X-Git-Url: https://git.gag.com/?p=fw%2Faltos;a=blobdiff_plain;f=src%2Flisp%2Fao_lisp_eval.c;h=3af567964deab8a4f87d13a26d13425e3508e901;hp=803f1e2ed11de17291b9725c9747f23d70fe0a65;hb=974717eb9dad105c9897ee24f953d98d57eaec77;hpb=77db0e8162cd01c2b42737b3d71b38cea942484f

diff --git a/src/lisp/ao_lisp_eval.c b/src/lisp/ao_lisp_eval.c
index 803f1e2e..3af56796 100644
--- a/src/lisp/ao_lisp_eval.c
+++ b/src/lisp/ao_lisp_eval.c
@@ -12,38 +12,11 @@
  * General Public License for more details.
  */
 
+#define DBG_EVAL 0
 #include "ao_lisp.h"
+#include <assert.h>
 
-#if 0
-#define DBG(...) printf(__VA_ARGS__)
-#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);
-}
+const struct ao_lisp_type ao_lisp_stack_type;
 
 static int
 stack_size(void *addr)
@@ -57,12 +30,13 @@ 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)))
+		ao_lisp_poly_mark(stack->sexprs, 0);
+		ao_lisp_poly_mark(stack->values, 0);
+		/* no need to mark values_tail */
+		ao_lisp_poly_mark(stack->frame, 0);
+		ao_lisp_poly_mark(stack->list, 0);
+		stack = ao_lisp_poly_stack(stack->prev);
+		if (ao_lisp_mark_memory(&ao_lisp_stack_type, stack))
 			break;
 	}
 }
@@ -72,378 +46,579 @@ 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;
+	while (stack) {
+		struct ao_lisp_stack	*prev;
+		int			ret;
+		(void) ao_lisp_poly_move(&stack->sexprs, 0);
+		(void) ao_lisp_poly_move(&stack->values, 0);
+		(void) ao_lisp_poly_move(&stack->values_tail, 0);
+		(void) ao_lisp_poly_move(&stack->frame, 0);
+		(void) ao_lisp_poly_move(&stack->list, 0);
+		prev = ao_lisp_poly_stack(stack->prev);
+		if (!prev)
+			break;
+		ret = ao_lisp_move_memory(&ao_lisp_stack_type, (void **) &prev);
+		if (prev != ao_lisp_poly_stack(stack->prev))
+			stack->prev = ao_lisp_stack_poly(prev);
+		if (ret)
+			break;
+		stack = prev;
 	}
 }
 
-static const struct ao_lisp_type ao_lisp_stack_type = {
+const struct ao_lisp_type ao_lisp_stack_type = {
 	.size = stack_size,
 	.mark = stack_mark,
-	.move = stack_move
+	.move = stack_move,
+	.name = "stack"
 };
 
+struct ao_lisp_stack		*ao_lisp_stack;
+ao_poly				ao_lisp_v;
 
-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;
+struct ao_lisp_stack		*ao_lisp_stack_free_list;
 
 ao_poly
 ao_lisp_set_cond(struct ao_lisp_cons *c)
 {
-	cond = c;
+	ao_lisp_stack->state = eval_cond;
+	ao_lisp_stack->sexprs = ao_lisp_cons_poly(c);
 	return AO_LISP_NIL;
 }
 
