Add basic lexenv support

src/lisp.c

@@ -57,7 +57,23 @@ void lisp_shutdown(void) {
     lisp_teardown_stack();
 }
 
-DEFUN(eval, "eval", (LispVal * form), "(form)", "") {
+static inline LispVal *lookup_variable(LispSymbol *name, LispVal *lexenv) {
+    LispVal *lexval = Fplist_get(lexenv, name, Qunbound);
+    if (lexval != Qunbound) {
+        return lexval;
+    }
+    if (name->value == Qunbound) {
+        // TODO better error
+        printf("Unbound symbol: ");
+        debug_print(stdout, name);
+        fputc('\n', stdout);
+        abort();
+    }
+    return name->value;
+}
+
+DEFUN(eval, "eval", (LispVal * form, LispVal *lexenv),
+      "(form &optional lexenv)", "") {
     if (!OBJECTP(form)) {
         // fixnum or float
         return form;
@@ -75,21 +91,12 @@ DEFUN(eval, "eval", (LispVal * form), "(form)", "") {
             out_data[i] = Qnil;
         }
         for (size_t i = 0; i < vec->length; ++i) {
-            out_data[i] = Feval(vec->data[i]);
+            out_data[i] = Feval(vec->data[i], lexenv);
         }
         return newvec;
     }
-    case TYPE_SYMBOL: {
-        // TODO local bindings
-        LispSymbol *sym = form;
-        if (sym->value == Qunbound) {
-            printf("Unbound symbol: ");
-            debug_print(stdout, form);
-            fputc('\n', stdout);
-            abort();
-        }
-        return sym->value;
-    }
+    case TYPE_SYMBOL:
+        return lookup_variable(form, lexenv);
     case TYPE_CONS: {
         return Ffuncall(XCAR(form), XCDR(form));
     }
@@ -131,7 +138,7 @@ void debug_print(FILE *file, LispVal *obj) {
     }
     case TYPE_CONS: {
         fputc('(', file);
-        FOREACH_TAIL(obj, tail) {
+        DOTAILS(tail, obj) {
             if (CONSP(tail)) {
                 debug_print(file, XCAR(tail));
                 if (!NILP(XCDR(tail))) {
@@ -162,6 +169,32 @@ void debug_print(FILE *file, LispVal *obj) {
     }
 }
 
+DEFSPECIAL(progn, "progn", (LispVal * forms), "(&rest forms)", "") {
+    LispVal *rval = Qnil;
+    DOLIST(form, forms) {
+        rval = Feval(form, TOP_LEXENV());
+    }
+    return rval;
+}
+
+DEFSPECIAL(let, "let", (LispVal * bindings, LispVal *body),
+           "(bindings &rest body)", "") {
+    CHECK_LISTP(bindings);
+    copy_parent_lexenv();
+    DOLIST(binding, bindings) {
+        if (SYMBOLP(binding)) {
+            new_lexical_variable(binding, Qnil);
+        } else if (CONSP(binding) && list_length_eq(binding, 2)) {
+            new_lexical_variable(FIRST(binding),
+                                 Feval(SECOND(binding), TOP_LEXENV()));
+        } else {
+            // TODO better error
+            abort();
+        }
+    }
+    return Fprogn(body);
+}
+
 void debug_obj_info(FILE *file, LispVal *obj) {
     fprintf(file, "%s -> ", LISP_TYPE_NAMES[TYPE_OF(obj)]);
     debug_print(file, obj);