source: mainline/uspace/app/bithenge/script.c@ d8bd2ec

/*
 * Copyright (c) 2012 Sean Bartell
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup bithenge
 * @{
 */
/**
 * @file
 * Script parsing.
 */

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include "expression.h"
#include "os.h"
#include "script.h"
#include "sequence.h"
#include "transform.h"
#include "tree.h"

/** Tokens with more characters than this may be read incorrectly. */
#define MAX_TOKEN_SIZE 256
#define BUFFER_SIZE 4096

/** Single-character symbols are represented by the character itself. Every
 * other token uses one of these values: */
typedef enum {
        TOKEN_EQUALS = -128,
        TOKEN_ERROR,
        TOKEN_EOF,
        TOKEN_IDENTIFIER,
        TOKEN_INTEGER,
        TOKEN_LEFT_ARROW,

        /* Keywords */
        TOKEN_DO,
        TOKEN_ELSE,
        TOKEN_FALSE,
        TOKEN_IF,
        TOKEN_IN,
        TOKEN_REPEAT,
        TOKEN_STRUCT,
        TOKEN_SWITCH,
        TOKEN_TRANSFORM,
        TOKEN_TRUE,
        TOKEN_WHILE,
} token_type_t;

/** Singly-linked list of named transforms. */
typedef struct transform_list {
        char *name;
        bithenge_transform_t *transform;
        struct transform_list *next;
} transform_list_t;

/** State kept by the parser. */
typedef struct {
        /** Rather than constantly checking return values, the parser uses this
         * to indicate whether an error has occurred. */
        int error;

        /** The list of named transforms. */
        transform_list_t *transform_list;

        /** The name of the script file. */
        const char *filename;
        /** The script file being read from. */
        FILE *file;
        /** The buffer that holds script code. There is always a '\0' after the
         * current position to prevent reading too far. */
        char buffer[BUFFER_SIZE];
        /** The start position within the buffer of the next unread token. */
        size_t buffer_pos;
        /** The start position within the buffer of the current token. */
        size_t old_buffer_pos;
        /** The line number of the current token. */
        int lineno;
        /** Added to a buffer position to find the column number. */
        int line_offset;

        /** The type of the current token. */
        token_type_t token;
        union {
                /** The value of a TOKEN_IDENTIFIER token. Unless changed to
                 * NULL, it will be freed when the next token is read. */
                char *token_string;
                /** The value of a TOKEN_INTEGER token. */
                bithenge_int_t token_int;
        };

        /** The names of the current transform's parameters. */
        char **parameter_names;
        /** The number of parameters. */
        int num_params;
        /** @a parse_expression sets this when TOKEN_IN is used. */
        bool in_node_used;
} state_t;

/** Free the previous token's data. This must be called before changing
 * state->token. */
static void done_with_token(state_t *state)
{
        if (state->token == TOKEN_IDENTIFIER)
                free(state->token_string);
        state->token = TOKEN_ERROR;
}

/** Note that an error has occurred if error is not EOK. */
static void error_errno(state_t *state, int error)
{
        // Don't overwrite a previous error.
        if (state->error == EOK && error != EOK) {
                done_with_token(state);
                state->token = TOKEN_ERROR;
                state->error = error;
        }
}

/** Note that a syntax error has occurred and print an error message. */
static void syntax_error(state_t *state, const char *message)
{
        // Printing multiple errors is confusing.
        if (state->error == EOK) {
                size_t start_char = state->old_buffer_pos + state->line_offset;
                size_t end_char = state->buffer_pos + state->line_offset;
                size_t size = end_char - start_char;
                fprintf(stderr, "%s:%d:", state->filename, state->lineno);
                if (size <= 1)
                        fprintf(stderr, "%zd: ", start_char);
                else
                        fprintf(stderr, "%zd-%zd: ", start_char, end_char - 1);
                fprintf(stderr, "%s: \"%.*s\"\n", message, (int)size,
                    state->buffer + state->old_buffer_pos);
                error_errno(state, EINVAL);
        }
}

