5.1.1.2.1 Examples of Setf Expansions

Examples of the contents of the constituents of setf expansions follow.

For a variable x:

()              ;list of temporary variables  
()              ;list of value forms          
(g0001)         ;list of store variables      
(setq x g0001)  ;storing form                 
x               ;accessing form               

Figure 5-3. Sample Setf Expansion of a Variable

For (car exp):

(g0002)                             ;list of temporary variables  
(exp)                               ;list of value forms          
(g0003)                             ;list of store variables      
(progn (rplaca g0002 g0003) g0003)  ;storing form                 
(car g0002)                         ;accessing form               

Figure 5-4. Sample Setf Expansion of a CAR Form

For (subseq seq s e):

(g0004 g0005 g0006)         ;list of temporary variables  
(seq s e)                   ;list of value forms          
(g0007)                     ;list of store variables      
(progn (replace g0004 g0007 :start1 g0005 :end1 g0006) g0007)                              
                            ;storing form                 
(subseq g0004 g0005 g0006)  ; accessing form              

Figure 5-5. Sample Setf Expansion of a SUBSEQ Form

In some cases, if a subform of a place is itself a place, it is necessary to expand the subform in order to compute some of the values in the expansion of the outer place. For (ldb bs (car exp)):

(g0001 g0002)            ;list of temporary variables  
(bs exp)                 ;list of value forms          
(g0003)                  ;list of store variables      
(progn (rplaca g0002 (dpb g0003 g0001 (car g0002))) g0003)                              
                         ;storing form                 
(ldb g0001 (car g0002))  ; accessing form              

Figure 5-6. Sample Setf Expansion of a LDB Form

• SETF-METHOD-VS-SETF-METHOD:RENAME-OLD-TERMS