+static void
+ao_lisp_stack_reset(struct ao_lisp_stack *stack)
+{
+	stack->state = eval_sexpr;
+	stack->sexprs = AO_LISP_NIL;
+	stack->values = AO_LISP_NIL;
+	stack->values_tail = 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;
+	struct ao_lisp_stack	*stack;
+	if (ao_lisp_stack_free_list) {
+		stack = ao_lisp_stack_free_list;
+		ao_lisp_stack_free_list = ao_lisp_poly_stack(stack->prev);
+	} else {
+		stack = ao_lisp_alloc(sizeof (struct ao_lisp_stack));
+		if (!stack)
+			return 0;
+	}
+	stack->prev = ao_lisp_stack_poly(ao_lisp_stack);
+	stack->frame = ao_lisp_frame_poly(ao_lisp_frame_current);
+	stack->list = AO_LISP_NIL;
+	ao_lisp_stack = stack;
+	ao_lisp_stack_reset(stack);
+	DBGI("stack push\n");
+	DBG_FRAMES();
+	DBG_IN();
 	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);
+	ao_poly	prev;
+
+	if (!ao_lisp_stack)
+		return;
+	prev = ao_lisp_stack->prev;
+	ao_lisp_stack->prev = ao_lisp_stack_poly(ao_lisp_stack_free_list);
+	ao_lisp_stack_free_list = ao_lisp_stack;
+
+	ao_lisp_stack = ao_lisp_poly_stack(prev);
+	if (ao_lisp_stack)
+		ao_lisp_frame_current = ao_lisp_poly_frame(ao_lisp_stack->frame);
+	else
+		ao_lisp_frame_current = NULL;
+	DBG_OUT();
+	DBGI("stack pop\n");
+	DBG_FRAMES();
 }
 
 static void
 ao_lisp_stack_clear(void)
 {
-	stack = 0;
-	actuals = formals = formals_tail = 0;
-	cond = 0;
-	ao_lisp_frame_current = 0;
+	ao_lisp_stack = NULL;
+	ao_lisp_frame_current = NULL;
+	ao_lisp_v = AO_LISP_NIL;
 }
 
-
-static ao_poly
+static int
 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++;
+	switch (ao_lisp_poly_type(func)) {
+	case AO_LISP_BUILTIN:
+		return ao_lisp_poly_builtin(func)->args & AO_LISP_FUNC_MASK;
+	case AO_LISP_LAMBDA:
+		return ao_lisp_poly_lambda(func)->args;
+	default:
+		ao_lisp_error(AO_LISP_INVALID, "not a func");
+		return -1;
 	}
-	return ao_lisp_arg(cons, 0);
 }
 
+/*
+ * Flattened eval to avoid stack issues
+ */
+
+/*
+ * Evaluate an s-expression
+ *
+ * For a list, evaluate all of the elements and
+ * then execute the resulting function call.
+ *
+ * Each element of the list is evaluated in
+ * a clean stack context.
+ *
+ * The current stack state is set to 'formal' so that
+ * when the evaluation is complete, the value
+ * will get appended to the values list.
+ *
+ * For other types, compute the value directly.
+ */
+
 static int
-ao_lisp_cons_length(struct ao_lisp_cons *cons)
+ao_lisp_eval_sexpr(void)
 {
-	int	len = 0;
-	while (cons) {
-		len++;
-		cons = ao_lisp_poly_cons(cons->cdr);
+	DBGI("sexpr: "); DBG_POLY(ao_lisp_v); DBG("\n");
+	switch (ao_lisp_poly_type(ao_lisp_v)) {
+	case AO_LISP_CONS:
+		if (ao_lisp_v == AO_LISP_NIL) {
+			if (!ao_lisp_stack->values) {
+				/*
+				 * empty list evaluates to empty list
+				 */
+				ao_lisp_v = AO_LISP_NIL;
+				ao_lisp_stack->state = eval_val;
+			} else {
+				/*
+				 * done with arguments, go execute it
+				 */
+				ao_lisp_v = ao_lisp_poly_cons(ao_lisp_stack->values)->car;
+				ao_lisp_stack->state = eval_exec;
+			}
+		} else {
+			if (!ao_lisp_stack->values)
+				ao_lisp_stack->list = ao_lisp_v;
+			/*
+			 * Evaluate another argument and then switch
+			 * to 'formal' to add the value to the values
+			 * list
+			 */
+			ao_lisp_stack->sexprs = ao_lisp_v;
+			ao_lisp_stack->state = eval_formal;
+			if (!ao_lisp_stack_push())
+				return 0;
+			/*
+			 * push will reset the state to 'sexpr', which
+			 * will evaluate the expression
+			 */
+			ao_lisp_v = ao_lisp_poly_cons(ao_lisp_v)->car;
+		}
+		break;
+	case AO_LISP_ATOM:
+		DBGI("..frame "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");
+		ao_lisp_v = ao_lisp_atom_get(ao_lisp_v);
+		/* fall through */
+	case AO_LISP_INT:
+	case AO_LISP_STRING:
+	case AO_LISP_BUILTIN:
+	case AO_LISP_LAMBDA:
+		ao_lisp_stack->state = eval_val;
+		break;
 	}
-	return len;
+	DBGI(".. result "); DBG_POLY(ao_lisp_v); DBG("\n");
+	return 1;
 }
 
