altos: Add lambda support to lisp

Signed-off-by: Keith Packard <keithp@keithp.com>

14 files changed, 528 insertions, 165 deletions

diff --git a/src/lisp/Makefile b/src/lisp/Makefile
index 9e2fb58c..be19b432 100644
--- a/src/lisp/Makefile
+++ b/src/lisp/Makefile
@@ -17,7 +17,8 @@ SRCS=\
 	ao_lisp_prim.c \
 	ao_lisp_builtin.c \
 	ao_lisp_read.c \
-	ao_lisp_frame.c
+	ao_lisp_frame.c \
+	ao_lisp_error.c
 
 OBJS=$(SRCS:.c=.o)
 
diff --git a/src/lisp/ao_lisp.h b/src/lisp/ao_lisp.h
index 98e99acb..9a5cc63e 100644
--- a/src/lisp/ao_lisp.h
+++ b/src/lisp/ao_lisp.h
@@ -32,11 +32,22 @@
 extern uint8_t ao_lisp_const[AO_LISP_POOL_CONST];
 #define ao_lisp_pool ao_lisp_const
 #define AO_LISP_POOL AO_LISP_POOL_CONST
-#define _ao_lisp_atom_quote ao_lisp_atom_poly(ao_lisp_atom_intern("quote"))
-#define _ao_lisp_atom_set ao_lisp_atom_poly(ao_lisp_atom_intern("set"))
+
+#define _atom(n) ao_lisp_atom_poly(ao_lisp_atom_intern(n))
+
+#define _ao_lisp_atom_quote	_atom("quote")
+#define _ao_lisp_atom_set 	_atom("set")
+#define _ao_lisp_atom_setq 	_atom("setq")
+#define _ao_lisp_atom_t 	_atom("t")
+#define _ao_lisp_atom_car 	_atom("car")
+#define _ao_lisp_atom_cdr	_atom("cdr")
+#define _ao_lisp_atom_cons	_atom("cons")
+#define _ao_lisp_atom_cond	_atom("cond")
 #else
 #include "ao_lisp_const.h"
+#ifndef AO_LISP_POOL
 #define AO_LISP_POOL	1024
+#endif
 extern uint8_t		ao_lisp_pool[AO_LISP_POOL];
 #endif
 
@@ -68,6 +79,7 @@ extern uint16_t		ao_lisp_top;
 extern uint8_t		ao_lisp_exception;
 
 typedef uint16_t	ao_poly;
+typedef int16_t		ao_signed_poly;
 
 static inline int
 ao_lisp_is_const(ao_poly poly) {
@@ -157,6 +169,7 @@ enum ao_lisp_builtin_id {
 	builtin_quote,
 	builtin_set,
 	builtin_setq,
+	builtin_cond,
 	builtin_print,
 	builtin_plus,
 	builtin_minus,
@@ -222,13 +235,13 @@ ao_lisp_cons_poly(struct ao_lisp_cons *cons)
 static inline int
 ao_lisp_poly_int(ao_poly poly)
 {
-	return (int) poly >> AO_LISP_TYPE_SHIFT;
+	return (int) ((ao_signed_poly) poly >> AO_LISP_TYPE_SHIFT);
 }
 
 static inline ao_poly
 ao_lisp_int_poly(int i)
 {
-	return ((ao_poly) i << 2) + AO_LISP_INT;
+	return ((ao_poly) i << 2) | AO_LISP_INT;
 }
 
 static inline char *
@@ -326,8 +339,7 @@ extern const struct ao_lisp_type ao_lisp_atom_type;
 
 extern struct ao_lisp_atom *ao_lisp_atoms;
 
-void
-ao_lisp_atom_init(void);
+extern struct ao_lisp_frame *ao_lisp_frame_current;
 
 void
 ao_lisp_atom_print(ao_poly a);
@@ -359,12 +371,27 @@ ao_lisp_poly_move(ao_poly p);
 ao_poly
 ao_lisp_eval(ao_poly p);
 
+ao_poly
+ao_lisp_set_cond(struct ao_lisp_cons *cons);
+
 /* builtin */
 void
 ao_lisp_builtin_print(ao_poly b);
 
 extern const struct ao_lisp_type ao_lisp_builtin_type;
 
+/* Check argument count */
+ao_poly
+ao_lisp_check_argc(ao_poly name, struct ao_lisp_cons *cons, int min, int max);
+
+/* Check argument type */
+ao_poly
+ao_lisp_check_argt(ao_poly name, struct ao_lisp_cons *cons, int argc, int type, int nil_ok);
+
+/* Fetch an arg (nil if off the end) */
+ao_poly
+ao_lisp_arg(struct ao_lisp_cons *cons, int argc);
+
 /* read */
 ao_poly
 ao_lisp_read(void);
@@ -376,11 +403,8 @@ ao_lisp_read_eval_print(void);
 /* frame */
 extern const struct ao_lisp_type ao_lisp_frame_type;
 
-int
-ao_lisp_frame_set(struct ao_lisp_frame *frame, ao_poly atom, ao_poly val);
-
-ao_poly
-ao_lisp_frame_get(struct ao_lisp_frame *frame, ao_poly atom);
+ao_poly *
+ao_lisp_frame_ref(struct ao_lisp_frame *frame, ao_poly atom);
 
 struct ao_lisp_frame *
 ao_lisp_frame_new(int num, int readonly);
@@ -388,4 +412,9 @@ ao_lisp_frame_new(int num, int readonly);
 struct ao_lisp_frame *
 ao_lisp_frame_add(struct ao_lisp_frame *frame, ao_poly atom, ao_poly val);
 
