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+#lang eopl
+
+;; HW05a - Environments
+;;   Part 3: Rib-Cage Implementation
+;;
+;; CSI-310 Programming Languages
+;; Due: 2013-02-25
+;; Name: Ben Burwell
+
+;; empty environment
+(define empty-env
+  (lambda () '(())
+    ))
+
+;; extend environment
+(define extend-env
+  (lambda (sym-val-lst env)
+    (cons sym-val-lst env)))
+
+;; helper
+(define in-sym-list?
+  (lambda (item lst)
+    (cond
+      [ (equal? (length lst) 0) #f ]
+      [ (equal? (caar lst) item) #t ]
+      [ else (in-sym-list? item (cdr lst)) ]
+      )))
+
+(define get-val
+  (lambda (sym lst)
+    (cond
+      [ (equal? (length lst) 0) 'err ]
+      [ (equal? (caar lst) sym) (cadar lst) ]
+      [ else (get-val sym (cdr lst)) ]
+      )))
+
+;; apply environment
+(define apply-env
+  (lambda (env sym)
+    (cond
+      [ (in-sym-list? sym (car env)) (get-val sym (car env)) ]
+      [ (equal? (length (car env)) 0) (eopl:error "No binding for" sym) ]
+      [ else (apply-env (cdr env) sym) ]
+      )))
+
+
+;; tests
+(apply-env (extend-env '((a 5) (b 9)) (extend-env '((a 1) (b 2) (c 3)) (empty-env))) 'a)
+(apply-env (extend-env '((a 5) (b 9)) (extend-env '((a 1) (b 2) (c 3)) (empty-env))) 'b)
+(apply-env (extend-env '((a 5) (b 9)) (extend-env '((a 1) (b 2) (c 3)) (empty-env))) 'c)
+\ No newline at end of file