-static ao_poly
-ao_lisp_lambda(struct ao_lisp_cons *cons)
+/*
+ * A value has been computed.
+ *
+ * If the value was computed from a macro,
+ * then we want to reset the current context
+ * to evaluate the macro result again.
+ *
+ * If not a macro, then pop the stack.
+ * If the stack is empty, we're done.
+ * Otherwise, the stack will contain
+ * the next state.
+ */
+
+static int
+ao_lisp_eval_val(void)
 {
-	ao_poly			type;
-	struct ao_lisp_cons	*lambda;
-	struct ao_lisp_cons	*args;
-	int			args_wanted;
-	int			args_provided;
+	DBGI("val: "); DBG_POLY(ao_lisp_v); DBG("\n");
+	/*
+	 * Value computed, pop the stack
+	 * to figure out what to do with the value
+	 */
+	ao_lisp_stack_pop();
+	DBGI("..state %d\n", ao_lisp_stack ? ao_lisp_stack->state : -1);
+	return 1;
+}
 
-	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));
+/*
+ * A formal has been computed.
+ *
+ * If this is the first formal, then check to see if we've got a
+ * lamda/lexpr or macro/nlambda.
+ *
+ * For lambda/lexpr, go compute another formal.  This will terminate
+ * when the sexpr state sees nil.
+ *
+ * For macro/nlambda, we're done, so move the sexprs into the values
+ * and go execute it.
+ *
+ * Macros have an additional step of saving a stack frame holding the
+ * macro value execution context, which then gets the result of the
+ * macro to run
+ */
 
-	args_wanted = ao_lisp_cons_length(args);
+static int
+ao_lisp_eval_formal(void)
+{
+	ao_poly			formal;
+	struct ao_lisp_stack	*prev;
 
-	/* 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);
+	DBGI("formal: "); DBG_POLY(ao_lisp_v); DBG("\n");
+
+	/* Check what kind of function we've got */
+	if (!ao_lisp_stack->values) {
+		switch (func_type(ao_lisp_v)) {
+		case AO_LISP_FUNC_LAMBDA:
+		case AO_LISP_FUNC_LEXPR:
+			DBGI(".. lambda or lexpr\n");
+			break;
+		case AO_LISP_FUNC_MACRO:
+			/* Evaluate the result once more */
+			ao_lisp_stack->state = eval_macro;
+			if (!ao_lisp_stack_push())
+				return 0;
+
+			/* After the function returns, take that
+			 * value and re-evaluate it
+			 */
+			prev = ao_lisp_poly_stack(ao_lisp_stack->prev);
+			ao_lisp_stack->state = eval_sexpr;
+			ao_lisp_stack->sexprs = prev->sexprs;
+
+			DBGI(".. start macro\n");
+			DBGI(".. sexprs       "); DBG_POLY(ao_lisp_stack->sexprs); DBG("\n");
+			DBGI(".. values       "); DBG_POLY(ao_lisp_stack->values); DBG("\n");
+			DBG_FRAMES();
+
+			/* fall through ... */
+		case AO_LISP_FUNC_NLAMBDA:
+			DBGI(".. nlambda or macro\n");
+
+			/* use the raw sexprs as values */
+			ao_lisp_stack->values = ao_lisp_stack->sexprs;
+			ao_lisp_stack->values_tail = AO_LISP_NIL;
+			ao_lisp_stack->state = eval_exec;
+
+			/* ready to execute now */
+			return 1;
+		case -1:
+			return 0;
 		}
-		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)
-{
-	struct ao_lisp_cons	*formal;
-	int			cons = 0;
-
-	if (!been_here) {
-		been_here = 1;
-		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);
-	}
-	stack = 0;
-	actuals = 0;
-	formals = 0;
-	formals_tail = 0;
-	cond = 0;
-	for (;;) {
+	/* Append formal to list of values */
+	formal = ao_lisp_cons_poly(ao_lisp_cons_cons(ao_lisp_v, NULL));
+	if (!formal)
+		return 0;
 
