start work on interpreter

janet/interpreter.janet

@@ -0,0 +1,54 @@
+# A tree walk interpreter for ludus
+
+(var interpret nil)
+
+(defn- iff [ast ctx]
+  (def [condition then else] (ast :data))
+  (if (interpret condition ctx)
+    (interpret then ctx)
+    (interpret else ctx)))
+
+(defn- script [ast ctx]
+  (print "interpreting script")
+  (def lines (ast :data))
+  (var result nil)
+  (each line lines
+    (print "interpreting script line")
+    (set result (interpret line ctx)))
+  result)
+
+(defn- interpret* [ast ctx]
+  (print "interpreting ast node " (ast :type))
+  (case (ast :type)
+    :nil nil
+    :number (ast :data)
+    :bool (ast :data)
+    :string (ast :data)
+    :keyword (ast :data)
+    :if (iff ast ctx)
+    :script (script ast ctx)))
+
+(set interpret interpret*)
+
+# repl
+(try (os/cd "janet") ([_] nil))
+(import ./scanner :as s)
+(import ./parser :as p)
+(import ./validate :as v) 
+
+(var source nil)
+
+(defn run []
+  (def scanned (s/scan source))
+  (def parsed (p/parse scanned))
+  (def validated (v/valid parsed))
+  (pp parsed)
+  (interpret (parsed :ast) @{}))
+
+
+(do 
+(set source `
+if false then :bar else :baz
+`)
+(run)
+)