/** Ensure the buffer contains enough characters to read a token. */
static void fill_buffer(state_t *state)
{
        if (state->buffer_pos + MAX_TOKEN_SIZE < BUFFER_SIZE)
                return;

        size_t empty_size = state->buffer_pos;
        size_t used_size = BUFFER_SIZE - 1 - state->buffer_pos;
        memmove(state->buffer, state->buffer + state->buffer_pos, used_size);
        state->line_offset += state->buffer_pos;
        state->buffer_pos = 0;

        size_t read_size = fread(state->buffer + used_size, 1, empty_size,
            state->file);
        if (ferror(state->file))
                error_errno(state, EIO);
        state->buffer[used_size + read_size] = '\0';
}

/** Read the next token. */
static void next_token(state_t *state)
{
        fill_buffer(state);
        done_with_token(state);
        state->old_buffer_pos = state->buffer_pos;
        char ch = state->buffer[state->buffer_pos];
        if (ch == '\0') {
                state->token = TOKEN_EOF;
        } else if (ch == '#') {
                while (state->buffer[state->buffer_pos] != '\n'
                    && state->buffer[state->buffer_pos] != '\0') {
                        state->buffer_pos++;
                        fill_buffer(state);
                }
                next_token(state);
                return;
        } else if (isspace(ch)) {
                // Will eventually reach the '\0' at the end
                while (isspace(state->buffer[state->buffer_pos])) {
                        if (state->buffer[state->buffer_pos] == '\n') {
                                state->lineno++;
                                state->line_offset = -state->buffer_pos;
                        }
                        state->buffer_pos++;
                }
                next_token(state);
                return;
        } else if (isalpha(ch)) {
                while (isalnum(state->buffer[state->buffer_pos])
                    || state->buffer[state->buffer_pos] == '_')
                        state->buffer_pos++;
                char *value = str_ndup(state->buffer + state->old_buffer_pos,
                    state->buffer_pos - state->old_buffer_pos);
                if (!value) {
                        error_errno(state, ENOMEM);
                } else if (!str_cmp(value, "do")) {
                        state->token = TOKEN_DO;
                        free(value);
                } else if (!str_cmp(value, "else")) {
                        state->token = TOKEN_ELSE;
                        free(value);
                } else if (!str_cmp(value, "false")) {
                        state->token = TOKEN_FALSE;
                        free(value);
                } else if (!str_cmp(value, "if")) {
                        state->token = TOKEN_IF;
                        free(value);
                } else if (!str_cmp(value, "in")) {
                        state->token = TOKEN_IN;
                        free(value);
                } else if (!str_cmp(value, "repeat")) {
                        state->token = TOKEN_REPEAT;
                        free(value);
                } else if (!str_cmp(value, "struct")) {
                        state->token = TOKEN_STRUCT;
                        free(value);
                } else if (!str_cmp(value, "switch")) {
                        state->token = TOKEN_SWITCH;
                        free(value);
                } else if (!str_cmp(value, "transform")) {
                        state->token = TOKEN_TRANSFORM;
                        free(value);
                } else if (!str_cmp(value, "true")) {
                        state->token = TOKEN_TRUE;
                        free(value);
                } else if (!str_cmp(value, "while")) {
                        state->token = TOKEN_WHILE;
                        free(value);
                } else {
                        state->token = TOKEN_IDENTIFIER;
                        state->token_string = value;
                }
        } else if (isdigit(ch)) {
                while (isdigit(state->buffer[state->buffer_pos]))
                        state->buffer_pos++;
                state->token = TOKEN_INTEGER;
                int rc = bithenge_parse_int(state->buffer +
                    state->old_buffer_pos, &state->token_int);
                error_errno(state, rc);
        } else if (ch == '<') {
                state->token = ch;
                state->buffer_pos++;
                if (state->buffer[state->buffer_pos] == '-') {
                        state->buffer_pos++;
                        state->token = TOKEN_LEFT_ARROW;
                }
        } else if (ch == '=') {
                state->token = ch;
                state->buffer_pos++;
                if (state->buffer[state->buffer_pos] == '=') {
                        state->token = TOKEN_EQUALS;
                        state->buffer_pos++;
                }
        } else {
                state->token = ch;
                state->buffer_pos++;
        }
}