+/* error */
+
+ao_poly
+ao_lisp_error(int error, char *format, ...);
+
 #endif /* _AO_LISP_H_ */
diff --git a/src/lisp/ao_lisp_atom.c b/src/lisp/ao_lisp_atom.c
index e5d28c3b..ea04741e 100644
--- a/src/lisp/ao_lisp_atom.c
+++ b/src/lisp/ao_lisp_atom.c
@@ -109,31 +109,65 @@ ao_lisp_atom_intern(char *name)
 	return atom;
 }
 
-static struct ao_lisp_frame	*globals;
+static struct ao_lisp_frame	*ao_lisp_frame_global;
+struct ao_lisp_frame		*ao_lisp_frame_current;
+
+static void
+ao_lisp_atom_init(void)
+{
+	if (!ao_lisp_frame_global) {
+		ao_lisp_frame_global = ao_lisp_frame_new(0, 0);
+		ao_lisp_root_add(&ao_lisp_frame_type, &ao_lisp_frame_global);
+		ao_lisp_root_add(&ao_lisp_frame_type, &ao_lisp_frame_current);
+	}
+}
+
+static ao_poly *
+ao_lisp_atom_ref(struct ao_lisp_frame *frame, ao_poly atom)
+{
+	ao_poly	*ref;
+	ao_lisp_atom_init();
+	while (frame) {
+		ref = ao_lisp_frame_ref(frame, atom);
+		if (ref)
+			return ref;
+		frame = ao_lisp_poly_frame(frame->next);
+	}
+	if (ao_lisp_frame_global) {
+		ref = ao_lisp_frame_ref(ao_lisp_frame_global, atom);
+		if (ref)
+			return ref;
+	}
+	return NULL;
+}
 
 ao_poly
 ao_lisp_atom_get(ao_poly atom)
 {
-	struct ao_lisp_frame	*frame = globals;
+	ao_poly *ref = ao_lisp_atom_ref(ao_lisp_frame_current, atom);
+
+	if (!ref && ao_lisp_frame_global)
+		ref = ao_lisp_frame_ref(ao_lisp_frame_global, atom);
 #ifdef ao_builtin_frame
-	if (!frame)
-		frame = ao_lisp_poly_frame(ao_builtin_frame);
+	if (!ref)
+		ref = ao_lisp_frame_ref(ao_lisp_poly_frame(ao_builtin_frame), atom);
 #endif
-	return ao_lisp_frame_get(frame, atom);
+	if (ref)
+		return *ref;
+	return AO_LISP_NIL;
 }
 
 ao_poly
 ao_lisp_atom_set(ao_poly atom, ao_poly val)
 {
-	if (!ao_lisp_frame_set(globals, atom, val)) {
-		globals = ao_lisp_frame_add(globals, atom, val);
-		if (!globals->next) {
-			ao_lisp_root_add(&ao_lisp_frame_type, &globals);
-#ifdef ao_builtin_frame
-			globals->next = ao_builtin_frame;
-#endif
-		}
-	}
+	ao_poly *ref = ao_lisp_atom_ref(ao_lisp_frame_current, atom);
+
+	if (!ref && ao_lisp_frame_global)
+		ref = ao_lisp_frame_ref(ao_lisp_frame_global, atom);
+	if (ref)
+		*ref = val;
+	else
+		ao_lisp_frame_global = ao_lisp_frame_add(ao_lisp_frame_global, atom, val);
 	return val;
 }
 
diff --git a/src/lisp/ao_lisp_builtin.c b/src/lisp/ao_lisp_builtin.c
index 8c481793..2976bc95 100644
--- a/src/lisp/ao_lisp_builtin.c
+++ b/src/lisp/ao_lisp_builtin.c
@@ -46,7 +46,8 @@ ao_lisp_builtin_print(ao_poly b)
 	printf("[builtin]");
 }
 
-static int check_argc(struct ao_lisp_cons *cons, int min, int max)
+ao_poly
+ao_lisp_check_argc(ao_poly name, struct ao_lisp_cons *cons, int min, int max)
 {
 	int	argc = 0;
 
@@ -54,28 +55,30 @@ static int check_argc(struct ao_lisp_cons *cons, int min, int max)
 		argc++;
 		cons = ao_lisp_poly_cons(cons->cdr);
 	}
-	if (argc < min || argc > max) {
-		ao_lisp_exception |= AO_LISP_INVALID;
-		return 0;
-	}
-	return 1;
+	if (argc < min || argc > max)
+		return ao_lisp_error(AO_LISP_INVALID, "%s: invalid arg count", ao_lisp_poly_atom(name)->name);
+	return _ao_lisp_atom_t;
 }
 
-static int check_argt(struct ao_lisp_cons *cons, int argc, int type, int nil_ok)
+ao_poly
+ao_lisp_arg(struct ao_lisp_cons *cons, int argc)
 {
-	ao_poly car;
-
-	/* find the desired arg */
-	while (argc--)
+	while (argc--) {
+		if (!cons)
+			return AO_LISP_NIL;
 		cons = ao_lisp_poly_cons(cons->cdr);
-	car = cons->car;
-	if ((!car && !nil_ok) ||
-	    ao_lisp_poly_type(car) != type)
-	{
-		ao_lisp_exception |= AO_LISP_INVALID;
-		return 0;
 	}
-	return 1;
+	return cons->car;
+}
+
+ao_poly
+ao_lisp_check_argt(ao_poly name, struct ao_lisp_cons *cons, int argc, int type, int nil_ok)
+{
+	ao_poly car = ao_lisp_arg(cons, argc);
+
+	if ((!car && !nil_ok) || ao_lisp_poly_type(car) != type)
+		return ao_lisp_error(AO_LISP_INVALID, "%s: invalid type for arg %d", ao_lisp_poly_atom(name)->name, argc);
+	return _ao_lisp_atom_t;
 }
 
