add basic evaluator, environment

1 files changed, 36 insertions, 0 deletions

diff --git a/prelude/primitives.scm b/prelude/primitives.scm
new file mode 100644
index 0000000..96dd1dd
--- /dev/null
+++ b/prelude/primitives.scm
@@ -0,0 +1,36 @@
+(define (true? expr) (eq? expr 'true))
+(define (false? expr) (eq? expr 'false))
+(define (bool? expr)
+  (or (true? expr)
+      (false? expr)))
+
+(define (and-special . items)
+  (if (null? items)
+      'false
+      (let ([first (car items)])
+        (cond
+          [(true? first) (apply and-special (cdr items))]
+          [(false? first) 'false]
+          [else (error "AND: unable to evaluate non-boolean form" first)]))))
+
+(define (or-special . items)
+  (if (null? items)
+      'false
+      (let ([first (car items)])
+        (cond
+          [(true? first) 'true]
+          [(false? first) (apply or-special (cdr items))]
+          [else (error "OR: unable to evaluate non-boolean form" first)]))))
+
+(define (not-fn x) (not (true? x)))
+
+(define primitives
+  `((+ . ,+)
+    (- . ,-)
+    (* . ,*)
+    (&& . ,and-special)
+    (|| . ,or-special)
+    (/= . ,not-fn)))
+
+(define (primitive-names) (map car primitives))
+(define (primitive-objs) (map cdr primitives))