Add minimal abstract machine module

lib/CMakeLists.txt

@@ -1,4 +1,5 @@
 add_library(imp
+  am.c
   memory_stream.c
   store.c
   token.c

lib/am.c

@@ -0,0 +1,22 @@
+#include "am.h"
+
+#include <assert.h>
+#include <string.h>
+
+void am_init(am_t *am)
+{
+	memset(am, 0, sizeof(am_t));
+	am->sp = am->stack + AM_STACK_SIZE - 1;
+}
+
+void am_push(am_t *am)
+{
+	assert(am->sp >= am->stack);
+	*am->sp-- = am->expr;
+}
+
+void am_pop(am_t *am)
+{
+	assert(am->sp < am->stack + AM_STACK_SIZE - 1);
+	am->expr = *++am->sp;
+}

lib/include/am.h

@@ -0,0 +1,17 @@
+#ifndef AM_H
+#define AM_H
+
+#include "expr.h"
+
+#define AM_STACK_SIZE 128U
+
+typedef struct {
+	expr_t *expr;
+	expr_t **sp, *stack[AM_STACK_SIZE];
+} am_t;
+
+void am_init(am_t *am);
+void am_push(am_t *am);
+void am_pop(am_t *am);
+
+#endif