 enum math_op { math_plus, math_minus, math_times, math_divide, math_mod };
@@ -83,30 +86,20 @@ enum math_op { math_plus, math_minus, math_times, math_divide, math_mod };
 ao_poly
 ao_lisp_car(struct ao_lisp_cons *cons)
 {
-	if (!check_argc(cons, 1, 1))
+	if (!ao_lisp_check_argc(_ao_lisp_atom_car, cons, 1, 1))
 		return AO_LISP_NIL;
-	if (!check_argt(cons, 0, AO_LISP_CONS, 0)) {
-		ao_lisp_exception |= AO_LISP_INVALID;
+	if (!ao_lisp_check_argt(_ao_lisp_atom_car, cons, 0, AO_LISP_CONS, 0))
 		return AO_LISP_NIL;
-	}
 	return ao_lisp_poly_cons(cons->car)->car;
 }
 
 ao_poly
 ao_lisp_cdr(struct ao_lisp_cons *cons)
 {
-	if (!cons) {
-		ao_lisp_exception |= AO_LISP_INVALID;
+	if (!ao_lisp_check_argc(_ao_lisp_atom_cdr, cons, 1, 1))
 		return AO_LISP_NIL;
-	}
-	if (!cons->car) {
-		ao_lisp_exception |= AO_LISP_INVALID;
-		return AO_LISP_NIL;
-	}
-	if (ao_lisp_poly_type(cons->car) != AO_LISP_CONS) {
-		ao_lisp_exception |= AO_LISP_INVALID;
+	if (!ao_lisp_check_argt(_ao_lisp_atom_cdr, cons, 0, AO_LISP_CONS, 0))
 		return AO_LISP_NIL;
-	}
 	return ao_lisp_poly_cons(cons->car)->cdr;
 }
 
@@ -114,50 +107,39 @@ ao_poly
 ao_lisp_cons(struct ao_lisp_cons *cons)
 {
 	ao_poly	car, cdr;
-	if (!cons) {
-		ao_lisp_exception |= AO_LISP_INVALID;
-		return AO_LISP_NIL;
-	}
-	car = cons->car;
-	cdr = cons->cdr;
-	if (!car || !cdr) {
-		ao_lisp_exception |= AO_LISP_INVALID;
+	if(!ao_lisp_check_argc(_ao_lisp_atom_cons, cons, 2, 2))
 		return AO_LISP_NIL;
-	}
-	cdr = ao_lisp_poly_cons(cdr)->car;
-	if (ao_lisp_poly_type(cdr) != AO_LISP_CONS) {
-		ao_lisp_exception |= AO_LISP_INVALID;
+	if (!ao_lisp_check_argt(_ao_lisp_atom_cons, cons, 1, AO_LISP_CONS, 1))
 		return AO_LISP_NIL;
-	}
+	car = ao_lisp_arg(cons, 0);
+	cdr = ao_lisp_arg(cons, 1);
 	return ao_lisp_cons_poly(ao_lisp_cons_cons(car, ao_lisp_poly_cons(cdr)));
 }
 
 ao_poly
 ao_lisp_quote(struct ao_lisp_cons *cons)
 {
-	if (!cons) {
-		ao_lisp_exception |= AO_LISP_INVALID;
+	if (!ao_lisp_check_argc(_ao_lisp_atom_quote, cons, 1, 1))
 		return AO_LISP_NIL;
-	}
-	return cons->car;
+	return ao_lisp_arg(cons, 0);
 }
 
 ao_poly
 ao_lisp_set(struct ao_lisp_cons *cons)
 {
-	if (!check_argc(cons, 2, 2))
+	if (!ao_lisp_check_argc(_ao_lisp_atom_set, cons, 2, 2))
 		return AO_LISP_NIL;
-	if (!check_argt(cons, 0, AO_LISP_ATOM, 0))
+	if (!ao_lisp_check_argt(_ao_lisp_atom_set, cons, 0, AO_LISP_ATOM, 0))
 		return AO_LISP_NIL;
 
-	return ao_lisp_atom_set(cons->car, ao_lisp_poly_cons(cons->cdr)->car);
+	return ao_lisp_atom_set(ao_lisp_arg(cons, 0), ao_lisp_poly_cons(ao_lisp_arg(cons, 1))->car);
 }
 
 ao_poly
 ao_lisp_setq(struct ao_lisp_cons *cons)
 {
 	struct ao_lisp_cons	*expand = 0;
-	if (!check_argc(cons, 2, 2))
+	if (!ao_lisp_check_argc(_ao_lisp_atom_setq, cons, 2, 2))
 		return AO_LISP_NIL;
 	expand = ao_lisp_cons_cons(_ao_lisp_atom_set,
 				   ao_lisp_cons_cons(ao_lisp_cons_poly(ao_lisp_cons_cons(_ao_lisp_atom_quote,
@@ -167,6 +149,22 @@ ao_lisp_setq(struct ao_lisp_cons *cons)
 }
 