/** Allocate memory and handle failure by setting the error in the state. The
 * caller must check the state for errors before using the return value of this
 * function. */
static void *state_malloc(state_t *state, size_t size)
{
        if (state->error != EOK)
                return NULL;
        void *result = malloc(size);
        if (result == NULL)
                error_errno(state, ENOMEM);
        return result;
}

/** Reallocate memory and handle failure by setting the error in the state. If
 * an error occurs, the existing pointer will be returned. */
static void *state_realloc(state_t *state, void *ptr, size_t size)
{
        if (state->error != EOK)
                return ptr;
        void *result = realloc(ptr, size);
        if (result == NULL) {
                error_errno(state, ENOMEM);
                return ptr;
        }
        return result;
}

/** Expect and consume a certain token. If the next token is of the wrong type,
 * an error is caused. */
static void expect(state_t *state, token_type_t type)
{
        if (state->token != type) {
                syntax_error(state, "unexpected");
                return;
        }
        next_token(state);
}

/** Expect and consume an identifier token. If the next token is not an
 * identifier, an error is caused and this function returns null. */
static char *expect_identifier(state_t *state)
{
        if (state->token != TOKEN_IDENTIFIER) {
                syntax_error(state, "unexpected (identifier expected)");
                return NULL;
        }
        char *val = state->token_string;
        state->token_string = NULL;
        next_token(state);
        return val;
}

/** Find a transform by name. A reference will be added to the transform.
 * @return The found transform, or NULL if none was found. */
static bithenge_transform_t *get_named_transform(state_t *state,
    const char *name)
{
        for (transform_list_t *e = state->transform_list; e; e = e->next) {
                if (!str_cmp(e->name, name)) {
                        bithenge_transform_inc_ref(e->transform);
                        return e->transform;
                }
        }
        for (int i = 0; bithenge_primitive_transforms[i].name; i++) {
                if (!str_cmp(bithenge_primitive_transforms[i].name, name)) {
                        bithenge_transform_t *xform =
                            bithenge_primitive_transforms[i].transform;
                        bithenge_transform_inc_ref(xform);
                        return xform;
                }
        }
        return NULL;
}

/** Add a named transform. This function takes ownership of the name and a
 * reference to the transform. If an error has occurred, either may be null. */
static void add_named_transform(state_t *state, bithenge_transform_t *xform, char *name)
{
        transform_list_t *entry = state_malloc(state, sizeof(*entry));
        if (state->error != EOK) {
                free(name);
                bithenge_transform_dec_ref(xform);
                free(entry);
                return;
        }
        entry->name = name;
        entry->transform = xform;
        entry->next = state->transform_list;
        state->transform_list = entry;
}

static bithenge_transform_t *parse_transform(state_t *state);
static bithenge_transform_t *parse_struct(state_t *state);
static bithenge_expression_t *parse_expression(state_t *state);



/***************** Expressions                               *****************/

typedef enum {
        PRECEDENCE_NONE,
        PRECEDENCE_EQUALS,
        PRECEDENCE_ADD,
        PRECEDENCE_MULTIPLY,
} precedence_t;

static bithenge_binary_op_t token_as_binary_operator(token_type_t token)
{
        switch ((int)token) {
        case '+':
                return BITHENGE_EXPRESSION_ADD;
        case '-':
                return BITHENGE_EXPRESSION_SUBTRACT;
        case '*':
                return BITHENGE_EXPRESSION_MULTIPLY;
        case TOKEN_EQUALS:
                return BITHENGE_EXPRESSION_EQUALS;
        default:
                return BITHENGE_EXPRESSION_INVALID_BINARY_OP;
        }
}

