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Diffstat (limited to 'hw06/hw06_alpha.scm')
| -rw-r--r-- | hw06/hw06_alpha.scm | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/hw06/hw06_alpha.scm b/hw06/hw06_alpha.scm new file mode 100644 index 0000000..1a6cb1b --- /dev/null +++ b/hw06/hw06_alpha.scm @@ -0,0 +1,52 @@ +#lang eopl + +; Ben Burwell +; Dr. Kussmaul +; CSI-310 :: Programming Languages +; Homework 6: Alpha conversions + +;; ========== PROCEDURE ========== +;; NAME: alpha-conv +;; DESC: returns the alpha conversion of an expression if +;; it exists. If there is no alpha conversion, the +;; expression itself is returned. +(define alpha-conv + (lambda (from to exp) + (if + (list? exp) + (if + (equal? (length exp) 3) + (if + (and + (equal? (car exp) 'lambda) + (list? (cadr exp)) + (equal? (length (cadr exp)) 1) + (list? (caddr exp)) + ) + (list 'lambda (list to) (list-repl from to (caddr exp))) + exp) + exp) + exp))) + +;; ========== PROCEDURE ========== +;; NAME: list-repl +;; DESC: a helper function for the alpha conversion +;; replaces all occurrences of from with to in +;; exp unless there is a nested lambda function, +;; in which case it remains intact. +(define list-repl + (lambda (from to exp) + (cond + [ (equal? (length exp) 0) '() ] + [ (equal? (car exp) from) (cons to (list-repl from to (cdr exp))) ] + [ (and (list? (car exp)) (equal? (caar exp) 'lambda)) (cons (car exp) (list-repl from to (cdr exp))) ] + [ (list? (car exp)) (cons (list-repl from to (car exp)) (list-repl from to (cdr exp))) ] + [ else (cons (car exp) (list-repl from to (cdr exp))) ] + ))) + +;; ========== TEST CODE ========== +(alpha-conv 'x 'y '(x z)) +(alpha-conv 'x 'y '((lambda ( x ) (+ x 5)) 2)) +(alpha-conv 'x 'y '(lambda ( x ) (x z x))) +(alpha-conv 'x 'y '(lambda ( y ) (y z y))) +(alpha-conv 'x 'y '(lambda ( x ) (+ x ((lambda (x) (* 2 x)) 7))))
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