pub(crate) const KW_IMPORT:    &'static [u8] = b"import";

// Keywords - literals

pub(crate) const KW_LIT_TRUE:  &'static [u8] = b"true";

pub(crate) const KW_LIT_FALSE: &'static [u8] = b"false";

pub(crate) const KW_LIT_NULL:  &'static [u8] = b"null";

// Keywords - function(like)s

pub(crate) const KW_CAST:        &'static [u8] = b"cast";

pub(crate) const KW_FUNC_GET:    &'static [u8] = b"get";

pub(crate) const KW_FUNC_PUT:    &'static [u8] = b"put";

pub(crate) const KW_FUNC_FIRES:  &'static [u8] = b"fires";

pub(crate) const KW_FUNC_CREATE: &'static [u8] = b"create";

pub(crate) const KW_FUNC_LENGTH: &'static [u8] = b"length";

pub(crate) const KW_FUNC_ASSERT: &'static [u8] = b"assert";

// Keywords - statements

pub(crate) const KW_STMT_CHANNEL:  &'static [u8] = b"channel";

pub(crate) const KW_STMT_IF:       &'static [u8] = b"if";

pub(crate) const KW_STMT_ELSE:     &'static [u8] = b"else";

pub(crate) const KW_STMT_WHILE:    &'static [u8] = b"while";

pub(crate) const KW_STMT_BREAK:    &'static [u8] = b"break";

pub(crate) const KW_STMT_CONTINUE: &'static [u8] = b"continue";

pub(crate) const KW_STMT_GOTO:     &'static [u8] = b"goto";

pub(crate) const KW_STMT_RETURN:   &'static [u8] = b"return";

pub(crate) const KW_STMT_SYNC:     &'static [u8] = b"synchronous";

pub(crate) const KW_STMT_NEW:      &'static [u8] = b"new";

// Keywords - types

// Since types are needed for returning diagnostic information to the user, the

// string variants are put here as well.

pub(crate) const KW_TYPE_IN_PORT_STR:  &'static str = "in";

pub(crate) const KW_TYPE_OUT_PORT_STR: &'static str = "out";

pub(crate) const KW_TYPE_MESSAGE_STR:  &'static str = "msg";

pub(crate) const KW_TYPE_BOOL_STR:     &'static str = "bool";

pub(crate) const KW_TYPE_UINT8_STR:    &'static str = "u8";

pub(crate) const KW_TYPE_UINT16_STR:   &'static str = "u16";

pub(crate) const KW_TYPE_UINT32_STR:   &'static str = "u32";

pub(crate) const KW_TYPE_UINT64_STR:   &'static str = "u64";

pub(crate) const KW_TYPE_SINT8_STR:    &'static str = "s8";

pub(crate) const KW_TYPE_SINT16_STR:   &'static str = "s16";

pub(crate) const KW_TYPE_SINT32_STR:   &'static str = "s32";

pub(crate) const KW_TYPE_SINT64_STR:   &'static str = "s64";

pub(crate) const KW_TYPE_CHAR_STR:     &'static str = "char";

pub(crate) const KW_TYPE_STRING_STR:   &'static str = "string";

pub(crate) const KW_TYPE_INFERRED_STR: &'static str = "auto";

pub(crate) const KW_TYPE_IN_PORT:  &'static [u8] = KW_TYPE_IN_PORT_STR.as_bytes();

pub(crate) const KW_TYPE_OUT_PORT: &'static [u8] = KW_TYPE_OUT_PORT_STR.as_bytes();

pub(crate) const KW_TYPE_MESSAGE:  &'static [u8] = KW_TYPE_MESSAGE_STR.as_bytes();

pub(crate) const KW_TYPE_BOOL:     &'static [u8] = KW_TYPE_BOOL_STR.as_bytes();

pub(crate) const KW_TYPE_UINT8:    &'static [u8] = KW_TYPE_UINT8_STR.as_bytes();

pub(crate) const KW_TYPE_UINT16:   &'static [u8] = KW_TYPE_UINT16_STR.as_bytes();

pub(crate) const KW_TYPE_UINT32:   &'static [u8] = KW_TYPE_UINT32_STR.as_bytes();

pub(crate) const KW_TYPE_UINT64:   &'static [u8] = KW_TYPE_UINT64_STR.as_bytes();

pub(crate) const KW_TYPE_SINT8:    &'static [u8] = KW_TYPE_SINT8_STR.as_bytes();

pub(crate) const KW_TYPE_SINT16:   &'static [u8] = KW_TYPE_SINT16_STR.as_bytes();

pub(crate) const KW_TYPE_SINT32:   &'static [u8] = KW_TYPE_SINT32_STR.as_bytes();

pub(crate) const KW_TYPE_SINT64:   &'static [u8] = KW_TYPE_SINT64_STR.as_bytes();

pub(crate) const KW_TYPE_CHAR:     &'static [u8] = KW_TYPE_CHAR_STR.as_bytes();

pub(crate) const KW_TYPE_STRING:   &'static [u8] = KW_TYPE_STRING_STR.as_bytes();

pub(crate) const KW_TYPE_INFERRED: &'static [u8] = KW_TYPE_INFERRED_STR.as_bytes();

/// A special trait for when consuming comma-separated things such that we can

/// push them onto a `Vec` and onto a `ScopedSection`. As we monomorph for

/// very specific comma-separated cases I don't expect polymorph bloat.