 ao_poly
+ao_lisp_cond(struct ao_lisp_cons *cons)
+{
+	int			argc;
+	struct ao_lisp_cons	*arg;
+
+	argc = 0;
+	for (arg = cons, argc = 0; arg; arg = ao_lisp_poly_cons(arg->cdr), argc++) {
+		if (ao_lisp_poly_type(arg->car) != AO_LISP_CONS)
+			return ao_lisp_error(AO_LISP_INVALID, "%s: invalid type for arg %d",
+					     ao_lisp_poly_atom(_ao_lisp_atom_cond)->name, argc);
+	}
+	ao_lisp_set_cond(cons);
+	return AO_LISP_NIL;
+}
+
+ao_poly
 ao_lisp_print(struct ao_lisp_cons *cons)
 {
 	ao_poly	val = AO_LISP_NIL;
@@ -210,17 +208,13 @@ ao_lisp_math(struct ao_lisp_cons *cons, enum math_op op)
 				r *= c;
 				break;
 			case math_divide:
-				if (c == 0) {
-					ao_lisp_exception |= AO_LISP_DIVIDE_BY_ZERO;
-					return AO_LISP_NIL;
-				}
+				if (c == 0)
+					return ao_lisp_error(AO_LISP_DIVIDE_BY_ZERO, "divide by zero");
 				r /= c;
 				break;
 			case math_mod:
-				if (c == 0) {
-					ao_lisp_exception |= AO_LISP_DIVIDE_BY_ZERO;
-					return AO_LISP_NIL;
-				}
+				if (c == 0)
+					return ao_lisp_error(AO_LISP_DIVIDE_BY_ZERO, "mod by zero");
 				r %= c;
 				break;
 			}
@@ -230,10 +224,8 @@ ao_lisp_math(struct ao_lisp_cons *cons, enum math_op op)
 		else if (rt == AO_LISP_STRING && ct == AO_LISP_STRING && op == math_plus)
 			ret = ao_lisp_string_poly(ao_lisp_string_cat(ao_lisp_poly_string(ret),
 								     ao_lisp_poly_string(car)));
-		else {
-			ao_lisp_exception |= AO_LISP_INVALID;
-			return AO_LISP_NIL;
-		}
+		else
+			return ao_lisp_error(AO_LISP_INVALID, "invalid args");
 	}
 	return ret;
 }
@@ -275,6 +267,7 @@ ao_lisp_func_t ao_lisp_builtins[] = {
 	[builtin_quote] = ao_lisp_quote,
 	[builtin_set] = ao_lisp_set,
 	[builtin_setq] = ao_lisp_setq,
+	[builtin_cond] = ao_lisp_cond,
 	[builtin_print] = ao_lisp_print,
 	[builtin_plus] = ao_lisp_plus,
 	[builtin_minus] = ao_lisp_minus,
diff --git a/src/lisp/ao_lisp_const.lisp b/src/lisp/ao_lisp_const.lisp
index aa356d45..5ee15899 100644
--- a/src/lisp/ao_lisp_const.lisp
+++ b/src/lisp/ao_lisp_const.lisp
@@ -1 +1,4 @@
 cadr (lambda (l) (car (cdr l)))
+list (lexpr (l) l)
+1+ (lambda (x) (+ x 1))
+1- (lambda (x) (- x 1))
diff --git a/src/lisp/ao_lisp_error.c b/src/lisp/ao_lisp_error.c
new file mode 100644
index 00000000..ea8111d9
--- /dev/null
+++ b/src/lisp/ao_lisp_error.c
@@ -0,0 +1,29 @@
+/*
+ * Copyright © 2016 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include "ao_lisp.h"
+#include <stdarg.h>
+
+ao_poly
+ao_lisp_error(int error, char *format, ...)
+{
+	va_list	args;
+
+	ao_lisp_exception |= error;
+	va_start(args, format);
+	vprintf(format, args);
+	va_end(args);
+	printf("\n");
+	return AO_LISP_NIL;
+}
diff --git a/src/lisp/ao_lisp_eval.c b/src/lisp/ao_lisp_eval.c
index 6eef1f23..803f1e2e 100644
--- a/src/lisp/ao_lisp_eval.c
+++ b/src/lisp/ao_lisp_eval.c
@@ -14,32 +14,238 @@
 
 #include "ao_lisp.h"
 
-/*
- * Non-recursive eval
- *
- * Plan: walk actuals, construct formals
- *
- * stack >  save  > actuals > actual_1
- *           v         v
- *	   formals     .    > actual_2
- */
-
-static struct ao_lisp_cons	*stack;
-static struct ao_lisp_cons	*actuals;
-static struct ao_lisp_cons	*formals;
-static struct ao_lisp_cons	*formals_tail;
-static uint8_t been_here;
-
 #if 0
 #define DBG(...) printf(__VA_ARGS__)
-#define DBG_CONS(a)	ao_lisp_cons_print(a)
+#define DBG_CONS(a)	ao_lisp_cons_print(ao_lisp_cons_poly(a))
 #define DBG_POLY(a)	ao_lisp_poly_print(a)
+#define OFFSET(a)	((a) ? (int) ((uint8_t *) a - ao_lisp_pool) : -1)
 #else
 #define DBG(...)
 #define DBG_CONS(a)
 #define DBG_POLY(a)
 #endif
 