-	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;
-			}
-		}
+	if (ao_lisp_stack->values_tail)
+		ao_lisp_poly_cons(ao_lisp_stack->values_tail)->cdr = formal;
+	else
+		ao_lisp_stack->values = formal;
+	ao_lisp_stack->values_tail = formal;
 
-		/* Build stack frames for each list */
-		while (ao_lisp_poly_type(v) == AO_LISP_CONS) {
-			if (v == AO_LISP_NIL)
-				break;
+	DBGI(".. values "); DBG_POLY(ao_lisp_stack->values); DBG("\n");
 
-			/* Push existing bits on the stack */
-			if (cons++)
-				if (!ao_lisp_stack_push())
-					goto bail;
+	/*
+	 * Step to the next argument, if this is last, then
+	 * 'sexpr' will end up switching to 'exec'
+	 */
+	ao_lisp_v = ao_lisp_poly_cons(ao_lisp_stack->sexprs)->cdr;
 
-			actuals = ao_lisp_poly_cons(v);
-			formals = NULL;
-			formals_tail = NULL;
-			cond = NULL;
+	ao_lisp_stack->state = eval_sexpr;
 
-			v = actuals->car;
+	DBGI(".. "); DBG_POLY(ao_lisp_v); DBG("\n");
+	return 1;
+}
 
-//			DBG("start: stack"); DBG_CONS(stack); DBG("\n");
-//			DBG("start: actuals"); DBG_CONS(actuals); DBG("\n");
-//			DBG("start: formals"); DBG_CONS(formals); DBG("\n");
-		}
+/*
+ * Start executing a function call
+ *
+ * Most builtins are easy, just call the function.
+ * 'cond' is magic; it sticks the list of clauses
+ * in 'sexprs' and switches to 'cond' state. That
+ * bit of magic is done in ao_lisp_set_cond.
+ *
+ * Lambdas build a new frame to hold the locals and
+ * then re-use the current stack context to evaluate
+ * the s-expression from the lambda.
+ */
 
-		/* Evaluate primitive types */
+static int
+ao_lisp_eval_exec(void)
+{
+	ao_poly v;
+	struct ao_lisp_builtin	*builtin;
+
+	DBGI("exec: "); DBG_POLY(ao_lisp_v); DBG(" values "); DBG_POLY(ao_lisp_stack->values); DBG ("\n");
+	ao_lisp_stack->sexprs = AO_LISP_NIL;
+	switch (ao_lisp_poly_type(ao_lisp_v)) {
+	case AO_LISP_BUILTIN:
+		ao_lisp_stack->state = eval_val;
+		builtin = ao_lisp_poly_builtin(ao_lisp_v);
+		v = ao_lisp_func(builtin) (
+			ao_lisp_poly_cons(ao_lisp_poly_cons(ao_lisp_stack->values)->cdr));
+		DBG_DO(if (!ao_lisp_exception && ao_lisp_poly_builtin(ao_lisp_v)->func == builtin_set) {
+				struct ao_lisp_cons *cons = ao_lisp_poly_cons(ao_lisp_stack->values);
+				ao_poly atom = ao_lisp_arg(cons, 1);
+				ao_poly val = ao_lisp_arg(cons, 2);
+				DBGI("set "); DBG_POLY(atom); DBG(" = "); DBG_POLY(val); DBG("\n");
+			});
+		builtin = ao_lisp_poly_builtin(ao_lisp_v);
+		if (builtin->args & AO_LISP_FUNC_FREE_ARGS)
+			ao_lisp_cons_free(ao_lisp_poly_cons(ao_lisp_stack->values));
+
+		ao_lisp_v = v;
+		DBGI(".. result "); DBG_POLY(ao_lisp_v); DBG ("\n");
+		DBGI(".. frame "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");
+		break;
+	case AO_LISP_LAMBDA:
+		ao_lisp_stack->state = eval_sexpr;
+		DBGI(".. frame "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");
+		ao_lisp_v = ao_lisp_lambda_eval();
+		DBGI(".. sexpr "); DBG_POLY(ao_lisp_v); DBG("\n");
+		DBGI(".. frame "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");
+		break;
+	}
+	ao_lisp_stack->values = AO_LISP_NIL;
+	ao_lisp_stack->values_tail = AO_LISP_NIL;
+	return 1;
+}
 
