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Index
Setf Expansions Overview of Places and Generalized Reference Kinds of Places

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

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Overview of Places and Generalized Reference