+struct ao_lisp_stack {
+	ao_poly			next;
+	ao_poly			actuals;
+	ao_poly			formals;
+	ao_poly			frame;
+	ao_poly			cond;
+};
+
+static struct ao_lisp_stack *
+ao_lisp_poly_stack(ao_poly p)
+{
+	return ao_lisp_ref(p);
+}
+
+static ao_poly
+ao_lisp_stack_poly(struct ao_lisp_stack *stack)
+{
+	return ao_lisp_poly(stack, AO_LISP_OTHER);
+}
+
+static int
+stack_size(void *addr)
+{
+	(void) addr;
+	return sizeof (struct ao_lisp_stack);
+}
+
+static void
+stack_mark(void *addr)
+{
+	struct ao_lisp_stack	*stack = addr;
+	for (;;) {
+		ao_lisp_poly_mark(stack->actuals);
+		ao_lisp_poly_mark(stack->formals);
+		ao_lisp_poly_mark(stack->frame);
+		ao_lisp_poly_mark(stack->cond);
+		stack = ao_lisp_poly_stack(stack->next);
+		if (ao_lisp_mark_memory(stack, sizeof (struct ao_lisp_stack)))
+			break;
+	}
+}
+
+static void
+stack_move(void *addr)
+{
+	struct ao_lisp_stack	*stack = addr;
+
+	for (;;) {
+		struct ao_lisp_stack *next;
+		stack->actuals = ao_lisp_poly_move(stack->actuals);
+		stack->formals = ao_lisp_poly_move(stack->formals);
+		stack->frame = ao_lisp_poly_move(stack->frame);
+		stack->cond = ao_lisp_poly_move(stack->cond);
+		next = ao_lisp_ref(stack->next);
+		next = ao_lisp_move_memory(next, sizeof (struct ao_lisp_stack));
+		stack->next = ao_lisp_stack_poly(next);
+		stack = next;
+	}
+}
+
+static const struct ao_lisp_type ao_lisp_stack_type = {
+	.size = stack_size,
+	.mark = stack_mark,
+	.move = stack_move
+};
+
+
+static struct ao_lisp_stack	*stack;
+static struct ao_lisp_cons	*actuals;
+static struct ao_lisp_cons	*formals;
+static struct ao_lisp_cons	*formals_tail;
+static struct ao_lisp_cons	*cond;
+struct ao_lisp_frame		*next_frame;
+static uint8_t been_here;
+
+ao_poly
+ao_lisp_set_cond(struct ao_lisp_cons *c)
+{
+	cond = c;
+	return AO_LISP_NIL;
+}
+
+static int
+ao_lisp_stack_push(void)
+{
+	struct ao_lisp_stack	*n = ao_lisp_alloc(sizeof (struct ao_lisp_stack));
+	if (!n)
+		return 0;
+	n->next = ao_lisp_stack_poly(stack);
+	n->actuals = ao_lisp_cons_poly(actuals);
+	n->formals = ao_lisp_cons_poly(formals);
+	n->cond = ao_lisp_cons_poly(cond);
+	n->frame = ao_lisp_frame_poly(ao_lisp_frame_current);
+	DBG("push frame %d\n", OFFSET(ao_lisp_frame_current));
+	stack = n;
+	return 1;
+}
+
+static void
+ao_lisp_stack_pop(void)
+{
+	actuals = ao_lisp_poly_cons(stack->actuals);
+	formals = ao_lisp_poly_cons(stack->formals);
+	cond = ao_lisp_poly_cons(stack->cond);
+	ao_lisp_frame_current = ao_lisp_poly_frame(stack->frame);
+	DBG("pop frame %d\n", OFFSET(ao_lisp_frame_current));
+	formals_tail = 0;
+
+	/* Recompute the tail of the formals list */
+	if (formals) {
+		struct ao_lisp_cons *formal;
+		for (formal = formals; formal->cdr != AO_LISP_NIL; formal = ao_lisp_poly_cons(formal->cdr));
+		formals_tail = formal;
+	}
+	stack = ao_lisp_poly_stack(stack->next);
+}
+
+static void
+ao_lisp_stack_clear(void)
+{
+	stack = 0;
+	actuals = formals = formals_tail = 0;
+	cond = 0;
+	ao_lisp_frame_current = 0;
+}
+
+
+static ao_poly
+func_type(ao_poly func)
+{
+	struct ao_lisp_cons	*cons;
+	struct ao_lisp_cons	*args;
+	int			f;
+
+	DBG("func type "); DBG_POLY(func); DBG("\n");
+	if (func == AO_LISP_NIL)
+		return ao_lisp_error(AO_LISP_INVALID, "func is nil");
+	if (ao_lisp_poly_type(func) != AO_LISP_CONS)
+		return ao_lisp_error(AO_LISP_INVALID, "func is not list");
+	cons = ao_lisp_poly_cons(func);
+	if (!ao_lisp_check_argc(_ao_lisp_atom_lambda, cons, 3, 3))
+		return AO_LISP_NIL;
+	if (!ao_lisp_check_argt(_ao_lisp_atom_lambda, cons, 0, AO_LISP_ATOM, 0))
+		return AO_LISP_NIL;
+	if (!ao_lisp_check_argt(_ao_lisp_atom_lambda, cons, 1, AO_LISP_CONS, 1))
+		return AO_LISP_NIL;
+	args = ao_lisp_poly_cons(ao_lisp_arg(cons, 1));
+	f = 0;
+	while (args) {
+		if (ao_lisp_poly_type(args->car) != AO_LISP_ATOM) {
+			return ao_lisp_error(ao_lisp_arg(cons, 0), "formal %d is not an atom", f);
+		}
+		args = ao_lisp_poly_cons(args->cdr);
+		f++;
+	}
+	return ao_lisp_arg(cons, 0);
+}
+
+static int
+ao_lisp_cons_length(struct ao_lisp_cons *cons)
+{
+	int	len = 0;
+	while (cons) {
+		len++;
+		cons = ao_lisp_poly_cons(cons->cdr);
+	}
+	return len;
+}
+
+static ao_poly
+ao_lisp_lambda(struct ao_lisp_cons *cons)
+{
+	ao_poly			type;
+	struct ao_lisp_cons	*lambda;
+	struct ao_lisp_cons	*args;
+	int			args_wanted;
+	int			args_provided;
+
+	lambda = ao_lisp_poly_cons(ao_lisp_arg(cons, 0));
+	DBG("lambda "); DBG_CONS(lambda); DBG("\n");
+	type = ao_lisp_arg(lambda, 0);
+	args = ao_lisp_poly_cons(ao_lisp_arg(lambda, 1));
+
+	args_wanted = ao_lisp_cons_length(args);
+
+	/* Create a frame to hold the variables
+	 */
+	if (type == _ao_lisp_atom_lambda)
+		args_provided = ao_lisp_cons_length(cons) - 1;
+	else
+		args_provided = 1;
+	if (args_wanted != args_provided)
+		return ao_lisp_error(AO_LISP_INVALID, "need %d args, not %d", args_wanted, args_provided);
+	next_frame = ao_lisp_frame_new(args_wanted, 0);
+	DBG("new frame %d\n", OFFSET(next_frame));
+	switch (type) {
+	case _ao_lisp_atom_lambda: {
+		int			f;
+		struct ao_lisp_cons	*vals = ao_lisp_poly_cons(cons->cdr);
+
+		for (f = 0; f < args_wanted; f++) {
+			next_frame->vals[f].atom = args->car;
+			next_frame->vals[f].val = vals->car;
+			args = ao_lisp_poly_cons(args->cdr);
+			vals = ao_lisp_poly_cons(vals->cdr);
+		}
+		break;
+	}
+	case _ao_lisp_atom_lexpr:
+	case _ao_lisp_atom_nlambda:
+		next_frame->vals[0].atom = args->car;
+		next_frame->vals[0].val = cons->cdr;
+		break;
+	case _ao_lisp_atom_macro:
+		next_frame->vals[0].atom = args->car;
+		next_frame->vals[0].val = ao_lisp_cons_poly(cons);
+		break;
+	}
+	return ao_lisp_arg(lambda, 2);
+}
+
 ao_poly
 ao_lisp_eval(ao_poly v)
 {
@@ -48,7 +254,7 @@ ao_lisp_eval(ao_poly v)
 