static precedence_t binary_operator_precedence(bithenge_binary_op_t op)
{
        switch (op) {
        case BITHENGE_EXPRESSION_ADD: /* fallthrough */
        case BITHENGE_EXPRESSION_SUBTRACT:
                return PRECEDENCE_ADD;
        case BITHENGE_EXPRESSION_MULTIPLY:
                return PRECEDENCE_MULTIPLY;
        case BITHENGE_EXPRESSION_EQUALS:
                return PRECEDENCE_EQUALS;
        default:
                assert(false);
                return PRECEDENCE_NONE;
        }
}

static bithenge_expression_t *parse_term(state_t *state)
{
        int rc;
        if (state->token == TOKEN_TRUE || state->token == TOKEN_FALSE) {
                bool val = state->token == TOKEN_TRUE;
                next_token(state);
                bithenge_node_t *node;
                rc = bithenge_new_boolean_node(&node, val);
                if (rc != EOK) {
                        error_errno(state, rc);
                        return NULL;
                }

                bithenge_expression_t *expr;
                rc = bithenge_const_expression(&expr, node);
                if (rc != EOK) {
                        error_errno(state, rc);
                        return NULL;
                }

                return expr;
        } else if (state->token == TOKEN_IN) {
                next_token(state);
                state->in_node_used = true;
                bithenge_expression_t *expr;
                rc = bithenge_in_node_expression(&expr);
                if (rc != EOK) {
                        error_errno(state, rc);
                        return NULL;
                }
                return expr;
        } else if (state->token == TOKEN_INTEGER) {
                bithenge_int_t val = state->token_int;
                next_token(state);
                bithenge_node_t *node;
                rc = bithenge_new_integer_node(&node, val);
                if (rc != EOK) {
                        error_errno(state, rc);
                        return NULL;
                }

                bithenge_expression_t *expr;
                rc = bithenge_const_expression(&expr, node);
                if (rc != EOK) {
                        error_errno(state, rc);
                        return NULL;
                }

                return expr;
        } else if (state->token == TOKEN_IDENTIFIER) {
                int i;
                for (i = 0; i < state->num_params; i++)
                        if (!str_cmp(state->parameter_names[i],
                            state->token_string))
                                break;

                if (i == state->num_params) {
                        syntax_error(state, "unknown identifier");
                        return NULL;
                }

                bithenge_expression_t *expr;
                rc = bithenge_param_expression(&expr, i);
                if (rc != EOK) {
                        error_errno(state, rc);
                        return NULL;
                }

                next_token(state);

                return expr;
        } else if (state->token == '.') {
                next_token(state);

                const char *id = expect_identifier(state);
                bithenge_node_t *key = NULL;
                bithenge_expression_t *expr = NULL;

                if (state->error == EOK) {
                        rc = bithenge_new_string_node(&key, id, true);
                        id = NULL;
                        error_errno(state, rc);
                }

                if (state->error == EOK) {
                        rc = bithenge_scope_member_expression(&expr, key);
                        key = NULL;
                        if (rc != EOK)
                                expr = NULL;
                        error_errno(state, rc);
                }

                if (state->error != EOK) {
                        free((char *)id);
                        bithenge_node_dec_ref(key);
                        bithenge_expression_dec_ref(expr);
                        return NULL;
                }

                return expr;
        } else if (state->token == '(') {
                next_token(state);
                bithenge_expression_t *expr = parse_expression(state);
                expect(state, ')');
                return expr;
        } else {
                syntax_error(state, "expression expected");
                return NULL;
        }
}

