add circuitpython code

1 files changed, 1256 insertions, 0 deletions

diff --git a/circuitpython/py/parse.c b/circuitpython/py/parse.c
new file mode 100644
index 0000000..dee662b
--- /dev/null
+++ b/circuitpython/py/parse.c
@@ -0,0 +1,1256 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * SPDX-FileCopyrightText: Copyright (c) 2013-2017 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <unistd.h> // for ssize_t
+#include <assert.h>
+#include <string.h>
+
+#include "py/lexer.h"
+#include "py/parse.h"
+#include "py/parsenum.h"
+#include "py/runtime.h"
+#include "py/objint.h"
+#include "py/objstr.h"
+#include "py/builtin.h"
+
+#include "supervisor/shared/translate.h"
+
+#if MICROPY_ENABLE_COMPILER
+
+#define RULE_ACT_ARG_MASK       (0x0f)
+#define RULE_ACT_KIND_MASK      (0x30)
+#define RULE_ACT_ALLOW_IDENT    (0x40)
+#define RULE_ACT_ADD_BLANK      (0x80)
+#define RULE_ACT_OR             (0x10)
+#define RULE_ACT_AND            (0x20)
+#define RULE_ACT_LIST           (0x30)
+
+#define RULE_ARG_KIND_MASK      (0xf000)
+#define RULE_ARG_ARG_MASK       (0x0fff)
+#define RULE_ARG_TOK            (0x1000)
+#define RULE_ARG_RULE           (0x2000)
+#define RULE_ARG_OPT_RULE       (0x3000)
+
+// *FORMAT-OFF*
+
+enum {
+// define rules with a compile function
+#define DEF_RULE(rule, comp, kind, ...) RULE_##rule,
+#define DEF_RULE_NC(rule, kind, ...)
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+    RULE_const_object, // special node for a constant, generic Python object
+
+// define rules without a compile function
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) RULE_##rule,
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+};
+
+// Define an array of actions corresponding to each rule
+STATIC const uint8_t rule_act_table[] = {
+#define or(n)                   (RULE_ACT_OR | n)
+#define and(n)                  (RULE_ACT_AND | n)
+#define and_ident(n)            (RULE_ACT_AND | n | RULE_ACT_ALLOW_IDENT)
+#define and_blank(n)            (RULE_ACT_AND | n | RULE_ACT_ADD_BLANK)
+#define one_or_more             (RULE_ACT_LIST | 2)
+#define list                    (RULE_ACT_LIST | 1)
+#define list_with_end           (RULE_ACT_LIST | 3)
+
+#define DEF_RULE(rule, comp, kind, ...) kind,
+#define DEF_RULE_NC(rule, kind, ...)
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+
+    0, // RULE_const_object
+
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) kind,
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+
+#undef or
+#undef and
+#undef and_ident
+#undef and_blank
+#undef one_or_more
+#undef list
+#undef list_with_end
+};
+
+// Define the argument data for each rule, as a combined array
+STATIC const uint16_t rule_arg_combined_table[] = {
+#define tok(t)                  (RULE_ARG_TOK | MP_TOKEN_##t)
+#define rule(r)                 (RULE_ARG_RULE | RULE_##r)
+#define opt_rule(r)             (RULE_ARG_OPT_RULE | RULE_##r)
+
+#define DEF_RULE(rule, comp, kind, ...) __VA_ARGS__,
+#define DEF_RULE_NC(rule, kind, ...)
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...)  __VA_ARGS__,
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+
+#undef tok
+#undef rule
+#undef opt_rule
+};
+
+// Macro to create a list of N identifiers where N is the number of variable arguments to the macro
+#define RULE_EXPAND(x) x
+#define RULE_PADDING(rule, ...) RULE_PADDING2(rule, __VA_ARGS__, RULE_PADDING_IDS(rule))
+#define RULE_PADDING2(rule, ...) RULE_EXPAND(RULE_PADDING3(rule, __VA_ARGS__))
+#define RULE_PADDING3(rule, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, ...) __VA_ARGS__
+#define RULE_PADDING_IDS(r) PAD13_##r, PAD12_##r, PAD11_##r, PAD10_##r, PAD9_##r, PAD8_##r, PAD7_##r, PAD6_##r, PAD5_##r, PAD4_##r, PAD3_##r, PAD2_##r, PAD1_##r,
+
+// Use an enum to create constants specifying how much room a rule takes in rule_arg_combined_table
+enum {
+#define DEF_RULE(rule, comp, kind, ...) RULE_PADDING(rule, __VA_ARGS__)
+#define DEF_RULE_NC(rule, kind, ...)
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) RULE_PADDING(rule, __VA_ARGS__)
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+};
+
+// Macro to compute the start of a rule in rule_arg_combined_table
+#define RULE_ARG_OFFSET(rule, ...) RULE_ARG_OFFSET2(rule, __VA_ARGS__, RULE_ARG_OFFSET_IDS(rule))
+#define RULE_ARG_OFFSET2(rule, ...) RULE_EXPAND(RULE_ARG_OFFSET3(rule, __VA_ARGS__))
+#define RULE_ARG_OFFSET3(rule, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, ...) _14
+#define RULE_ARG_OFFSET_IDS(r) PAD13_##r, PAD12_##r, PAD11_##r, PAD10_##r, PAD9_##r, PAD8_##r, PAD7_##r, PAD6_##r, PAD5_##r, PAD4_##r, PAD3_##r, PAD2_##r, PAD1_##r, PAD0_##r,
+
+// Use the above enum values to create a table of offsets for each rule's arg
+// data, which indexes rule_arg_combined_table.  The offsets require 9 bits of
+// storage but only the lower 8 bits are stored here.  The 9th bit is computed
+// in get_rule_arg using the FIRST_RULE_WITH_OFFSET_ABOVE_255 constant.
+STATIC const uint8_t rule_arg_offset_table[] = {
+#define DEF_RULE(rule, comp, kind, ...) RULE_ARG_OFFSET(rule, __VA_ARGS__) & 0xff,
+#define DEF_RULE_NC(rule, kind, ...)
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+    0, // RULE_const_object
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) RULE_ARG_OFFSET(rule, __VA_ARGS__) & 0xff,
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+};
+
+// Define a constant that's used to determine the 9th bit of the values in rule_arg_offset_table
+static const size_t FIRST_RULE_WITH_OFFSET_ABOVE_255 =
+#define DEF_RULE(rule, comp, kind, ...) RULE_ARG_OFFSET(rule, __VA_ARGS__) >= 0x100 ? RULE_##rule :
+#define DEF_RULE_NC(rule, kind, ...)