/// Also, I really don't like this solution.

pub(crate) trait Extendable {

    type Value;

    fn push(&mut self, v: Self::Value);

}

impl<T> Extendable for Vec<T> {

    type Value = T;

    #[inline]

    fn push(&mut self, v: Self::Value) {

        (self as &mut Vec<T>).push(v);

    }

}

impl<T: Sized> Extendable for ScopedSection<T> {

    type Value = T;

    #[inline]

    fn push(&mut self, v: Self::Value) {

        (self as &mut ScopedSection<T>).push(v);

    }

}

/// Consumes a domain-name identifier: identifiers separated by a dot. For

/// simplification of later parsing and span identification the domain-name may

/// contain whitespace, but must reside on the same line.

pub(crate) fn consume_domain_ident<'a>(

    source: &'a InputSource, iter: &mut TokenIter

) -> Result<(&'a [u8], InputSpan), ParseError> {

    let (_, mut span) = consume_ident(source, iter)?;

    while let Some(TokenKind::Dot) = iter.next() {

        iter.consume();

        let (_, new_span) = consume_ident(source, iter)?;

        span.end = new_span.end;

    }

    // Not strictly necessary, but probably a reasonable restriction: this

    // simplifies parsing of module naming and imports.

    if span.begin.line != span.end.line {

        return Err(ParseError::new_error_str_at_span(source, span, "module names may not span multiple lines"));

    }

    // If module name consists of a single identifier, then it may not match any

    // of the reserved keywords

    let section = source.section_at_pos(span.begin, span.end);

    if is_reserved_keyword(section) {

        return Err(ParseError::new_error_str_at_span(source, span, "encountered reserved keyword"));

    }

    Ok((source.section_at_pos(span.begin, span.end), span))

}

/// Consumes a specific expected token. Be careful to only call this with tokens

/// that do not have a variable length.

pub(crate) fn consume_token(source: &InputSource, iter: &mut TokenIter, expected: TokenKind) -> Result<InputSpan, ParseError> {

    if Some(expected) != iter.next() {

        return Err(ParseError::new_error_at_pos(

            source, iter.last_valid_pos(),

            format!("expected '{}'", expected.token_chars())

        ));

    }

    let span = iter.next_span();

    iter.consume();

    Ok(span)

}

/// Consumes a comma separated list until the closing delimiter is encountered

pub(crate) fn consume_comma_separated_until<T, F, E>(

    close_delim: TokenKind, source: &InputSource, iter: &mut TokenIter, ctx: &mut PassCtx,

    mut consumer_fn: F, target: &mut E, item_name_and_article: &'static str,

    close_pos: Option<&mut InputPosition>

) -> Result<(), ParseError>

    where F: FnMut(&InputSource, &mut TokenIter, &mut PassCtx) -> Result<T, ParseError>,

          E: Extendable<Value=T>

{

    let mut had_comma = true;

    let mut next;

    loop {

        next = iter.next();

        if Some(close_delim) == next {

            if let Some(close_pos) = close_pos {

                // If requested return the position of the closing delimiter

                let (_, new_close_pos) = iter.next_positions();

                *close_pos = new_close_pos;

            }

            iter.consume();

            break;

        } else if !had_comma || next.is_none() {

            return Err(ParseError::new_error_at_pos(

                source, iter.last_valid_pos(),

                format!("expected a '{}', or {}", close_delim.token_chars(), item_name_and_article)

            ));

        }

        let new_item = consumer_fn(source, iter, ctx)?;

        target.push(new_item);

        next = iter.next();

        had_comma = next == Some(TokenKind::Comma);

        if had_comma {

            iter.consume();

        }

    }

    Ok(())

}

/// Consumes a comma-separated list of items if the opening delimiting token is

/// encountered. If not, then the iterator will remain at its current position.

/// Note that the potential cases may be:

/// - No opening delimiter encountered, then we return `false`.

/// - Both opening and closing delimiter encountered, but no items.

/// - Opening and closing delimiter encountered, and items were processed.