static bithenge_expression_t *parse_expression_precedence(state_t *state,
    precedence_t prev_precedence)
{
        bithenge_expression_t *expr = parse_term(state);
        while (state->error == EOK) {
                bithenge_binary_op_t op =
                    token_as_binary_operator(state->token);
                if (op == BITHENGE_EXPRESSION_INVALID_BINARY_OP)
                        break;
                precedence_t precedence = binary_operator_precedence(op);
                if (precedence <= prev_precedence)
                        break;
                next_token(state);

                bithenge_expression_t *expr2 = parse_term(state);
                if (state->error != EOK) {
                        bithenge_expression_dec_ref(expr2);
                        break;
                }
                int rc = bithenge_binary_expression(&expr, op, expr, expr2);
                if (rc != EOK)
                        error_errno(state, rc);
        }
        if (state->error != EOK) {
                bithenge_expression_dec_ref(expr);
                expr = NULL;
        }
        return expr;
}

static bithenge_expression_t *parse_expression(state_t *state)
{
        return parse_expression_precedence(state, PRECEDENCE_NONE);
}



/* state->token must be TOKEN_IDENTIFIER when this is called. */
static bithenge_transform_t *parse_invocation(state_t *state)
{
        bithenge_transform_t *result = get_named_transform(state,
            state->token_string);
        if (!result)
                syntax_error(state, "transform not found");
        next_token(state);

        bithenge_expression_t **params = NULL;
        int num_params = 0;
        if (state->token == '(') {
                next_token(state);
                while (state->error == EOK && state->token != ')') {
                        if (num_params)
                                expect(state, ',');
                        params = state_realloc(state, params,
                            (num_params + 1)*sizeof(*params));
                        if (state->error != EOK)
                                break;
                        params[num_params] = parse_expression(state);
                        num_params++;
                }
                expect(state, ')');
        }

        /* TODO: show correct error position */
        if (state->error == EOK
            && bithenge_transform_num_params(result) != num_params)
                syntax_error(state, "incorrect number of parameters before");

        if (state->error != EOK) {
                while (num_params--)
                        bithenge_expression_dec_ref(params[num_params]);
                free(params);
                bithenge_transform_dec_ref(result);
                return NULL;
        }

        if (num_params) {
                int rc = bithenge_param_wrapper(&result, result, params);
                if (rc != EOK) {
                        error_errno(state, rc);
                        result = NULL;
                }
        }

        return result;
}

/** Create a transform that just produces an empty node.
 * @param state The parser state.
 * @return The new transform, or NULL on error. */
static bithenge_transform_t *make_empty_transform(state_t *state)
{
        bithenge_node_t *node;
        int rc = bithenge_new_empty_internal_node(&node);
        if (rc != EOK) {
                error_errno(state, rc);
                return NULL;
        }

        bithenge_expression_t *expr;
        rc = bithenge_const_expression(&expr, node);
        if (rc != EOK) {
                error_errno(state, rc);
                return NULL;
        }

        bithenge_transform_t *xform;
        rc = bithenge_inputless_transform(&xform, expr);
        if (rc != EOK) {
                error_errno(state, rc);
                return NULL;
        }

        return xform;
}

static bithenge_transform_t *parse_if(state_t *state, bool in_struct)
{
        expect(state, TOKEN_IF);
        expect(state, '(');
        bithenge_expression_t *expr = parse_expression(state);
        expect(state, ')');
        expect(state, '{');
        bithenge_transform_t *true_xform =
            in_struct ? parse_struct(state) : parse_transform(state);
        expect(state, '}');

        bithenge_transform_t *false_xform = NULL;
        if (state->token == TOKEN_ELSE) {
                next_token(state);
                expect(state, '{');
                false_xform =
                    in_struct ? parse_struct(state) : parse_transform(state);
                expect(state, '}');
        } else {
                if (in_struct)
                        false_xform = make_empty_transform(state);
                else
                        syntax_error(state, "else expected");
        }

        if (state->error != EOK) {
                bithenge_expression_dec_ref(expr);
                bithenge_transform_dec_ref(true_xform);
                bithenge_transform_dec_ref(false_xform);
                return NULL;
        }