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) RULE_ARG_OFFSET(rule, __VA_ARGS__) >= 0x100 ? RULE_##rule :
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+    0;
+
+#if MICROPY_DEBUG_PARSE_RULE_NAME
+// Define an array of rule names corresponding to each rule
+STATIC const char *const rule_name_table[] = {
+#define DEF_RULE(rule, comp, kind, ...) #rule,
+#define DEF_RULE_NC(rule, kind, ...)
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+    "", // RULE_const_object
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) #rule,
+    #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+};
+#endif
+
+// *FORMAT-ON*
+
+typedef struct _rule_stack_t {
+    size_t src_line : (8 * sizeof(size_t) - 8); // maximum bits storing source line number
+    size_t rule_id : 8; // this must be large enough to fit largest rule number
+    size_t arg_i; // this dictates the maximum nodes in a "list" of things
+} rule_stack_t;
+
+typedef struct _mp_parse_chunk_t {
+    size_t alloc;
+    union {
+        size_t used;
+        struct _mp_parse_chunk_t *next;
+    } union_;
+    byte data[];
+} mp_parse_chunk_t;
+
+typedef struct _parser_t {
+    size_t rule_stack_alloc;
+    size_t rule_stack_top;
+    rule_stack_t *rule_stack;
+
+    size_t result_stack_alloc;
+    size_t result_stack_top;
+    mp_parse_node_t *result_stack;
+
+    mp_lexer_t *lexer;
+
+    mp_parse_tree_t tree;
+    mp_parse_chunk_t *cur_chunk;
+
+    #if MICROPY_COMP_CONST
+    mp_map_t consts;
+    #endif
+} parser_t;
+
+STATIC const uint16_t *get_rule_arg(uint8_t r_id) {
+    size_t off = rule_arg_offset_table[r_id];
+    if (r_id >= FIRST_RULE_WITH_OFFSET_ABOVE_255) {
+        off |= 0x100;
+    }
+    return &rule_arg_combined_table[off];
+}
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wcast-align"
+
+STATIC void *parser_alloc(parser_t *parser, size_t num_bytes) {
+    // use a custom memory allocator to store parse nodes sequentially in large chunks
+
+    mp_parse_chunk_t *chunk = parser->cur_chunk;
+
+    if (chunk != NULL && chunk->union_.used + num_bytes > chunk->alloc) {
+        // not enough room at end of previously allocated chunk so try to grow
+        mp_parse_chunk_t *new_data = (mp_parse_chunk_t *)m_renew_maybe(byte, chunk,
+            sizeof(mp_parse_chunk_t) + chunk->alloc,
+            sizeof(mp_parse_chunk_t) + chunk->alloc + num_bytes, false);
+        if (new_data == NULL) {
+            // could not grow existing memory; shrink it to fit previous
+            (void)m_renew_maybe(byte, chunk, sizeof(mp_parse_chunk_t) + chunk->alloc,
+                sizeof(mp_parse_chunk_t) + chunk->union_.used, false);
+            chunk->alloc = chunk->union_.used;
+            chunk->union_.next = parser->tree.chunk;
+            parser->tree.chunk = chunk;
+            chunk = NULL;
+        } else {
+            // could grow existing memory
+            chunk->alloc += num_bytes;
+        }
+    }
+
+    if (chunk == NULL) {
+        // no previous chunk, allocate a new chunk
+        size_t alloc = MICROPY_ALLOC_PARSE_CHUNK_INIT;
+        if (alloc < num_bytes) {
+            alloc = num_bytes;
+        }
+        chunk = (mp_parse_chunk_t *)m_new(byte, sizeof(mp_parse_chunk_t) + alloc);
+        chunk->alloc = alloc;
+        chunk->union_.used = 0;
+        parser->cur_chunk = chunk;
+    }
+
+    byte *ret = chunk->data + chunk->union_.used;
+    chunk->union_.used += num_bytes;
+    return ret;
+}
+#pragma GCC diagnostic pop
+
+STATIC void push_rule(parser_t *parser, size_t src_line, uint8_t rule_id, size_t arg_i) {
+    if (parser->rule_stack_top >= parser->rule_stack_alloc) {
+        rule_stack_t *rs = m_renew(rule_stack_t, parser->rule_stack, parser->rule_stack_alloc, parser->rule_stack_alloc + MICROPY_ALLOC_PARSE_RULE_INC);
+        parser->rule_stack = rs;
+        parser->rule_stack_alloc += MICROPY_ALLOC_PARSE_RULE_INC;
+    }
+    rule_stack_t *rs = &parser->rule_stack[parser->rule_stack_top++];
+    rs->src_line = src_line;
+    rs->rule_id = rule_id;
+    rs->arg_i = arg_i;
+}
+
+STATIC void push_rule_from_arg(parser_t *parser, size_t arg) {
+    assert((arg & RULE_ARG_KIND_MASK) == RULE_ARG_RULE || (arg & RULE_ARG_KIND_MASK) == RULE_ARG_OPT_RULE);
+    size_t rule_id = arg & RULE_ARG_ARG_MASK;
+    push_rule(parser, parser->lexer->tok_line, rule_id, 0);
+}
+
+STATIC uint8_t pop_rule(parser_t *parser, size_t *arg_i, size_t *src_line) {
+    parser->rule_stack_top -= 1;
+    uint8_t rule_id = parser->rule_stack[parser->rule_stack_top].rule_id;
+    *arg_i = parser->rule_stack[parser->rule_stack_top].arg_i;
+    *src_line = parser->rule_stack[parser->rule_stack_top].src_line;
+    return rule_id;
+}
+
+bool mp_parse_node_is_const_false(mp_parse_node_t pn) {
+    return MP_PARSE_NODE_IS_TOKEN_KIND(pn, MP_TOKEN_KW_FALSE)
+           || (MP_PARSE_NODE_IS_SMALL_INT(pn) && MP_PARSE_NODE_LEAF_SMALL_INT(pn) == 0);
+}
+
+bool mp_parse_node_is_const_true(mp_parse_node_t pn) {
+    return MP_PARSE_NODE_IS_TOKEN_KIND(pn, MP_TOKEN_KW_TRUE)
+           || (MP_PARSE_NODE_IS_SMALL_INT(pn) && MP_PARSE_NODE_LEAF_SMALL_INT(pn) != 0);
+}
+
+bool mp_parse_node_get_int_maybe(mp_parse_node_t pn, mp_obj_t *o) {
+    if (MP_PARSE_NODE_IS_SMALL_INT(pn)) {
+        *o = MP_OBJ_NEW_SMALL_INT(MP_PARSE_NODE_LEAF_SMALL_INT(pn));
+        return true;
+    } else if (MP_PARSE_NODE_IS_STRUCT_KIND(pn, RULE_const_object)) {
+        mp_parse_node_struct_t *pns = (mp_parse_node_struct_t *)pn;
+        #if MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_D
+        // nodes are 32-bit pointers, but need to extract 64-bit object
