add basic evaluator, environment

2 files changed, 33 insertions, 0 deletions

diff --git a/util/alist.scm b/util/alist.scm
new file mode 100644
index 0000000..4e19440
--- /dev/null
+++ b/util/alist.scm
@@ -0,0 +1,12 @@
+(define (is-elem-assoc-list key assoc-list)
+  (cond
+    [(null? assoc-list) #f]
+    [(eq? key (caar assoc-list)) #t]
+    [else (lookup-assoc-list key (cdr assoc-list))]))
+
+(define (lookup-assoc-list key assoc-list)
+  (cond
+    [(null? assoc-list) #f]
+    [(eq? key (caar assoc-list)) (cdar assoc-list)]
+    [else (lookup-assoc-list key (cdr assoc-list))]))
+
diff --git a/util/table.scm b/util/table.scm
new file mode 100644
index 0000000..7cc68e8
--- /dev/null
+++ b/util/table.scm
@@ -0,0 +1,21 @@
+(define (make-table)
+  (list '*table*))
+
+(define (key-assoc key records)
+  (cond
+    [(null? records) #f]
+    [(equal? key (caar records)) (car records)]
+    [else (key-assoc key (cdr records))]))
+
+(define (lookup key table)
+  (let ([r (key-assoc key (cdr table))])
+    (if r
+        (cdr r)
+        #f)))
+
+(define (table-insert! key value table)
+  (let ([r (key-assoc key (cdr table))])
+    (if r
+        (set-cdr! r value)
+        (set-cdr! table (cons (cons key value)
+                              (cdr table))))))