        bithenge_transform_t *if_xform;
        int rc = bithenge_if_transform(&if_xform, expr, true_xform,
            false_xform);
        if (rc != EOK) {
                error_errno(state, rc);
                return NULL;
        }
        return if_xform;
}

static bithenge_transform_t *parse_switch(state_t *state, bool in_struct)
{
        expect(state, TOKEN_SWITCH);
        expect(state, '(');
        bithenge_expression_t *ref_expr = parse_expression(state);
        expect(state, ')');
        expect(state, '{');
        int num = 0;
        bithenge_expression_t **exprs = NULL;
        bithenge_transform_t **xforms = NULL;
        while (state->error == EOK && state->token != '}') {
                bithenge_expression_t *expr;
                if (state->token == TOKEN_ELSE) {
                        next_token(state);
                        bithenge_node_t *node;
                        int rc = bithenge_new_boolean_node(&node, true);
                        if (rc != EOK) {
                                error_errno(state, rc);
                                break;
                        }
                        rc = bithenge_const_expression(&expr, node);
                        if (rc != EOK) {
                                error_errno(state, rc);
                                break;
                        }
                } else {
                        expr = parse_expression(state);
                        if (state->error == EOK) {
                                bithenge_expression_inc_ref(ref_expr);
                                int rc = bithenge_binary_expression(&expr,
                                    BITHENGE_EXPRESSION_EQUALS, ref_expr,
                                    expr);
                                if (rc != EOK) {
                                        error_errno(state, rc);
                                        break;
                                }
                        }
                }

                expect(state, ':');
                bithenge_transform_t *xform;
                if (in_struct) {
                        expect(state, '{');
                        xform = parse_struct(state);
                        expect(state, '}');
                } else
                        xform = parse_transform(state);
                expect(state, ';');

                exprs = state_realloc(state, exprs,
                    sizeof(*exprs) * (num + 1));
                xforms = state_realloc(state, xforms,
                    sizeof(*xforms) * (num + 1));
                if (state->error != EOK) {
                        bithenge_expression_dec_ref(expr);
                        bithenge_transform_dec_ref(xform);
                        break;
                }

                exprs[num] = expr;
                xforms[num] = xform;
                num++;
        }
        bithenge_expression_dec_ref(ref_expr);

        bithenge_transform_t *switch_xform = &bithenge_invalid_transform;
        bithenge_transform_inc_ref(switch_xform);
        while (state->error == EOK && num >= 1) {
                num--;
                int rc = bithenge_if_transform(&switch_xform, exprs[num],
                    xforms[num], switch_xform);
                if (rc != EOK)
                        error_errno(state, rc);
        }

        while (num >= 1) {
                num--;
                bithenge_expression_dec_ref(exprs[num]);
                bithenge_transform_dec_ref(xforms[num]);
        }
        free(exprs);
        free(xforms);

        expect(state, '}');
        return switch_xform;
}

static bithenge_transform_t *parse_repeat(state_t *state)
{
        expect(state, TOKEN_REPEAT);
        bithenge_expression_t *expr = NULL;
        if (state->token == '(') {
                next_token(state);
                expr = parse_expression(state);
                expect(state, ')');
        }
        expect(state, '{');
        bithenge_transform_t *xform = parse_transform(state);
        expect(state, '}');

        if (state->error != EOK) {
                bithenge_expression_dec_ref(expr);
                bithenge_transform_dec_ref(xform);
                return NULL;
        }

        bithenge_transform_t *repeat_xform;
        int rc = bithenge_repeat_transform(&repeat_xform, xform, expr);
        if (rc != EOK) {
                error_errno(state, rc);
                return NULL;
        }
        return repeat_xform;
}

static bithenge_transform_t *parse_do_while(state_t *state)
{
        expect(state, TOKEN_DO);
        expect(state, '{');
        bithenge_transform_t *xform = parse_transform(state);
        expect(state, '}');
        expect(state, TOKEN_WHILE);
        expect(state, '(');
        bithenge_expression_t *expr = parse_expression(state);
        expect(state, ')');

        if (state->error != EOK) {
                bithenge_expression_dec_ref(expr);
                bithenge_transform_dec_ref(xform);
                return NULL;
        }

        bithenge_transform_t *do_while_xform;
        int rc = bithenge_do_while_transform(&do_while_xform, xform, expr);
        if (rc != EOK) {
                error_errno(state, rc);
                return NULL;
        }
        return do_while_xform;
}