-		DBG ("actual: "); DBG_POLY(v); DBG("\n");
+/*
+ * Start evaluating the next cond clause
+ *
+ * If the list of clauses is empty, then
+ * the result of the cond is nil.
+ *
+ * Otherwise, set the current stack state to 'cond_test' and create a
+ * new stack context to evaluate the test s-expression. Once that's
+ * complete, we'll land in 'cond_test' to finish the clause.
+ */
+static int
+ao_lisp_eval_cond(void)
+{
+	DBGI("cond: "); DBG_POLY(ao_lisp_stack->sexprs); DBG("\n");
+	DBGI(".. frame "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");
+	DBGI(".. saved frame "); DBG_POLY(ao_lisp_stack->frame); DBG("\n");
+	if (!ao_lisp_stack->sexprs) {
+		ao_lisp_v = AO_LISP_NIL;
+		ao_lisp_stack->state = eval_val;
+	} else {
+		ao_lisp_v = ao_lisp_poly_cons(ao_lisp_stack->sexprs)->car;
+		if (!ao_lisp_v || ao_lisp_poly_type(ao_lisp_v) != AO_LISP_CONS) {
+			ao_lisp_error(AO_LISP_INVALID, "invalid cond clause");
+			return 0;
+		}
+		ao_lisp_v = ao_lisp_poly_cons(ao_lisp_v)->car;
+		ao_lisp_stack->state = eval_cond_test;
+		if (!ao_lisp_stack_push())
+			return 0;
+		ao_lisp_stack->state = eval_sexpr;
+	}
+	return 1;
+}
 
-		switch (ao_lisp_poly_type(v)) {
-		case AO_LISP_INT:
-		case AO_LISP_STRING:
-			break;
-		case AO_LISP_ATOM:
-			v = ao_lisp_atom_get(v);
-			break;
+/*
+ * Finish a cond clause.
+ *
+ * Check the value from the test expression, if
+ * non-nil, then set up to evaluate the value expression.
+ *
+ * Otherwise, step to the next clause and go back to the 'cond'
+ * state
+ */
+static int
+ao_lisp_eval_cond_test(void)
+{
+	DBGI("cond_test: "); DBG_POLY(ao_lisp_v); DBG(" sexprs "); DBG_POLY(ao_lisp_stack->sexprs); DBG("\n");
+	DBGI(".. frame "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");
+	DBGI(".. saved frame "); DBG_POLY(ao_lisp_stack->frame); DBG("\n");
+	if (ao_lisp_v) {
+		struct ao_lisp_cons *car = ao_lisp_poly_cons(ao_lisp_poly_cons(ao_lisp_stack->sexprs)->car);
+		struct ao_lisp_cons *c = ao_lisp_poly_cons(car->cdr);
+
+		if (c) {
+			ao_lisp_stack->state = eval_sexpr;
+			ao_lisp_v = c->car;
+		} else
+			ao_lisp_stack->state = eval_val;
+	} else {
+		ao_lisp_stack->sexprs = ao_lisp_poly_cons(ao_lisp_stack->sexprs)->cdr;
+		DBGI("next cond: "); DBG_POLY(ao_lisp_stack->sexprs); DBG("\n");
+		ao_lisp_stack->state = eval_cond;
+	}
+	return 1;
+}
+
+/*
+ * Evaluate a list of sexprs, returning the value from the last one.
+ *
+ * ao_lisp_progn records the list in stack->sexprs, so we just need to
+ * walk that list. Set ao_lisp_v to the car of the list and jump to
+ * eval_sexpr. When that's done, it will land in eval_val. For all but
+ * the last, leave a stack frame with eval_progn set so that we come
+ * back here. For the last, don't add a stack frame so that we can
+ * just continue on.
+ */
+static int
+ao_lisp_eval_progn(void)
+{
+	DBGI("progn: "); DBG_POLY(ao_lisp_v); DBG(" sexprs "); DBG_POLY(ao_lisp_stack->sexprs); DBG("\n");
+	DBGI(".. frame "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");
+	DBGI(".. saved frame "); DBG_POLY(ao_lisp_stack->frame); DBG("\n");
+
+	if (!ao_lisp_stack->sexprs) {
+		ao_lisp_v = AO_LISP_NIL;
+		ao_lisp_stack->state = eval_val;
+	} else {
+		ao_lisp_v = ao_lisp_poly_cons(ao_lisp_stack->sexprs)->car;
+		ao_lisp_stack->sexprs = ao_lisp_poly_cons(ao_lisp_stack->sexprs)->cdr;
+		if (ao_lisp_stack->sexprs) {
+			ao_lisp_stack->state = eval_progn;
+			if (!ao_lisp_stack_push())
+				return 0;
 		}
+		ao_lisp_stack->state = eval_sexpr;
+	}
+	return 1;
+}
 
