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Steele and Sussman
30
The Art of the Interpreter
(DEFINE (DRIVER-LOOP-1 ENV FORM)
(COND ((ATOM FORM)
(DRIVER-LOOP ENV (PRINT (EVAL FORM ENV))))
((EQ (CAR FORM) 'DEFINE)
(DRIVER-LOOP (LIST (CONS (CONS (CAADR FORM) (CAAR ENV))
(CONS (LIST '&LABELED
(CDADR FORM)
(CADDR FORM))
(CDAR ENV))))
(PRINT (CAADR FORM))))
(T (DRIVER-LOOP ENV (PRINT (EVAL FORM ENV))))))
(DEFINE (LOOKUP1 NAME VARS VALS ENV)
(COND ((NULL VARS)
(LOOKUP NAME (CDR ENV)))
((EQ NAME (CAR VARS))
(COND ((ATOM (CAR VALS)) VALS)
((EQ (CAAR VALS) '&LABELED)
(LIST '&PROCEDURE (CADAR VALS) (CADDAR VALS) ENV))
(T VALS)))
(T (LOOKUP1 NAME (CDR VARS) (CDR VALS) ENV))))
For DRIVER-LOOP see Figure 1.
For LOOKUP see Figure 3.
For EVAL see Figure 7.
Figure 10
An Alternative Solution for Local Lexical Scoping and Dynamic Top-Level References
(Modified Top-Level Driver Loop and Environment Lookup)