+        *o = (uint64_t)pns->nodes[0] | ((uint64_t)pns->nodes[1] << 32);
+        #else
+        *o = (mp_obj_t)pns->nodes[0];
+        #endif
+        return mp_obj_is_int(*o);
+    } else {
+        return false;
+    }
+}
+
+size_t mp_parse_node_extract_list(mp_parse_node_t *pn, size_t pn_kind, mp_parse_node_t **nodes) {
+    if (MP_PARSE_NODE_IS_NULL(*pn)) {
+        *nodes = NULL;
+        return 0;
+    } else if (MP_PARSE_NODE_IS_LEAF(*pn)) {
+        *nodes = pn;
+        return 1;
+    } else {
+        mp_parse_node_struct_t *pns = (mp_parse_node_struct_t *)(*pn);
+        if (MP_PARSE_NODE_STRUCT_KIND(pns) != pn_kind) {
+            *nodes = pn;
+            return 1;
+        } else {
+            *nodes = pns->nodes;
+            return MP_PARSE_NODE_STRUCT_NUM_NODES(pns);
+        }
+    }
+}
+
+#if MICROPY_DEBUG_PRINTERS
+void mp_parse_node_print(const mp_print_t *print, mp_parse_node_t pn, size_t indent) {
+    if (MP_PARSE_NODE_IS_STRUCT(pn)) {
+        mp_printf(print, "[% 4d] ", (int)((mp_parse_node_struct_t *)pn)->source_line);
+    } else {
+        mp_printf(print, "       ");
+    }
+    for (size_t i = 0; i < indent; i++) {
+        mp_printf(print, " ");
+    }
+    if (MP_PARSE_NODE_IS_NULL(pn)) {
+        mp_printf(print, "NULL\n");
+    } else if (MP_PARSE_NODE_IS_SMALL_INT(pn)) {
+        mp_int_t arg = MP_PARSE_NODE_LEAF_SMALL_INT(pn);
+        mp_printf(print, "int(" INT_FMT ")\n", arg);
+    } else if (MP_PARSE_NODE_IS_LEAF(pn)) {
+        uintptr_t arg = MP_PARSE_NODE_LEAF_ARG(pn);
+        switch (MP_PARSE_NODE_LEAF_KIND(pn)) {
+            case MP_PARSE_NODE_ID:
+                mp_printf(print, "id(%s)\n", qstr_str(arg));
+                break;
+            case MP_PARSE_NODE_STRING:
+                mp_printf(print, "str(%s)\n", qstr_str(arg));
+                break;
+            case MP_PARSE_NODE_BYTES:
+                mp_printf(print, "bytes(%s)\n", qstr_str(arg));
+                break;
+            default:
+                assert(MP_PARSE_NODE_LEAF_KIND(pn) == MP_PARSE_NODE_TOKEN);
+                mp_printf(print, "tok(%u)\n", (uint)arg);
+                break;
+        }
+    } else {
+        // node must be a mp_parse_node_struct_t
+        mp_parse_node_struct_t *pns = (mp_parse_node_struct_t *)pn;
+        if (MP_PARSE_NODE_STRUCT_KIND(pns) == RULE_const_object) {
+            #if MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_D
+            mp_printf(print, "literal const(%016llx)\n", (uint64_t)pns->nodes[0] | ((uint64_t)pns->nodes[1] << 32));
+            #else
+            mp_printf(print, "literal const(%p)\n", (mp_obj_t)pns->nodes[0]);
+            #endif
+        } else {
+            size_t n = MP_PARSE_NODE_STRUCT_NUM_NODES(pns);
+            #if MICROPY_DEBUG_PARSE_RULE_NAME
+            mp_printf(print, "%s(%u) (n=%u)\n", rule_name_table[MP_PARSE_NODE_STRUCT_KIND(pns)], (uint)MP_PARSE_NODE_STRUCT_KIND(pns), (uint)n);
+            #else
+            mp_printf(print, "rule(%u) (n=%u)\n", (uint)MP_PARSE_NODE_STRUCT_KIND(pns), (uint)n);
+            #endif
+            for (size_t i = 0; i < n; i++) {
+                mp_parse_node_print(print, pns->nodes[i], indent + 2);
+            }
+        }
+    }
+}
+#endif // MICROPY_DEBUG_PRINTERS
+
+/*
+STATIC void result_stack_show(const mp_print_t *print, parser_t *parser) {
+    mp_printf(print, "result stack, most recent first\n");
+    for (ssize_t i = parser->result_stack_top - 1; i >= 0; i--) {
+        mp_parse_node_print(print, parser->result_stack[i], 0);
+    }
+}
+*/
+
+STATIC mp_parse_node_t pop_result(parser_t *parser) {
+    assert(parser->result_stack_top > 0);
+    return parser->result_stack[--parser->result_stack_top];
+}
+
+STATIC mp_parse_node_t peek_result(parser_t *parser, size_t pos) {
+    assert(parser->result_stack_top > pos);
+    return parser->result_stack[parser->result_stack_top - 1 - pos];
+}
+
+STATIC void push_result_node(parser_t *parser, mp_parse_node_t pn) {
+    if (parser->result_stack_top >= parser->result_stack_alloc) {
+        mp_parse_node_t *stack = m_renew(mp_parse_node_t, parser->result_stack, parser->result_stack_alloc, parser->result_stack_alloc + MICROPY_ALLOC_PARSE_RESULT_INC);
+        parser->result_stack = stack;
+        parser->result_stack_alloc += MICROPY_ALLOC_PARSE_RESULT_INC;
+    }
+    parser->result_stack[parser->result_stack_top++] = pn;
+}
+
+STATIC mp_parse_node_t make_node_const_object(parser_t *parser, size_t src_line, mp_obj_t obj) {
+    mp_parse_node_struct_t *pn = parser_alloc(parser, sizeof(mp_parse_node_struct_t) + sizeof(mp_obj_t));
+    pn->source_line = src_line;
+    #if MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_D
+    // nodes are 32-bit pointers, but need to store 64-bit object
+    pn->kind_num_nodes = RULE_const_object | (2 << 8);
+    pn->nodes[0] = (uint64_t)obj;
+    pn->nodes[1] = (uint64_t)obj >> 32;
+    #else
+    pn->kind_num_nodes = RULE_const_object | (1 << 8);
+    pn->nodes[0] = (uintptr_t)obj;
+    #endif
+    return (mp_parse_node_t)pn;
+}
+
+STATIC mp_parse_node_t mp_parse_node_new_small_int_checked(parser_t *parser, mp_obj_t o_val) {
+    (void)parser;
+    mp_int_t val = MP_OBJ_SMALL_INT_VALUE(o_val);
+    #if MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_D
+    // A parse node is only 32-bits and the small-int value must fit in 31-bits
+    if (((val ^ (val << 1)) & 0xffffffff80000000) != 0) {
+        return make_node_const_object(parser, 0, o_val);
+    }
+    #endif
+    return mp_parse_node_new_small_int(val);