 	if (!been_here) {
 		been_here = 1;
-		ao_lisp_root_add(&ao_lisp_cons_type, &stack);
+		ao_lisp_root_add(&ao_lisp_stack_type, &stack);
 		ao_lisp_root_add(&ao_lisp_cons_type, &actuals);
 		ao_lisp_root_add(&ao_lisp_cons_type, &formals);
 		ao_lisp_root_add(&ao_lisp_cons_type, &formals_tail);
@@ -57,29 +263,43 @@ ao_lisp_eval(ao_poly v)
 	actuals = 0;
 	formals = 0;
 	formals_tail = 0;
+	cond = 0;
 	for (;;) {
 
 	restart:
+		if (cond) {
+			if (cond->car == AO_LISP_NIL) {
+				cond = AO_LISP_NIL;
+				v = AO_LISP_NIL;
+			} else {
+				if (ao_lisp_poly_type(cond->car) != AO_LISP_CONS) {
+					ao_lisp_error(AO_LISP_INVALID, "malformed cond");
+					goto bail;
+				}
+				v = ao_lisp_poly_cons(cond->car)->car;
+			}
+		}
+
 		/* Build stack frames for each list */
 		while (ao_lisp_poly_type(v) == AO_LISP_CONS) {
 			if (v == AO_LISP_NIL)
 				break;
 
-			/* Push existing frame on the stack */
-			if (cons++) {
-				struct ao_lisp_cons *frame;
+			/* Push existing bits on the stack */
+			if (cons++)
+				if (!ao_lisp_stack_push())
+					goto bail;
 
-				frame = ao_lisp_cons_cons(ao_lisp_cons_poly(actuals), formals);
-				stack = ao_lisp_cons_cons(ao_lisp_cons_poly(frame), stack);
-			}
 			actuals = ao_lisp_poly_cons(v);
 			formals = NULL;
 			formals_tail = NULL;
+			cond = NULL;
+
 			v = actuals->car;
 
-			DBG("start: stack"); DBG_CONS(stack); DBG("\n");
-			DBG("start: actuals"); DBG_CONS(actuals); DBG("\n");
-			DBG("start: formals"); DBG_CONS(formals); DBG("\n");
+//			DBG("start: stack"); DBG_CONS(stack); DBG("\n");
+//			DBG("start: actuals"); DBG_CONS(actuals); DBG("\n");
+//			DBG("start: formals"); DBG_CONS(formals); DBG("\n");
 		}
 
 		/* Evaluate primitive types */
@@ -95,19 +315,19 @@ ao_lisp_eval(ao_poly v)
 			break;
 		}
 
-		if (!cons)
-			break;
-
-		for (;;) {
+		while (cons) {
 			DBG("add formal: "); DBG_POLY(v); DBG("\n");
 
+			/* We've processed the first element of the list, go check
+			 * what kind of function we've got
+			 */
 			if (formals == NULL) {
 				if (ao_lisp_poly_type(v) == AO_LISP_BUILTIN) {
 					struct ao_lisp_builtin *b = ao_lisp_poly_builtin(v);
 					switch (b->args) {
 					case AO_LISP_NLAMBDA:
-						v = ao_lisp_func(b)(ao_lisp_poly_cons(actuals->cdr));
-						goto done_eval;
+						formals = actuals;
+						goto eval;
 
 					case AO_LISP_MACRO:
 						v = ao_lisp_func(b)(ao_lisp_poly_cons(actuals->cdr));
@@ -115,15 +335,28 @@ ao_lisp_eval(ao_poly v)
 						DBG(" -> "); DBG_POLY(v);
 						DBG("\n");
 						if (ao_lisp_poly_type(v) != AO_LISP_CONS) {
-							ao_lisp_exception |= AO_LISP_INVALID;
-							return AO_LISP_NIL;
+							ao_lisp_error(AO_LISP_INVALID, "macro didn't return list");
+							goto bail;
 						}
-
 						/* Reset frame to the new list */
 						actuals = ao_lisp_poly_cons(v);
 						v = actuals->car;
 						goto restart;
 					}
+				} else {
+					switch (func_type(v)) {
+					case _ao_lisp_atom_lambda:
+					case _ao_lisp_atom_lexpr:
+						break;
+					case _ao_lisp_atom_nlambda:
+						formals = actuals;
+						goto eval;
+					case _ao_lisp_atom_macro:
+						break;
+					default:
+						ao_lisp_error(AO_LISP_INVALID, "operator is not a function");
+						goto bail;
+					}
 				}
 			}
 
@@ -150,6 +383,8 @@ ao_lisp_eval(ao_poly v)
 
 			v = formals->car;
 
