From 2d5a2c3812e9eb7e07fa8ffaaba757eedaabdb02 Mon Sep 17 00:00:00 2001
From: Ben Burwell <bburwell1@gmail.com>
Date: Wed, 24 Apr 2013 16:59:38 -0400
Subject: Initial attempt

Still needs to handle expressions with multiple factors/terms; e.g.
1+2+3 or 2*3*4. Handles 1+2, 2*4, 1+2*3, etc.
---
 HW05b.scm | 96 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 HW05b.scm

diff --git a/HW05b.scm b/HW05b.scm
new file mode 100644
index 0000000..906ec38
--- /dev/null
+++ b/HW05b.scm
@@ -0,0 +1,96 @@
+#lang eopl
+
+(define scanner-spec
+  '(
+    (whitespace (whitespace) skip)
+    (number (digit (arbno digit)) make-number)
+    (operator ((or "+" "-" "*" "/" "(" ")")) make-symbol)))
+
+(define grammar
+  '(
+    (expression (term (arbno add-op term)) arith-expr)
+    (term (factor (arbno mult-op factor)) arith-factor)
+    (factor (number) number-factor)
+    (factor ("(" expression ")") expr-factor)
+    (add-op ("+") plus-op)
+    (add-op ("-") minus-op)
+    (mult-op ("*") times-op)
+    (mult-op ("/") divide-op)
+    ))
+
+(sllgen:make-define-datatypes scanner-spec grammar)
+(define dump-datatypes
+  (lambda ()
+    (sllgen:list-define-datatypes scanner-spec grammar)))
+
+
+(define execute-expression
+  (lambda (expr)
+    (cases expression expr
+      (arith-expr (term ops terms) (expr-helper term ops terms))
+      )))
+
+(define expr-helper
+  (lambda (term ops terms)
+    (if (null? ops)
+        (eval-term term)
+        (if (equal? (length ops) 1)
+            (eval-add-op (car ops) term (car terms))
+            
+            'a
+            
+            ))))
+
+(define eval-add-op
+  (lambda (op term1 term2)
+    (cases add-op op
+      (plus-op () (+ (eval-term term1) (eval-term term2)))
+      (minus-op () (- (eval-term term1) (eval-term term2)))
+      )))
+
+(define eval-term
+  (lambda (term1)
+    (cases term term1
+      (arith-factor (factor ops factors) (term-helper factor ops factors))
+      )))
+
+(define term-helper
+  (lambda (factor ops factors)
+    (if (null? ops)
+        (eval-factor factor)
+        (if (equal? (length ops) 1)
+            (eval-mult-op (car ops) factor (car factors))
+            
+            'b
+            
+            ))))
+
+(define eval-mult-op
+  (lambda (op fac1 fac2)
+    (cases mult-op op
+      (times-op () (* (eval-factor fac1) (eval-factor fac2)))
+      (divide-op () (/ (eval-factor fac1) (eval-factor fac2)))
+      )))
+
+(define eval-factor
+  (lambda (fac)
+    (cases factor fac
+      (number-factor (num) num)
+      (expr-factor (expr) (execute-expression expr))
+      )))
+  
+
+(define scan
+  (sllgen:make-string-scanner scanner-spec grammar))
+(define scan&parse
+  (sllgen:make-string-parser scanner-spec grammar))
+(define read-dump
+  (sllgen:make-rep-loop "> " (lambda (tree) tree) (sllgen:make-stream-parser scanner-spec grammar)))
+
+(define scan&parse&eval
+  (lambda (s) (execute-expression (scan&parse s))))
+
+(define read-eval-print
+  (sllgen:make-rep-loop "> " execute-expression (sllgen:make-stream-parser scanner-spec grammar)))
+
+(define spe scan&parse&eval)
\ No newline at end of file
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