Add basic repl session management

src/ludus/repl.clj

@@ -4,7 +4,10 @@
     [ludus.parser :as parser]
     [ludus.interpreter :as interpreter]
     [ludus.prelude :as prelude]
-    [ludus.show :as show]))
+    [ludus.show :as show]
+    [ludus.data :as data]))
+
+(declare repl-prelude new-session)
 
 (def sessions (atom {}))
 
@@ -12,31 +15,71 @@
 
 (def prompt "=> ")
 
+(def base-ctx (merge prelude/prelude 
+	{::repl true "foo" :bar
+	 "repl"
+	 {
+	::data/struct true
+	::data/type ::data/ns
+	::data/name "repl"
+
+	:flush
+	{:name "flush"
+	 ::data/type ::data/clj
+	 :body (fn [] 
+	 	(let [session @current-session]
+	 		(swap! session #(assoc % :ctx (volatile! base-ctx)))
+	 		:ok))}
+
+    :new
+    {:name "new"
+	 ::data/type ::data/clj
+	 :body (fn [name]
+	 	(let [session (new-session name)]
+	 		(reset! current-session session)
+	 		:ok))}
+
+	:swap
+	{:name "swap"
+	::data/type ::data/clj
+	:body (fn [name]
+		(if-let [session (get @sessions name)]
+			(do
+				(reset! current-session session)
+				:ok)
+			(do
+				(println "No session named" name)
+				:error)))}
+	}}))
+
 (defn- new-session [name] 
   (let [session (atom {
                        :name name 
-                       :ctx (volatile! (merge prelude/prelude {::repl true})) 
+                       :ctx (volatile! base-ctx) 
                        :history []})]
     (swap! sessions #(assoc % name session))
     session))
 
-(defn repl-loop [session-atom]
-  (let [session @session-atom]
+(defn repl-loop []
+  (let [session-atom @current-session
+  	session @session-atom
+  	orig-ctx (:ctx session)]
     (print (str (:name session) prompt))
     (flush)
     (let [input (read-line)
           parsed (-> input (scanner/scan) (parser/parse))
           {result :result ctx :ctx} (interpreter/interpret-repl parsed (:ctx session))]
       (if (= result ::interpreter/error)
-        (repl-loop session-atom)
+        (repl-loop)
         (do
           (println (show/show result))
-          (swap! session-atom #(assoc % :ctx ctx))
-          (repl-loop session-atom))))))
+          (when (not (= @ctx @orig-ctx))
+          	(swap! session-atom #(assoc % :ctx ctx)))
+          (repl-loop))))))
 
 (defn launch []
   (println "Welcome to Ludus (v. 0.1.0-alpha)")
   (let [session (new-session "ludus")]
     (reset! current-session session)
-    (repl-loop session)))
+    (repl-loop)))