Add readFromEnvironment() for reading without cloning.

Define the REPL prompt in the environment.

src/env.c

@@ -23,6 +23,11 @@ void setGlobal(struct Environment* env)
 struct Dictionary dictionary;
 
 Object fetchFromEnvironment(const char* name, struct Environment* env)
+{
+    return cloneObject(readFromEnvironment(name, env));
+}
+
+Object readFromEnvironment(const char* name, struct Environment* env)
 {
     if (!env) {
         return errorObject(NULL_ENV);
@@ -30,7 +35,7 @@ Object fetchFromEnvironment(const char* name, struct Environment* env)
 
     if (env->capacity == 0) {
         if (env->outer) {
-            return fetchFromEnvironment(name, env->outer);
+            return readFromEnvironment(name, env->outer);
         } else {
             return errorObject(EMPTY_ENV);
         }
@@ -43,13 +48,13 @@ Object fetchFromEnvironment(const char* name, struct Environment* env)
 
         printd("Try %d (%s)\n", i, env->strings[i]);
         if (strcmp(name, env->strings[i]) == 0) { printd("Returning!\n");
-            return cloneObject(env->objects[i]);
+            return env->objects[i];
         }
     }
 
     printd("Trying outer %p\n", env->outer);
     if (env->outer) {
-        return fetchFromEnvironment(name, env->outer);
+        return readFromEnvironment(name, env->outer);
     }
 
     return errorWithContext(DID_NOT_FIND_SYMBOL, name);

src/env.h

@@ -23,6 +23,9 @@ struct Environment* global();
 
 void setGlobal(struct Environment* env);
 
+/// Does NOT clone
+Object readFromEnvironment(const char* name, struct Environment* env);
+
 Object fetchFromEnvironment(const char* name, struct Environment* env);
 
 struct Environment envForLambda(const Object* params, const Object* arg_forms, int paramCount,

src/pebblisp.c

@@ -600,12 +600,15 @@ void repl(struct Environment* env)
 {
     char* buf;
     using_history();
-    while ((buf = readline("pebblisp::> ")) != NULL) {
+    parseEval("(def prompt \"pebblisp::> \")", env);
+    while ((buf = readline(readFromEnvironment("prompt", env).string)) != NULL) {
         if (strcmp("q", buf) == 0) {
             free(buf);
             break;
         }
-        add_history(buf);
+        if (buf[0] != '\0') {
+            add_history(buf);
+        }
         if (buf[0] == '?' && (buf[1] == ' ' || buf[1] == '\0')) {
             char* oldBuf = buf;
             buf = malloc(sizeof(char) * strlen(buf + 3));