+}
+
+STATIC void push_result_token(parser_t *parser, uint8_t rule_id) {
+    mp_parse_node_t pn;
+    mp_lexer_t *lex = parser->lexer;
+    if (lex->tok_kind == MP_TOKEN_NAME) {
+        qstr id = qstr_from_strn(lex->vstr.buf, lex->vstr.len);
+        #if MICROPY_COMP_CONST
+        // if name is a standalone identifier, look it up in the table of dynamic constants
+        mp_map_elem_t *elem;
+        if (rule_id == RULE_atom
+            && (elem = mp_map_lookup(&parser->consts, MP_OBJ_NEW_QSTR(id), MP_MAP_LOOKUP)) != NULL) {
+            if (mp_obj_is_small_int(elem->value)) {
+                pn = mp_parse_node_new_small_int_checked(parser, elem->value);
+            } else {
+                pn = make_node_const_object(parser, lex->tok_line, elem->value);
+            }
+        } else {
+            pn = mp_parse_node_new_leaf(MP_PARSE_NODE_ID, id);
+        }
+        #else
+        (void)rule_id;
+        pn = mp_parse_node_new_leaf(MP_PARSE_NODE_ID, id);
+        #endif
+    } else if (lex->tok_kind == MP_TOKEN_INTEGER) {
+        mp_obj_t o = mp_parse_num_integer(lex->vstr.buf, lex->vstr.len, 0, lex);
+        if (mp_obj_is_small_int(o)) {
+            pn = mp_parse_node_new_small_int_checked(parser, o);
+        } else {
+            pn = make_node_const_object(parser, lex->tok_line, o);
+        }
+    } else if (lex->tok_kind == MP_TOKEN_FLOAT_OR_IMAG) {
+        mp_obj_t o = mp_parse_num_decimal(lex->vstr.buf, lex->vstr.len, true, false, lex);
+        pn = make_node_const_object(parser, lex->tok_line, o);
+    } else if (lex->tok_kind == MP_TOKEN_STRING || lex->tok_kind == MP_TOKEN_BYTES) {
+        // Don't automatically intern all strings/bytes.  doc strings (which are usually large)
+        // will be discarded by the compiler, and so we shouldn't intern them.
+        qstr qst = MP_QSTRnull;
+        if (lex->vstr.len <= MICROPY_ALLOC_PARSE_INTERN_STRING_LEN) {
+            // intern short strings
+            qst = qstr_from_strn(lex->vstr.buf, lex->vstr.len);
+        } else {
+            // check if this string is already interned
+            qst = qstr_find_strn(lex->vstr.buf, lex->vstr.len);
+        }
+        if (qst != MP_QSTRnull) {
+            // qstr exists, make a leaf node
+            pn = mp_parse_node_new_leaf(lex->tok_kind == MP_TOKEN_STRING ? MP_PARSE_NODE_STRING : MP_PARSE_NODE_BYTES, qst);
+        } else {
+            // not interned, make a node holding a pointer to the string/bytes object
+            mp_obj_t o = mp_obj_new_str_copy(
+                lex->tok_kind == MP_TOKEN_STRING ? &mp_type_str : &mp_type_bytes,
+                (const byte *)lex->vstr.buf, lex->vstr.len);
+            pn = make_node_const_object(parser, lex->tok_line, o);
+        }
+    } else {
+        pn = mp_parse_node_new_leaf(MP_PARSE_NODE_TOKEN, lex->tok_kind);
+    }
+    push_result_node(parser, pn);
+}
+
+#if MICROPY_COMP_MODULE_CONST
+STATIC const mp_rom_map_elem_t mp_constants_table[] = {
+    #if MICROPY_PY_UERRNO
+    { MP_ROM_QSTR(MP_QSTR_errno), MP_ROM_PTR(&mp_module_uerrno) },
+    #endif
+    #if MICROPY_PY_UCTYPES
+    { MP_ROM_QSTR(MP_QSTR_uctypes), MP_ROM_PTR(&mp_module_uctypes) },
+    #endif
+    // Extra constants as defined by a port
+    MICROPY_PORT_CONSTANTS
+};
+STATIC MP_DEFINE_CONST_MAP(mp_constants_map, mp_constants_table);
+#endif
+
+STATIC void push_result_rule(parser_t *parser, size_t src_line, uint8_t rule_id, size_t num_args);
+
+#if MICROPY_COMP_CONST_FOLDING
+STATIC bool fold_logical_constants(parser_t *parser, uint8_t rule_id, size_t *num_args) {
+    if (rule_id == RULE_or_test
+        || rule_id == RULE_and_test) {
+        // folding for binary logical ops: or and
+        size_t copy_to = *num_args;
+        for (size_t i = copy_to; i > 0;) {
+            mp_parse_node_t pn = peek_result(parser, --i);
+            parser->result_stack[parser->result_stack_top - copy_to] = pn;
+            if (i == 0) {
+                // always need to keep the last value
+                break;
+            }
+            if (rule_id == RULE_or_test) {
+                if (mp_parse_node_is_const_true(pn)) {
+                    //
+                    break;
+                } else if (!mp_parse_node_is_const_false(pn)) {
+                    copy_to -= 1;
+                }
+            } else {
+                // RULE_and_test
+                if (mp_parse_node_is_const_false(pn)) {
+                    break;
+                } else if (!mp_parse_node_is_const_true(pn)) {
+                    copy_to -= 1;
+                }
+            }
+        }
+        copy_to -= 1; // copy_to now contains number of args to pop
+
+        // pop and discard all the short-circuited expressions
+        for (size_t i = 0; i < copy_to; ++i) {
+            pop_result(parser);
+        }
+        *num_args -= copy_to;
+
+        // we did a complete folding if there's only 1 arg left
+        return *num_args == 1;
+
+    } else if (rule_id == RULE_not_test_2) {
+        // folding for unary logical op: not
+        mp_parse_node_t pn = peek_result(parser, 0);
+        if (mp_parse_node_is_const_false(pn)) {
+            pn = mp_parse_node_new_leaf(MP_PARSE_NODE_TOKEN, MP_TOKEN_KW_TRUE);
+        } else if (mp_parse_node_is_const_true(pn)) {
+            pn = mp_parse_node_new_leaf(MP_PARSE_NODE_TOKEN, MP_TOKEN_KW_FALSE);
+        } else {
+            return false;
+        }
+        pop_result(parser);
+        push_result_node(parser, pn);
+        return true;
+    }
+
+    return false;
+}
+
