Init

3 files changed, 123 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))))
\ No newline at end of file
diff --git a/hw06/hw06_combinators.scm b/hw06/hw06_combinators.scm
new file mode 100644
index 0000000..0c3fdaf
--- /dev/null
+++ b/hw06/hw06_combinators.scm
@@ -0,0 +1,21 @@
+#lang eopl
+
+; Ben Burwell
+; Dr. Kussmaul
+; CSI-310 Programming Languages
+; HW06 :: Combinators
+
+; A. evaluate boolean logic expression
+(or F (and T (not F)))
+(or F (and T T))
+(or F T)
+T
+
+; B. compute 2+1 using Church numerals
+(increment 2)
+
+((λ (n) (λ (f) (λ (x) (f ((n                         f) x))))) (λ (f) (λ (x) (f (f x)))))
+(        λ (f) (λ (x) (f (((λ (f) (λ (x) (f (f x)))) f) x))))
+(        λ (f) (λ (x) (f (        (λ (x) (f (f x)))     x))))
+(        λ (f) (λ (x) (f                 (f (f x)))))
+(λ (f) (λ (x) (f (f (f x)))))
\ No newline at end of file
diff --git a/hw06/hw06_eta.scm b/hw06/hw06_eta.scm
new file mode 100644
index 0000000..991ee65
--- /dev/null
+++ b/hw06/hw06_eta.scm
@@ -0,0 +1,50 @@
+#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 '())