybe want to use a variety of versions of X such as X1, X2.

  • The best way to do this is passing the XT into the word using the stack (i.e. function binding).
  • The alternative is to define a global word which has no real code body, then bind that name to an XT at runtime.

    • To create the "blank" word, we use 
    DEFER
    . For example, to create a blank word 
    XX
    , we do the following:
	
    	defer xx
	
    
	
	
    You can use the word 
    XX
     anywhere subsequently. To put in some functionality, use 
    AS
    . The behaviour can also be changed subsequently at any time using 
    AS
    .
	
    	
	: x2 "pug!" . ;
	
	' x2 as xx
	
	xx
	pug! ok	
	
    	

	
	
    Quiz
    
	
    Question 1
    
	
    Before putting in some functionality into 
    XX
    . What does 
    DEFER XX
     do? Check your answer using 
    SEE
    .
    
	
	
	

    
	

	
    Question 2
    
	
    What happens if we run 
    XX
     before it is given any functionality?
    
	
	
	

    
	
	
	
    Question 3
    
	
    	
	: compose ( xt xt -- xt ) 
	     { f g } [: f execute g execute ;] ;
	
     		
	
    Rewrite 
    COMPOSE
     without using local variables or local functions. Use 
    DEFER
     instead.
    
	
	
	

    
	
 
    Next: Recursive Sequences