+STATIC bool fold_constants(parser_t *parser, uint8_t rule_id, size_t num_args) {
+    // this code does folding of arbitrary integer expressions, eg 1 + 2 * 3 + 4
+    // it does not do partial folding, eg 1 + 2 + x -> 3 + x
+
+    mp_obj_t arg0;
+    if (rule_id == RULE_expr
+        || rule_id == RULE_xor_expr
+        || rule_id == RULE_and_expr
+        || rule_id == RULE_power) {
+        // folding for binary ops: | ^ & **
+        mp_parse_node_t pn = peek_result(parser, num_args - 1);
+        if (!mp_parse_node_get_int_maybe(pn, &arg0)) {
+            return false;
+        }
+        mp_binary_op_t op;
+        if (rule_id == RULE_expr) {
+            op = MP_BINARY_OP_OR;
+        } else if (rule_id == RULE_xor_expr) {
+            op = MP_BINARY_OP_XOR;
+        } else if (rule_id == RULE_and_expr) {
+            op = MP_BINARY_OP_AND;
+        } else {
+            op = MP_BINARY_OP_POWER;
+        }
+        for (ssize_t i = num_args - 2; i >= 0; --i) {
+            pn = peek_result(parser, i);
+            mp_obj_t arg1;
+            if (!mp_parse_node_get_int_maybe(pn, &arg1)) {
+                return false;
+            }
+            if (op == MP_BINARY_OP_POWER && mp_obj_int_sign(arg1) < 0) {
+                // ** can't have negative rhs
+                return false;
+            }
+            arg0 = mp_binary_op(op, arg0, arg1);
+        }
+    } else if (rule_id == RULE_shift_expr
+               || rule_id == RULE_arith_expr
+               || rule_id == RULE_term) {
+        // folding for binary ops: << >> + - * @ / % //
+        mp_parse_node_t pn = peek_result(parser, num_args - 1);
+        if (!mp_parse_node_get_int_maybe(pn, &arg0)) {
+            return false;
+        }
+        for (ssize_t i = num_args - 2; i >= 1; i -= 2) {
+            pn = peek_result(parser, i - 1);
+            mp_obj_t arg1;
+            if (!mp_parse_node_get_int_maybe(pn, &arg1)) {
+                return false;
+            }
+            mp_token_kind_t tok = MP_PARSE_NODE_LEAF_ARG(peek_result(parser, i));
+            if (tok == MP_TOKEN_OP_AT || tok == MP_TOKEN_OP_SLASH) {
+                // Can't fold @ or /
+                return false;
+            }
+            mp_binary_op_t op = MP_BINARY_OP_LSHIFT + (tok - MP_TOKEN_OP_DBL_LESS);
+            int rhs_sign = mp_obj_int_sign(arg1);
+            if (op <= MP_BINARY_OP_RSHIFT) {
+                // << and >> can't have negative rhs
+                if (rhs_sign < 0) {
+                    return false;
+                }
+            } else if (op >= MP_BINARY_OP_FLOOR_DIVIDE) {
+                // % and // can't have zero rhs
+                if (rhs_sign == 0) {
+                    return false;
+                }
+            }
+            arg0 = mp_binary_op(op, arg0, arg1);
+        }
+    } else if (rule_id == RULE_factor_2) {
+        // folding for unary ops: + - ~
+        mp_parse_node_t pn = peek_result(parser, 0);
+        if (!mp_parse_node_get_int_maybe(pn, &arg0)) {
+            return false;
+        }
+        mp_token_kind_t tok = MP_PARSE_NODE_LEAF_ARG(peek_result(parser, 1));
+        mp_unary_op_t op;
+        if (tok == MP_TOKEN_OP_TILDE) {
+            op = MP_UNARY_OP_INVERT;
+        } else {
+            assert(tok == MP_TOKEN_OP_PLUS || tok == MP_TOKEN_OP_MINUS); // should be
+            op = MP_UNARY_OP_POSITIVE + (tok - MP_TOKEN_OP_PLUS);
+        }
+        arg0 = mp_unary_op(op, arg0);
+
+    #if MICROPY_COMP_CONST
+    } else if (rule_id == RULE_expr_stmt) {
+        mp_parse_node_t pn1 = peek_result(parser, 0);
+        if (!MP_PARSE_NODE_IS_NULL(pn1)
+            && !(MP_PARSE_NODE_IS_STRUCT_KIND(pn1, RULE_expr_stmt_augassign)
+                 || MP_PARSE_NODE_IS_STRUCT_KIND(pn1, RULE_expr_stmt_assign_list))) {
+            // this node is of the form <x> = <y>
+            mp_parse_node_t pn0 = peek_result(parser, 1);
+            if (MP_PARSE_NODE_IS_ID(pn0)
+                && MP_PARSE_NODE_IS_STRUCT_KIND(pn1, RULE_atom_expr_normal)
+                && MP_PARSE_NODE_IS_ID(((mp_parse_node_struct_t *)pn1)->nodes[0])
+                && MP_PARSE_NODE_LEAF_ARG(((mp_parse_node_struct_t *)pn1)->nodes[0]) == MP_QSTR_const
+                && MP_PARSE_NODE_IS_STRUCT_KIND(((mp_parse_node_struct_t *)pn1)->nodes[1], RULE_trailer_paren)
+                ) {
+                // code to assign dynamic constants: id = const(value)
+
+                // get the id
+                qstr id = MP_PARSE_NODE_LEAF_ARG(pn0);
+
+                // get the value
+                mp_parse_node_t pn_value = ((mp_parse_node_struct_t *)((mp_parse_node_struct_t *)pn1)->nodes[1])->nodes[0];
+                mp_obj_t value;
+                if (!mp_parse_node_get_int_maybe(pn_value, &value)) {
+                    mp_obj_t exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
+                        MP_ERROR_TEXT("constant must be an integer"));
+                    mp_obj_exception_add_traceback(exc, parser->lexer->source_name,
+                        ((mp_parse_node_struct_t *)pn1)->source_line, MP_QSTRnull);
+                    nlr_raise(exc);
+                }
+
+                // store the value in the table of dynamic constants
+                mp_map_elem_t *elem = mp_map_lookup(&parser->consts, MP_OBJ_NEW_QSTR(id), MP_MAP_LOOKUP_ADD_IF_NOT_FOUND);
+                assert(elem->value == MP_OBJ_NULL);
+                elem->value = value;
+
+                // If the constant starts with an underscore then treat it as a private
+                // variable and don't emit any code to store the value to the id.
