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#lang eopl
; Ben Burwell
; Dr. Kussmaul
; CSI-310 :: Programming Languages
; Homework 6: Eta Conversion
;; ========== PROCEDURE ==========
;; NAME: eta-conv
;; DESC: takes a lambda expression and returns
;; its eta conversion. If the expression
;; does not have an eta-conversion, it
;; returns the expression itself.
(define eta-conv
(lambda (lst)
(if ;; check that the parameter is a list of length 3
(and
(list? lst)
(equal? (length lst) 3)
)
(if ;; it is a list with the correct length, check
;; that it has an eta-conversion
(and
(equal? (car lst) 'lambda)
(list? (cadr lst))
(equal? (length (cadr lst)) 1)
(list? (caddr lst))
(equal? (length (caddr lst)) 2)
(equal? (caadr lst) (cadr (caddr lst)))
)
;; it does, so return the conversion
(car (caddr lst))
;; it doesn't, so return the expression
lst)
;; not a parseable expression, return it
lst)))
;; ========== TEST CODE ==========
;; should return a:
(eta-conv '(lambda (x) (a x)))
;; should return (lambda (x) (x a))
(eta-conv '(lambda (x) (x a)))
;; should return ()
(eta-conv '())
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