lookahead

• here are the procedures that determine which branch of a rule to follow
• how far ahead does each rule look?
• (define (end?)
  
  (null? input))
  
  (define (assign?)
  (and (not (null? (cdr input)))
  (eq? (cadr input) ':=)))
  
  (define (compound?)
  (and (not (null? (cdr input)))
  (or (eq? (cadr input) '+)(eq? (cadr input) '*))))

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