+                if (qstr_str(id)[0] == '_') {
+                    pop_result(parser); // pop const(value)
+                    pop_result(parser); // pop id
+                    push_result_rule(parser, 0, RULE_pass_stmt, 0); // replace with "pass"
+                    return true;
+                }
+
+                // replace const(value) with value
+                pop_result(parser);
+                push_result_node(parser, pn_value);
+
+                // finished folding this assignment, but we still want it to be part of the tree
+                return false;
+            }
+        }
+        return false;
+    #endif
+
+    #if MICROPY_COMP_MODULE_CONST
+    } else if (rule_id == RULE_atom_expr_normal) {
+        mp_parse_node_t pn0 = peek_result(parser, 1);
+        mp_parse_node_t pn1 = peek_result(parser, 0);
+        if (!(MP_PARSE_NODE_IS_ID(pn0)
+              && MP_PARSE_NODE_IS_STRUCT_KIND(pn1, RULE_trailer_period))) {
+            return false;
+        }
+        // id1.id2
+        // look it up in constant table, see if it can be replaced with an integer
+        mp_parse_node_struct_t *pns1 = (mp_parse_node_struct_t *)pn1;
+        assert(MP_PARSE_NODE_IS_ID(pns1->nodes[0]));
+        qstr q_base = MP_PARSE_NODE_LEAF_ARG(pn0);
+        qstr q_attr = MP_PARSE_NODE_LEAF_ARG(pns1->nodes[0]);
+        mp_map_elem_t *elem = mp_map_lookup((mp_map_t *)&mp_constants_map, MP_OBJ_NEW_QSTR(q_base), MP_MAP_LOOKUP);
+        if (elem == NULL) {
+            return false;
+        }
+        mp_obj_t dest[2];
+        mp_load_method_maybe(elem->value, q_attr, dest);
+        if (!(dest[0] != MP_OBJ_NULL && mp_obj_is_int(dest[0]) && dest[1] == MP_OBJ_NULL)) {
+            return false;
+        }
+        arg0 = dest[0];
+    #endif
+
+    } else {
+        return false;
+    }
+
+    // success folding this rule
+
+    for (size_t i = num_args; i > 0; i--) {
+        pop_result(parser);
+    }
+    if (mp_obj_is_small_int(arg0)) {
+        push_result_node(parser, mp_parse_node_new_small_int_checked(parser, arg0));
+    } else {
+        // TODO reuse memory for parse node struct?
+        push_result_node(parser, make_node_const_object(parser, 0, arg0));
+    }
+
+    return true;
+}
+#endif
+
+STATIC void push_result_rule(parser_t *parser, size_t src_line, uint8_t rule_id, size_t num_args) {
+    // Simplify and optimise certain rules, to reduce memory usage and simplify the compiler.
+    if (rule_id == RULE_atom_paren) {
+        // Remove parenthesis around a single expression if possible.
+        // This atom_paren rule always has a single argument, and after this
+        // optimisation that argument is either NULL or testlist_comp.
+        mp_parse_node_t pn = peek_result(parser, 0);
+        if (MP_PARSE_NODE_IS_NULL(pn)) {
+            // need to keep parenthesis for ()
+        } else if (MP_PARSE_NODE_IS_STRUCT_KIND(pn, RULE_testlist_comp)) {
+            // need to keep parenthesis for (a, b, ...)
+        } else {
+            // parenthesis around a single expression, so it's just the expression
+            return;
+        }
+    } else if (rule_id == RULE_testlist_comp) {
+        // The testlist_comp rule can be the sole argument to either atom_parent
+        // or atom_bracket, for (...) and [...] respectively.
+        assert(num_args == 2);
+        mp_parse_node_t pn = peek_result(parser, 0);
+        if (MP_PARSE_NODE_IS_STRUCT(pn)) {
+            mp_parse_node_struct_t *pns = (mp_parse_node_struct_t *)pn;
+            if (MP_PARSE_NODE_STRUCT_KIND(pns) == RULE_testlist_comp_3b) {
+                // tuple of one item, with trailing comma
+                pop_result(parser);
+                --num_args;
+            } else if (MP_PARSE_NODE_STRUCT_KIND(pns) == RULE_testlist_comp_3c) {
+                // tuple of many items, convert testlist_comp_3c to testlist_comp
+                pop_result(parser);
+                assert(pn == peek_result(parser, 0));
+                pns->kind_num_nodes = rule_id | MP_PARSE_NODE_STRUCT_NUM_NODES(pns) << 8;
+                return;
+            } else if (MP_PARSE_NODE_STRUCT_KIND(pns) == RULE_comp_for) {
+                // generator expression
+            } else {
+                // tuple with 2 items
+            }
+        } else {
+            // tuple with 2 items
+        }
+    } else if (rule_id == RULE_testlist_comp_3c) {
+        // steal first arg of outer testlist_comp rule
+        ++num_args;
+    }
+
+    #if MICROPY_COMP_CONST_FOLDING
+    if (fold_logical_constants(parser, rule_id, &num_args)) {
+        // we folded this rule so return straight away
+        return;
+    }
+    if (fold_constants(parser, rule_id, num_args)) {
+        // we folded this rule so return straight away
+        return;
+    }
+    #endif
+
+    mp_parse_node_struct_t *pn = parser_alloc(parser, sizeof(mp_parse_node_struct_t) + sizeof(mp_parse_node_t) * num_args);
+    pn->source_line = src_line;
+    pn->kind_num_nodes = (rule_id & 0xff) | (num_args << 8);
+    for (size_t i = num_args; i > 0; i--) {
+        pn->nodes[i - 1] = pop_result(parser);
+    }
+    if (rule_id == RULE_testlist_comp_3c) {
+        // need to push something non-null to replace stolen first arg of testlist_comp
+        push_result_node(parser, (mp_parse_node_t)pn);
+    }
+    push_result_node(parser, (mp_parse_node_t)pn);
+}
+
+mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
+
+    // initialise parser and allocate memory for its stacks
+
+    parser_t parser;
+
+    parser.rule_stack_alloc = MICROPY_ALLOC_PARSE_RULE_INIT;
+    parser.rule_stack_top = 0;
+    parser.rule_stack = NULL;
+    while (parser.rule_stack_alloc > 1) {
+        parser.rule_stack = m_new_maybe(rule_stack_t, parser.rule_stack_alloc);
+        if (parser.rule_stack != NULL) {
+            break;
+        } else {
+            parser.rule_stack_alloc /= 2;
+        }
+    }
+
+    parser.result_stack_alloc = MICROPY_ALLOC_PARSE_RESULT_INIT;
+    parser.result_stack_top = 0;
+    parser.result_stack = NULL;
+    while (parser.result_stack_alloc > 1) {
+        parser.result_stack = m_new_maybe(mp_parse_node_t, parser.result_stack_alloc);
+        if (parser.result_stack != NULL) {
+            break;
+        } else {
+            parser.result_stack_alloc /= 2;
+        }
+    }
+    if (parser.rule_stack == NULL || parser.result_stack == NULL) {
+        mp_raise_msg(&mp_type_MemoryError, MP_ERROR_TEXT("Unable to init parser"));
+    }
+
+    parser.lexer = lex;
+
+    parser.tree.chunk = NULL;
+    parser.cur_chunk = NULL;
+
+    #if MICROPY_COMP_CONST
+    mp_map_init(&parser.consts, 0);
+    #endif
+
+    // work out the top-level rule to use, and push it on the stack
+    size_t top_level_rule;
+    switch (input_kind) {
+        case MP_PARSE_SINGLE_INPUT:
+            top_level_rule = RULE_single_input;
+            break;
+        case MP_PARSE_EVAL_INPUT:
+            top_level_rule = RULE_eval_input;
+            break;
+        default:
+            top_level_rule = RULE_file_input;
+    }
+    push_rule(&parser, lex->tok_line, top_level_rule, 0);
+
+    // parse!
