+(define (ast-collect f x)
+ (define (inner y) (ast-collect f y))
+ (case (ast-type x)
+ ['let (append (f x)
+ (flat-map inner (let-bindings x))
+ (flat-map inner (let-body x)))]
+ ['app (append (f x)
+ (flat-map inner x))]
+ ['lambda (append (f x)
+ (inner (lambda-body x)))]
+ ['if (append (f x)
+ (flat-map inner (cdr x)))]
+ [else (f x)]))
+
+(define (ast-find p x)
+ (define (inner y) (ast-find p y))
+ (define (any p x) (fold-left
+ (lambda (acc y) (if acc #t (p y)))
+ #f
+ x))
+ (define (either . fs)
+ (if (null? fs) #f
+ (if (car fs) (car fs)
+ (apply either (cdr fs)))))
+
+ (case (ast-type x)
+ ['let (either (p x)
+ (any inner (let-bindings x))
+ (any inner (let-body x)))]
+ ['app (either (p x)
+ (any inner x))]
+ ['lambda (either (p x)
+ (inner (lambda-body x)))]
+ ['if (either (p x) (any inner (cdr x)))]
+ [else (p x)]))
+
+(define (let-bindings e)
+ (define (pattern-match x body)
+ (if (eqv? (ast-type x) 'var)
+ (cons x body)
+ (let* ([constructor (car x)]
+ [destructor (lambda (i) `(destruct ,i ,constructor))])
+ (flat-map (lambda (y i)
+ (pattern-match y (list (destructor i) body)))
+ (cdr x)
+ (range 0 (length (cdr x)))))))
+ (flat-map (lambda (x) (pattern-match (car x) (cdr x))) (cadr e)))