+		eval:
+
 			/* Evaluate the resulting list */
 			if (ao_lisp_poly_type(v) == AO_LISP_BUILTIN) {
 				struct ao_lisp_builtin *b = ao_lisp_poly_builtin(v);
@@ -161,41 +396,54 @@ ao_lisp_eval(ao_poly v)
 				DBG(" -> ");
 				DBG_POLY(v);
 				DBG ("\n");
+				if (ao_lisp_exception)
+					goto bail;
+
+				if (cond)
+					goto restart;
 			} else {
-				ao_lisp_exception |= AO_LISP_INVALID;
+				v = ao_lisp_lambda(formals);
+				if (ao_lisp_exception)
+					goto bail;
 			}
-			if (ao_lisp_exception)
-				return AO_LISP_NIL;
-		done_eval:
-			if (--cons) {
-				struct ao_lisp_cons	*frame;
-
-				/* Pop the previous frame off the stack */
-				frame = ao_lisp_poly_cons(stack->car);
-				actuals = ao_lisp_poly_cons(frame->car);
-				formals = ao_lisp_poly_cons(frame->cdr);
-				formals_tail = NULL;
-
-				/* Recompute the tail of the formals list */
-				if (formals) {
-					for (formal = formals; formal->cdr != AO_LISP_NIL; formal = ao_lisp_poly_cons(formal->cdr));
-					formals_tail = formal;
-				}
 
-				stack = ao_lisp_poly_cons(stack->cdr);
-				DBG("stack pop: stack"); DBG_CONS(stack); DBG("\n");
-				DBG("stack pop: actuals"); DBG_CONS(actuals); DBG("\n");
-				DBG("stack pop: formals"); DBG_CONS(formals); DBG("\n");
+			--cons;
+			if (cons) {
+				ao_lisp_stack_pop();
+//				DBG("stack pop: stack"); DBG_CONS(stack); DBG("\n");
+//				DBG("stack pop: actuals"); DBG_CONS(actuals); DBG("\n");
+//				DBG("stack pop: formals"); DBG_CONS(formals); DBG("\n");
 			} else {
 				actuals = 0;
 				formals = 0;
 				formals_tail = 0;
-				DBG("done func\n");
-				break;
+				ao_lisp_frame_current = 0;
+			}
+			if (next_frame) {
+				ao_lisp_frame_current = next_frame;
+				DBG("next frame %d\n", OFFSET(next_frame));
+				next_frame = 0;
+				goto restart;
+			}
+			if (cond) {
+				if (v) {
+					v = ao_lisp_poly_cons(cond->car)->cdr;
+					if (v != AO_LISP_NIL) {
+						v = ao_lisp_poly_cons(v)->car;
+						goto restart;
+					}
+				} else {
+					cond = ao_lisp_poly_cons(cond->cdr);
+					goto restart;
+				}
 			}
 		}
 		if (!cons)
 			break;
 	}
+	DBG("leaving frame at %d\n", OFFSET(ao_lisp_frame_current));
 	return v;
+bail:
+	ao_lisp_stack_clear();
+	return AO_LISP_NIL;
 }
diff --git a/src/lisp/ao_lisp_frame.c b/src/lisp/ao_lisp_frame.c
index 5aa50f6b..1853f6d7 100644
--- a/src/lisp/ao_lisp_frame.c
+++ b/src/lisp/ao_lisp_frame.c
@@ -95,7 +95,7 @@ const struct ao_lisp_type ao_lisp_frame_type = {
 	.move = frame_move
 };
 
-static ao_poly *
+ao_poly *
 ao_lisp_frame_ref(struct ao_lisp_frame *frame, ao_poly atom)
 {
 	int f;
diff --git a/src/lisp/ao_lisp_make_const.c b/src/lisp/ao_lisp_make_const.c
index 6b603979..9c2ea74c 100644
--- a/src/lisp/ao_lisp_make_const.c
+++ b/src/lisp/ao_lisp_make_const.c
@@ -39,6 +39,7 @@ struct builtin_func funcs[] = {
 	"quote",	AO_LISP_NLAMBDA,builtin_quote,
 	"set",		AO_LISP_LEXPR,	builtin_set,
 	"setq",		AO_LISP_MACRO,	builtin_setq,
+	"cond",		AO_LISP_NLAMBDA,builtin_cond,
 	"print",	AO_LISP_LEXPR,	builtin_print,
 	"+",		AO_LISP_LEXPR,	builtin_plus,
 	"-",		AO_LISP_LEXPR,	builtin_minus,
@@ -47,8 +48,25 @@ struct builtin_func funcs[] = {
 	"%",		AO_LISP_LEXPR,	builtin_mod
 };
 
+ao_poly
+ao_lisp_set_cond(struct ao_lisp_cons *c)
+{
+	(void) c;
+	return AO_LISP_NIL;
+}
+
 #define N_FUNC (sizeof funcs / sizeof funcs[0])
 
+/* Syntactic atoms */
+char *atoms[] = {
+	"lambda",
+	"nlambda",
+	"lexpr",
+	"macro"
+};
+
+#define N_ATOM (sizeof atoms / sizeof atoms[0])
+
 struct ao_lisp_frame	*globals;
 
 static int
@@ -65,9 +83,10 @@ is_atom(int offset)
 int
 main(int argc, char **argv)
 {
-	int	f, o;
+	int	f, o, i;
 	ao_poly	atom, val;
 	struct ao_lisp_atom	*a;
+	struct ao_lisp_builtin	*b;
 	int	in_atom;
 
 	printf("/*\n");
@@ -75,11 +94,15 @@ main(int argc, char **argv)
 	ao_lisp_root_add(&ao_lisp_frame_type, &globals);
 	globals = ao_lisp_frame_new(0, 0);
 	for (f = 0; f < N_FUNC; f++) {
-		struct ao_lisp_builtin	*b = ao_lisp_make_builtin(funcs[f].func, funcs[f].args);
-		struct ao_lisp_atom	*a = ao_lisp_atom_intern(funcs[f].name);
+		b = ao_lisp_make_builtin(funcs[f].func, funcs[f].args);
+		a = ao_lisp_atom_intern(funcs[f].name);
 		globals = ao_lisp_frame_add(globals, ao_lisp_atom_poly(a), ao_lisp_builtin_poly(b));
 	}
 