+
+    bool backtrack = false;
+
+    for (;;) {
+    next_rule:
+        if (parser.rule_stack_top == 0) {
+            break;
+        }
+
+        // Pop the next rule to process it
+        size_t i; // state for the current rule
+        size_t rule_src_line; // source line for the first token matched by the current rule
+        uint8_t rule_id = pop_rule(&parser, &i, &rule_src_line);
+        uint8_t rule_act = rule_act_table[rule_id];
+        const uint16_t *rule_arg = get_rule_arg(rule_id);
+        size_t n = rule_act & RULE_ACT_ARG_MASK;
+
+        #if 0
+        // debugging
+        printf("depth=" UINT_FMT " ", parser.rule_stack_top);
+        for (int j = 0; j < parser.rule_stack_top; ++j) {
+            printf(" ");
+        }
+        printf("%s n=" UINT_FMT " i=" UINT_FMT " bt=%d\n", rule_name_table[rule_id], n, i, backtrack);
+        #endif
+
+        switch (rule_act & RULE_ACT_KIND_MASK) {
+            case RULE_ACT_OR:
+                if (i > 0 && !backtrack) {
+                    goto next_rule;
+                } else {
+                    backtrack = false;
+                }
+                for (; i < n; ++i) {
+                    // printf("--> inside for @L924\n");
+                    uint16_t kind = rule_arg[i] & RULE_ARG_KIND_MASK;
+                    if (kind == RULE_ARG_TOK) {
+                        if (lex->tok_kind == (rule_arg[i] & RULE_ARG_ARG_MASK)) {
+                            push_result_token(&parser, rule_id);
+                            mp_lexer_to_next(lex);
+                            goto next_rule;
+                        }
+                    } else {
+                        assert(kind == RULE_ARG_RULE);
+                        if (i + 1 < n) {
+                            push_rule(&parser, rule_src_line, rule_id, i + 1); // save this or-rule
+                        }
+                        push_rule_from_arg(&parser, rule_arg[i]); // push child of or-rule
+                        goto next_rule;
+                    }
+                }
+                backtrack = true;
+                break;
+
+            case RULE_ACT_AND: {
+
+                // failed, backtrack if we can, else syntax error
+                if (backtrack) {
+                    assert(i > 0);
+                    if ((rule_arg[i - 1] & RULE_ARG_KIND_MASK) == RULE_ARG_OPT_RULE) {
+                        // an optional rule that failed, so continue with next arg
+                        push_result_node(&parser, MP_PARSE_NODE_NULL);
+                        backtrack = false;
+                    } else {
+                        // a mandatory rule that failed, so propagate backtrack
+                        if (i > 1) {
+                            // already eaten tokens so can't backtrack
+                            goto syntax_error;
+                        } else {
+                            goto next_rule;
+                        }
+                    }
+                }
+
+                // progress through the rule
+                for (; i < n; ++i) {
+                    if ((rule_arg[i] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
+                        // need to match a token
+                        mp_token_kind_t tok_kind = rule_arg[i] & RULE_ARG_ARG_MASK;
+                        if (lex->tok_kind == tok_kind) {
+                            // matched token
+                            if (tok_kind == MP_TOKEN_NAME) {
+                                push_result_token(&parser, rule_id);
+                            }
+                            mp_lexer_to_next(lex);
+                        } else {
+                            // failed to match token
+                            if (i > 0) {
+                                // already eaten tokens so can't backtrack
+                                goto syntax_error;
+                            } else {
+                                // this rule failed, so backtrack
+                                backtrack = true;
+                                goto next_rule;
+                            }
+                        }
+                    } else {
+                        push_rule(&parser, rule_src_line, rule_id, i + 1); // save this and-rule
+                        push_rule_from_arg(&parser, rule_arg[i]); // push child of and-rule
+                        goto next_rule;
+                    }
+                }
+
+                assert(i == n);
+
+                // matched the rule, so now build the corresponding parse_node
+
+                #if !MICROPY_ENABLE_DOC_STRING
+                // this code discards lonely statements, such as doc strings
+                if (input_kind != MP_PARSE_SINGLE_INPUT && rule_id == RULE_expr_stmt && peek_result(&parser, 0) == MP_PARSE_NODE_NULL) {
+                    mp_parse_node_t p = peek_result(&parser, 1);
+                    if ((MP_PARSE_NODE_IS_LEAF(p) && !MP_PARSE_NODE_IS_ID(p))
+                        || MP_PARSE_NODE_IS_STRUCT_KIND(p, RULE_const_object)) {
+                        pop_result(&parser); // MP_PARSE_NODE_NULL
+                        pop_result(&parser); // const expression (leaf or RULE_const_object)
+                        // Pushing the "pass" rule here will overwrite any RULE_const_object
+                        // entry that was on the result stack, allowing the GC to reclaim
+                        // the memory from the const object when needed.