/* The TOKEN_STRUCT and '{' must already have been skipped. */
static bithenge_transform_t *parse_struct(state_t *state)
{
        size_t num = 0;
        bithenge_named_transform_t *subxforms;
        /* We keep an extra space for the {NULL, NULL} terminator. */
        subxforms = state_malloc(state, sizeof(*subxforms));
        while (state->error == EOK && state->token != '}') {
                if (state->token == TOKEN_IF) {
                        subxforms[num].transform = parse_if(state, true);
                        subxforms[num].name = NULL;
                } else if (state->token == TOKEN_SWITCH) {
                        subxforms[num].transform = parse_switch(state, true);
                        subxforms[num].name = NULL;
                } else {
                        if (state->token == '.') {
                                next_token(state);
                                subxforms[num].name = expect_identifier(state);
                        } else {
                                subxforms[num].name = NULL;
                        }
                        expect(state, TOKEN_LEFT_ARROW);
                        subxforms[num].transform = parse_transform(state);
                        expect(state, ';');
                }
                num++;
                subxforms = state_realloc(state, subxforms,
                    (num + 1)*sizeof(*subxforms));
        }

        if (state->error != EOK) {
                while (num--) {
                        free((void *)subxforms[num].name);
                        bithenge_transform_dec_ref(subxforms[num].transform);
                }
                free(subxforms);
                return NULL;
        }

        subxforms[num].name = NULL;
        subxforms[num].transform = NULL;
        bithenge_transform_t *result;
        int rc = bithenge_new_struct(&result, subxforms);
        if (rc != EOK) {
                error_errno(state, rc);
                return NULL;
        }
        return result;
}

/** Parse a transform without composition.
 * @return The parsed transform, or NULL if an error occurred. */
static bithenge_transform_t *parse_transform_no_compose(state_t *state)
{
        if (state->token == '(') {
                next_token(state);
                state->in_node_used = false;
                bithenge_expression_t *expr = parse_expression(state);
                expect(state, ')');
                if (state->error != EOK) {
                        bithenge_expression_dec_ref(expr);
                        return NULL;
                }

                bithenge_transform_t *xform;
                int rc;
                if (state->in_node_used)
                        rc = bithenge_expression_transform(&xform, expr);
                else
                        rc = bithenge_inputless_transform(&xform, expr);
                if (rc != EOK) {
                        error_errno(state, rc);
                        return NULL;
                }
                return xform;
        } else if (state->token == TOKEN_DO) {
                return parse_do_while(state);
        } else if (state->token == TOKEN_IDENTIFIER) {
                return parse_invocation(state);
        } else if (state->token == TOKEN_IF) {
                return parse_if(state, false);
        } else if (state->token == TOKEN_REPEAT) {
                return parse_repeat(state);
        } else if (state->token == TOKEN_STRUCT) {
                next_token(state);
                expect(state, '{');
                bithenge_transform_t *xform = parse_struct(state);
                expect(state, '}');
                return xform;
        } else if (state->token == TOKEN_SWITCH) {
                return parse_switch(state, false);
        } else {
                syntax_error(state, "unexpected (transform expected)");
                return NULL;
        }
}

