From 5b05b64a2a658c0f7d4eb5b09fa342c7375a776e Mon Sep 17 00:00:00 2001
From: Ben Burwell <bburwell1@gmail.com>
Date: Thu, 11 Apr 2013 00:03:50 -0400
Subject: Init

---
 HW05a.scm | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 HW05a.scm

(limited to 'HW05a.scm')

diff --git a/HW05a.scm b/HW05a.scm
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+#lang eopl
+
+;; HW05a - Environments
+;;   Part 1: Procedural Implementation
+;;
+;; CSI-310 Programming Languages
+;; Due: 2013-02-25
+;; Name: Ben Burwell
+
+;; empty environment
+(define empty-env
+  (lambda ()
+    (lambda (sym) (eopl:error 'apply-env "No binding for ~s" sym))))
+
+;; helpers
+(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)) ]
+      )))
+
+;; extend environment
+(define extend-env
+  (lambda (sym-val-lst env)
+    (lambda (sym)
+       (if (in-sym-list sym sym-val-lst)
+           (get-val sym sym-val-lst)
+           (apply-env env sym)))))
+
+;; apply environment
+(define apply-env
+  (lambda (env sym)
+    (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)
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