+	/* atoms for syntax */
+	for (i = 0; i < N_ATOM; i++)
+		(void) ao_lisp_atom_intern(atoms[i]);
+
 	/* boolean constants */
 	a = ao_lisp_atom_intern("nil");
 	globals = ao_lisp_frame_add(globals, ao_lisp_atom_poly(a), AO_LISP_NIL);
diff --git a/src/lisp/ao_lisp_rep.c b/src/lisp/ao_lisp_rep.c
index a1f9fa1f..d780186a 100644
--- a/src/lisp/ao_lisp_rep.c
+++ b/src/lisp/ao_lisp_rep.c
@@ -25,12 +25,6 @@ ao_lisp_read_eval_print(void)
 //		printf ("in: "); ao_lisp_poly_print(in); printf("\n");
 		out = ao_lisp_eval(in);
 		if (ao_lisp_exception) {
-			if (ao_lisp_exception & AO_LISP_OOM)
-				printf("out of memory\n");
-			if (ao_lisp_exception & AO_LISP_DIVIDE_BY_ZERO)
-				printf("divide by zero\n");
-			if (ao_lisp_exception & AO_LISP_INVALID)
-				printf("invalid operation\n");
 			ao_lisp_exception = 0;
 		} else {
 			ao_lisp_poly_print(out);
diff --git a/src/nucleao-32/Makefile b/src/nucleao-32/Makefile
index 1b7e0bb0..388e581c 100644
--- a/src/nucleao-32/Makefile
+++ b/src/nucleao-32/Makefile
@@ -46,6 +46,7 @@ ALTOS_SRC = \
 	ao_lisp_read.c \
 	ao_lisp_rep.c \
 	ao_lisp_frame.c \
+	ao_lisp_error.c \
 	ao_exti_stm.c
 
 PRODUCT=Nucleo-32
diff --git a/src/nucleao-32/ao_pins.h b/src/nucleao-32/ao_pins.h
index 76200176..65de89ed 100644
--- a/src/nucleao-32/ao_pins.h
+++ b/src/nucleao-32/ao_pins.h
@@ -24,6 +24,8 @@
 #define LED_PIN_GREEN	3
 #define AO_LED_GREEN	(1 << LED_PIN_GREEN)
 #define AO_LED_PANIC	AO_LED_GREEN
+#define AO_CMD_LEN	128
+#define AO_LISP_POOL	2048
 
 #define LEDS_AVAILABLE	(AO_LED_GREEN)
 
diff --git a/src/test/Makefile b/src/test/Makefile
index bd195161..8d617eea 100644
--- a/src/test/Makefile
+++ b/src/test/Makefile
@@ -93,7 +93,8 @@ ao_quaternion_test: ao_quaternion_test.c ao_quaternion.h
 
 AO_LISP_OBJS = ao_lisp_test.o ao_lisp_mem.o  ao_lisp_cons.o ao_lisp_string.o \
 	ao_lisp_atom.o ao_lisp_int.o ao_lisp_prim.o ao_lisp_eval.o ao_lisp_poly.o \
-	ao_lisp_builtin.o ao_lisp_read.o ao_lisp_rep.o ao_lisp_frame.o
+	ao_lisp_builtin.o ao_lisp_read.o ao_lisp_rep.o ao_lisp_frame.o \
+	ao_lisp_error.o
 
 ao_lisp_test: $(AO_LISP_OBJS)
 	cc $(CFLAGS) -o $@ $(AO_LISP_OBJS)
diff --git a/src/test/ao_lisp_test.c b/src/test/ao_lisp_test.c
index e303869f..8bc677da 100644
--- a/src/test/ao_lisp_test.c
+++ b/src/test/ao_lisp_test.c
@@ -15,15 +15,18 @@
 #include "ao_lisp.h"
 #include <stdio.h>
 
+#if 0
 static struct ao_lisp_cons	*list;
 static char			*string;
+#endif
 
 int
 main (int argc, char **argv)
 {
+#if 0
 	int			i, j;
-	struct ao_lisp_atom	*atom;
 
+	struct ao_lisp_atom	*atom;
 	ao_lisp_root_add(&ao_lisp_cons_type, (void **) &list);
 	ao_lisp_root_add(&ao_lisp_string_type, (void **) &string);
 
@@ -47,7 +50,8 @@ main (int argc, char **argv)
 		ao_lisp_poly_print(ao_lisp_atom_get(ao_lisp_atom_poly(atom)));
 		printf("\n");
 	}
-#if 1
+#endif
+#if 0
 	list = ao_lisp_cons_cons(ao_lisp_atom_poly(ao_lisp_atom_intern("+")),
 				 ao_lisp_cons_cons(ao_lisp_cons_poly(ao_lisp_cons_cons(ao_lisp_atom_poly(ao_lisp_atom_intern("+")),
 										       ao_lisp_cons_cons(ao_lisp_int_poly(3),
@@ -58,7 +62,8 @@ main (int argc, char **argv)
 	printf ("\n");
 	ao_lisp_poly_print(ao_lisp_eval(ao_lisp_cons_poly(list)));
 	printf ("\n");
-
+#endif
+#if 1
 	ao_lisp_read_eval_print();
 #endif
 }