-		while (cons) {
-			DBG("add formal: "); DBG_POLY(v); DBG("\n");
+/*
+ * Conditionally execute a list of sexprs while the first is true
+ */
+static int
+ao_lisp_eval_while(void)
+{
+	DBGI("while: "); DBG_POLY(ao_lisp_stack->sexprs); DBG("\n");
+	DBGI(".. frame "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");
+	DBGI(".. saved frame "); DBG_POLY(ao_lisp_stack->frame); DBG("\n");
+
+	if (!ao_lisp_stack->sexprs) {
+		ao_lisp_v = AO_LISP_NIL;
+		ao_lisp_stack->state = eval_val;
+	} else {
+		ao_lisp_v = ao_lisp_poly_cons(ao_lisp_stack->sexprs)->car;
+		ao_lisp_stack->state = eval_while_test;
+		if (!ao_lisp_stack_push())
+			return 0;
+		ao_lisp_stack->state = eval_sexpr;
+	}
+	return 1;
+}
 
-			/* 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:
-						formals = actuals;
-						goto eval;
-
-					case AO_LISP_MACRO:
-						v = ao_lisp_func(b)(ao_lisp_poly_cons(actuals->cdr));
-						DBG("macro "); DBG_POLY(ao_lisp_cons_poly(actuals));
-						DBG(" -> "); DBG_POLY(v);
-						DBG("\n");
-						if (ao_lisp_poly_type(v) != AO_LISP_CONS) {
-							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;
-					}
-				}
-			}
+/*
+ * Check the while condition, terminate the loop if nil. Otherwise keep going
+ */
+static int
+ao_lisp_eval_while_test(void)
+{
+	DBGI("while_test: "); DBG_POLY(ao_lisp_v); DBG(" sexprs "); DBG_POLY(ao_lisp_stack->sexprs); DBG("\n");
+	DBGI(".. frame "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");
+	DBGI(".. saved frame "); DBG_POLY(ao_lisp_stack->frame); DBG("\n");
+
+	if (ao_lisp_v) {
+		ao_lisp_v = ao_lisp_poly_cons(ao_lisp_stack->sexprs)->cdr;
+		if (ao_lisp_v)
+			ao_lisp_v = ao_lisp_poly_cons(ao_lisp_v)->car;
+		ao_lisp_stack->state = eval_while;
+		if (!ao_lisp_stack_push())
+			return 0;
+	}
+	else
+		ao_lisp_stack->state = eval_val;
+	return 1;
+}
 