/** Parse a transform.
 * @return The parsed transform, or NULL if an error occurred. */
static bithenge_transform_t *parse_transform(state_t *state)
{
        bithenge_transform_t *result = parse_transform_no_compose(state);
        bithenge_transform_t **xforms = NULL;
        size_t num = 1;
        while (state->token == TOKEN_LEFT_ARROW) {
                expect(state, TOKEN_LEFT_ARROW);
                xforms = state_realloc(state, xforms,
                    (num + 1) * sizeof(*xforms));
                if (state->error != EOK)
                        break;
                xforms[num] = parse_transform_no_compose(state);
                num++;
        }
        if (state->error != EOK) {
                while (xforms && num--)
                        bithenge_transform_dec_ref(xforms[num]);
                free(xforms);
                bithenge_transform_dec_ref(result);
                return NULL;
        }
        if (xforms) {
                xforms[0] = result;
                int rc = bithenge_new_composed_transform(&result, xforms, num);
                if (rc != EOK) {
                        error_errno(state, rc);
                        return NULL;
                }
        }
        return result;
}

/** Parse a definition. */
static void parse_definition(state_t *state)
{
        expect(state, TOKEN_TRANSFORM);
        char *name = expect_identifier(state);

        if (state->token == '(') {
                next_token(state);
                while (state->error == EOK && state->token != ')') {
                        if (state->num_params)
                                expect(state, ',');
                        state->parameter_names = state_realloc(state,
                            state->parameter_names,
                            (state->num_params + 1)*sizeof(*state->parameter_names));
                        if (state->error != EOK)
                                break;
                        state->parameter_names[state->num_params++] =
                            expect_identifier(state);
                }
                expect(state, ')');
        }

        expect(state, '=');
        bithenge_transform_t *xform = parse_transform(state);
        expect(state, ';');

        if (state->error == EOK) {
                int rc = bithenge_new_barrier_transform(&xform, xform,
                    state->num_params);
                if (rc != EOK) {
                        xform = NULL;
                        error_errno(state, rc);
                }
        }

        add_named_transform(state, xform, name);

        for (int i = 0; i < state->num_params; i++)
                free(state->parameter_names[i]);
        free(state->parameter_names);
        state->parameter_names = NULL;
        state->num_params = 0;
}

/** Initialize the state. */
static void state_init(state_t *state, const char *filename)
{
        state->error = EOK;
        state->transform_list = NULL;
        state->parameter_names = NULL;
        state->num_params = 0;
        state->token = TOKEN_ERROR;
        state->old_buffer_pos = state->buffer_pos = BUFFER_SIZE - 1;
        state->lineno = 1;
        state->line_offset = (int)-state->buffer_pos + 1;
        state->filename = filename;
        state->file = fopen(filename, "r");
        if (!state->file) {
                error_errno(state, errno);
        } else {
                next_token(state);
        }
}

/** Destroy the state. */
static void state_destroy(state_t *state)
{
        done_with_token(state);
        state->token = TOKEN_ERROR;
        if (state->file)
                fclose(state->file);
        transform_list_t *entry = state->transform_list;
        while (entry) {
                transform_list_t *next = entry->next;
                free(entry->name);
                bithenge_transform_dec_ref(entry->transform);
                free(entry);
                entry = next;
        }
        for (int i = 0; i < state->num_params; i++)
                free(state->parameter_names[i]);
        free(state->parameter_names);
}

/** Parse a script file.
 * @param filename The name of the script file.
 * @param[out] out Stores the "main" transform.
 * @return EOK on success, EINVAL on syntax error, or an error code from
 * errno.h. */
int bithenge_parse_script(const char *filename, bithenge_transform_t **out)
{
        state_t state;
        state_init(&state, filename);
        while (state.error == EOK && state.token != TOKEN_EOF)
                parse_definition(&state);
        *out = get_named_transform(&state, "main");
        int rc = state.error;
        state_destroy(&state);
        if (rc == EOK && !*out) {
                fprintf(stderr, "no \"main\" transform\n");
                rc = EINVAL;
        }
        return rc;
}

/** @}
 */