+                        push_result_rule(&parser, rule_src_line, RULE_pass_stmt, 0);
+                        break;
+                    }
+                }
+                #endif
+
+                // count number of arguments for the parse node
+                i = 0;
+                size_t num_not_nil = 0;
+                for (size_t x = n; x > 0;) {
+                    --x;
+                    if ((rule_arg[x] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
+                        mp_token_kind_t tok_kind = rule_arg[x] & RULE_ARG_ARG_MASK;
+                        if (tok_kind == MP_TOKEN_NAME) {
+                            // only tokens which were names are pushed to stack
+                            i += 1;
+                            num_not_nil += 1;
+                        }
+                    } else {
+                        // rules are always pushed
+                        if (peek_result(&parser, i) != MP_PARSE_NODE_NULL) {
+                            num_not_nil += 1;
+                        }
+                        i += 1;
+                    }
+                }
+
+                if (num_not_nil == 1 && (rule_act & RULE_ACT_ALLOW_IDENT)) {
+                    // this rule has only 1 argument and should not be emitted
+                    mp_parse_node_t pn = MP_PARSE_NODE_NULL;
+                    for (size_t x = 0; x < i; ++x) {
+                        mp_parse_node_t pn2 = pop_result(&parser);
+                        if (pn2 != MP_PARSE_NODE_NULL) {
+                            pn = pn2;
+                        }
+                    }
+                    push_result_node(&parser, pn);
+                } else {
+                    // this rule must be emitted
+
+                    if (rule_act & RULE_ACT_ADD_BLANK) {
+                        // and add an extra blank node at the end (used by the compiler to store data)
+                        push_result_node(&parser, MP_PARSE_NODE_NULL);
+                        i += 1;
+                    }
+
+                    push_result_rule(&parser, rule_src_line, rule_id, i);
+                }
+                break;
+            }
+
+            default: {
+                assert((rule_act & RULE_ACT_KIND_MASK) == RULE_ACT_LIST);
+
+                // n=2 is: item item*
+                // n=1 is: item (sep item)*
+                // n=3 is: item (sep item)* [sep]
+                bool had_trailing_sep;
+                if (backtrack) {
+                list_backtrack:
+                    had_trailing_sep = false;
+                    if (n == 2) {
+                        if (i == 1) {
+                            // fail on item, first time round; propagate backtrack
+                            goto next_rule;
+                        } else {
+                            // fail on item, in later rounds; finish with this rule
+                            backtrack = false;
+                        }
+                    } else {
+                        if (i == 1) {
+                            // fail on item, first time round; propagate backtrack
+                            goto next_rule;
+                        } else if ((i & 1) == 1) {
+                            // fail on item, in later rounds; have eaten tokens so can't backtrack
+                            if (n == 3) {
+                                // list allows trailing separator; finish parsing list
+                                had_trailing_sep = true;
+                                backtrack = false;
+                            } else {
+                                // list doesn't allowing trailing separator; fail
+                                goto syntax_error;
+                            }
+                        } else {
+                            // fail on separator; finish parsing list
+                            backtrack = false;
+                        }
+                    }
+                } else {
+                    for (;;) {
+                        size_t arg = rule_arg[i & 1 & n];
+                        if ((arg & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
+                            if (lex->tok_kind == (arg & RULE_ARG_ARG_MASK)) {
+                                if (i & 1 & n) {
+                                    // separators which are tokens are not pushed to result stack
+                                } else {
+                                    push_result_token(&parser, rule_id);
+                                }
+                                mp_lexer_to_next(lex);
+                                // got element of list, so continue parsing list
+                                i += 1;
+                            } else {
+                                // couldn't get element of list
+                                i += 1;
+                                backtrack = true;
+                                goto list_backtrack;
+                            }
+                        } else {
+                            assert((arg & RULE_ARG_KIND_MASK) == RULE_ARG_RULE);
+                            push_rule(&parser, rule_src_line, rule_id, i + 1); // save this list-rule
+                            push_rule_from_arg(&parser, arg); // push child of list-rule
+                            goto next_rule;
+                        }
+                    }
+                }
+                assert(i >= 1);
+
+                // compute number of elements in list, result in i
+                i -= 1;
+                if ((n & 1) && (rule_arg[1] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
+                    // don't count separators when they are tokens
+                    i = (i + 1) / 2;
+                }
+
+                if (i == 1) {
+                    // list matched single item
+                    if (had_trailing_sep) {
+                        // if there was a trailing separator, make a list of a single item
+                        push_result_rule(&parser, rule_src_line, rule_id, i);
+                    } else {
+                        // just leave single item on stack (ie don't wrap in a list)
+                    }
+                } else {
+                    push_result_rule(&parser, rule_src_line, rule_id, i);
+                }
+                break;
+            }
+        }
+    }
+
+    #if MICROPY_COMP_CONST
+    mp_map_deinit(&parser.consts);
+    #endif
+
+    // truncate final chunk and link into chain of chunks
+    if (parser.cur_chunk != NULL) {
+        (void)m_renew_maybe(byte, parser.cur_chunk,
+            sizeof(mp_parse_chunk_t) + parser.cur_chunk->alloc,
+            sizeof(mp_parse_chunk_t) + parser.cur_chunk->union_.used,
+            false);
+        parser.cur_chunk->alloc = parser.cur_chunk->union_.used;
+        parser.cur_chunk->union_.next = parser.tree.chunk;
+        parser.tree.chunk = parser.cur_chunk;
+    }
+
+    if (
+        lex->tok_kind != MP_TOKEN_END // check we are at the end of the token stream
+        || parser.result_stack_top == 0 // check that we got a node (can fail on empty input)
+        ) {
+    syntax_error:;
+        mp_obj_t exc;
+        if (lex->tok_kind == MP_TOKEN_INDENT) {
+            exc = mp_obj_new_exception_msg(&mp_type_IndentationError,
+                MP_ERROR_TEXT("unexpected indent"));
+        } else if (lex->tok_kind == MP_TOKEN_DEDENT_MISMATCH) {
+            exc = mp_obj_new_exception_msg(&mp_type_IndentationError,
+                MP_ERROR_TEXT("unindent doesn't match any outer indent level"));
+        #if MICROPY_PY_FSTRINGS
+        } else if (lex->tok_kind == MP_TOKEN_MALFORMED_FSTRING) {
+            exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
+                MP_ERROR_TEXT("malformed f-string"));
+        } else if (lex->tok_kind == MP_TOKEN_FSTRING_RAW) {
+            exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
+                MP_ERROR_TEXT("raw f-strings are not supported"));
+        #endif
+        } else {
+            exc = mp_obj_new_exception_msg(&mp_type_SyntaxError,
+                MP_ERROR_TEXT("invalid syntax"));
+        }
+        // add traceback to give info about file name and location
+        // we don't have a 'block' name, so just pass the NULL qstr to indicate this
+        mp_obj_exception_add_traceback(exc, lex->source_name, lex->tok_line, MP_QSTRnull);
+        nlr_raise(exc);
+    }
+
+    // get the root parse node that we created
+    assert(parser.result_stack_top == 1);
+    parser.tree.root = parser.result_stack[0];
+
+    // free the memory that we don't need anymore
+    m_del(rule_stack_t, parser.rule_stack, parser.rule_stack_alloc);
+    m_del(mp_parse_node_t, parser.result_stack, parser.result_stack_alloc);
+
+    // we also free the lexer on behalf of the caller
+    mp_lexer_free(lex);
+
+    return parser.tree;
+}
+
+void mp_parse_tree_clear(mp_parse_tree_t *tree) {
+    mp_parse_chunk_t *chunk = tree->chunk;
+    while (chunk != NULL) {
+        mp_parse_chunk_t *next = chunk->union_.next;
+        m_del(byte, chunk, sizeof(mp_parse_chunk_t) + chunk->alloc);
+        chunk = next;
+    }
+}
+
+#endif // MICROPY_ENABLE_COMPILER