-			formal = ao_lisp_cons_cons(v, NULL);
-			if (formals_tail)
-				formals_tail->cdr = ao_lisp_cons_poly(formal);
-			else
-				formals = formal;
-			formals_tail = formal;
-			actuals = ao_lisp_poly_cons(actuals->cdr);
-
-			DBG("formals: ");
-			DBG_CONS(formals);
-			DBG("\n");
-			DBG("actuals: ");
-			DBG_CONS(actuals);
-			DBG("\n");
-
-			/* Process all of the arguments */
-			if (actuals) {
-				v = actuals->car;
-				break;
-			}
+/*
+ * Replace the original sexpr with the macro expansion, then
+ * execute that
+ */
+static int
+ao_lisp_eval_macro(void)
+{
+	DBGI("macro: "); DBG_POLY(ao_lisp_v); DBG(" sexprs "); DBG_POLY(ao_lisp_stack->sexprs); DBG("\n");
+
+	if (ao_lisp_poly_type(ao_lisp_v) == AO_LISP_CONS) {
+		*ao_lisp_poly_cons(ao_lisp_stack->sexprs) = *ao_lisp_poly_cons(ao_lisp_v);
+		ao_lisp_v = ao_lisp_stack->sexprs;
+		DBGI("sexprs rewritten to: "); DBG_POLY(ao_lisp_v); DBG("\n");
+	}
+	ao_lisp_stack->sexprs = AO_LISP_NIL;
+	ao_lisp_stack->state = eval_sexpr;
+	return 1;
+}
 
-			v = formals->car;
+static int (*const evals[])(void) = {
+	[eval_sexpr] = ao_lisp_eval_sexpr,
+	[eval_val] = ao_lisp_eval_val,
+	[eval_formal] = ao_lisp_eval_formal,
+	[eval_exec] = ao_lisp_eval_exec,
+	[eval_cond] = ao_lisp_eval_cond,
+	[eval_cond_test] = ao_lisp_eval_cond_test,
+	[eval_progn] = ao_lisp_eval_progn,
+	[eval_while] = ao_lisp_eval_while,
+	[eval_while_test] = ao_lisp_eval_while_test,
+	[eval_macro] = ao_lisp_eval_macro,
+};
 
-		eval:
+/*
+ * Called at restore time to reset all execution state
+ */
 
-			/* Evaluate the resulting list */
-			if (ao_lisp_poly_type(v) == AO_LISP_BUILTIN) {
-				struct ao_lisp_builtin *b = ao_lisp_poly_builtin(v);
+void
+ao_lisp_eval_clear_globals(void)
+{
+	ao_lisp_stack = NULL;
+	ao_lisp_frame_current = NULL;
+	ao_lisp_v = AO_LISP_NIL;
+}
 
-				v = ao_lisp_func(b) (ao_lisp_poly_cons(formals->cdr));
+int
+ao_lisp_eval_restart(void)
+{
+	return ao_lisp_stack_push();
+}
 
-				DBG ("eval: ");
-				DBG_CONS(formals);
-				DBG(" -> ");
-				DBG_POLY(v);
-				DBG ("\n");
-				if (ao_lisp_exception)
-					goto bail;
+ao_poly
+ao_lisp_eval(ao_poly _v)
+{
+	ao_lisp_v = _v;
 
-				if (cond)
-					goto restart;
-			} else {
-				v = ao_lisp_lambda(formals);
-				if (ao_lisp_exception)
-					goto bail;
-			}
+	if (!ao_lisp_stack_push())
+		return AO_LISP_NIL;
 
-			--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;
-				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;
-				}
-			}
+	while (ao_lisp_stack) {
+		if (!(*evals[ao_lisp_stack->state])() || ao_lisp_exception) {
+			ao_lisp_stack_clear();
+			return AO_LISP_NIL;
 		}
-		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;
+	DBG_DO(if (ao_lisp_frame_current) {DBGI("frame left as "); DBG_POLY(ao_lisp_frame_poly(ao_lisp_frame_current)); DBG("\n");});
+	ao_lisp_frame_current = NULL;
+	return ao_lisp_v;
 }