/// - Found an opening delimiter, but processing an item failed.

pub(crate) fn maybe_consume_comma_separated<T, F, E>(

    open_delim: TokenKind, close_delim: TokenKind, source: &InputSource, iter: &mut TokenIter, ctx: &mut PassCtx,

    consumer_fn: F, target: &mut E, item_name_and_article: &'static str,

    close_pos: Option<&mut InputPosition>

) -> Result<bool, ParseError>

    where F: FnMut(&InputSource, &mut TokenIter, &mut PassCtx) -> Result<T, ParseError>,

          E: Extendable<Value=T>

{

    if Some(open_delim) != iter.next() {

        return Ok(false);

    }

    // Opening delimiter encountered, so must parse the comma-separated list.

    iter.consume();

    consume_comma_separated_until(close_delim, source, iter, ctx, consumer_fn, target, item_name_and_article, close_pos)?;

    Ok(true)

}

pub(crate) fn maybe_consume_comma_separated_spilled<F: FnMut(&InputSource, &mut TokenIter, &mut PassCtx) -> Result<(), ParseError>>(

    open_delim: TokenKind, close_delim: TokenKind, source: &InputSource,

    iter: &mut TokenIter, ctx: &mut PassCtx,

    mut consumer_fn: F, item_name_and_article: &'static str

) -> Result<bool, ParseError> {

    let mut next = iter.next();

    if Some(open_delim) != next {

        return Ok(false);

    }

    iter.consume();

    let mut had_comma = true;

    loop {

        next = iter.next();

        if Some(close_delim) == next {

            iter.consume();

            break;

        } else if !had_comma {

            return Err(ParseError::new_error_at_pos(

                source, iter.last_valid_pos(),

                format!("expected a '{}', or {}", close_delim.token_chars(), item_name_and_article)

            ));

        }

        consumer_fn(source, iter, ctx)?;

        next = iter.next();

        had_comma = next == Some(TokenKind::Comma);

        if had_comma {

            iter.consume();

        }

    }

    Ok(true)

}

/// Consumes a comma-separated list and expected the opening and closing

/// characters to be present. The returned array may still be empty

pub(crate) fn consume_comma_separated<T, F, E>(

    open_delim: TokenKind, close_delim: TokenKind, source: &InputSource,

    iter: &mut TokenIter, ctx: &mut PassCtx,

    consumer_fn: F, target: &mut E, item_name_and_article: &'static str,

    list_name_and_article: &'static str, close_pos: Option<&mut InputPosition>

) -> Result<(), ParseError>

    where F: FnMut(&InputSource, &mut TokenIter, &mut PassCtx) -> Result<T, ParseError>,

          E: Extendable<Value=T>

{

    let first_pos = iter.last_valid_pos();

    match maybe_consume_comma_separated(

        open_delim, close_delim, source, iter, ctx, consumer_fn, target,

        item_name_and_article, close_pos

    ) {

        Ok(true) => Ok(()),

        Ok(false) => {

            return Err(ParseError::new_error_at_pos(

                source, first_pos,

                format!("expected {}", list_name_and_article)

            ));

        },

        Err(err) => Err(err)

    }

}

/// Consumes an integer literal, may be binary, octal, hexadecimal or decimal,

/// and may have separating '_'-characters.

/// TODO: @Cleanup, @Performance

pub(crate) fn consume_integer_literal(source: &InputSource, iter: &mut TokenIter, buffer: &mut String) -> Result<(u64, InputSpan), ParseError> {

    if Some(TokenKind::Integer) != iter.next() {

        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected an integer literal"));

    }

    let integer_span = iter.next_span();

    iter.consume();

    let integer_text = source.section_at_span(integer_span);

    // Determine radix and offset from prefix

    let (radix, input_offset, radix_name) =

        if integer_text.starts_with(b"0b") || integer_text.starts_with(b"0B") {

            // Binary number

            (2, 2, "binary")

        } else if integer_text.starts_with(b"0o") || integer_text.starts_with(b"0O") {

            // Octal number

            (8, 2, "octal")

        } else if integer_text.starts_with(b"0x") || integer_text.starts_with(b"0X") {

            // Hexadecimal number

            (16, 2, "hexadecimal")

        } else {

            (10, 0, "decimal")

        };

    // Take out any of the separating '_' characters

    buffer.clear();

    for char_idx in input_offset..integer_text.len() {

        let char = integer_text[char_idx];

        if char == b'_' {

            continue;

        }

        if !((char >= b'0' && char <= b'9') || (char >= b'A' && char <= b'F') || (char >= b'a' || char <= b'f')) {

            return Err(ParseError::new_error_at_span(

                source, integer_span,

                format!("incorrectly formatted {} number", radix_name)

            ));

        }

        buffer.push(char::from(char));

    }

    // Use the cleaned up string to convert to integer

    match u64::from_str_radix(&buffer, radix) {

        Ok(number) => Ok((number, integer_span)),

        Err(_) => Err(ParseError::new_error_at_span(

            source, integer_span,

            format!("incorrectly formatted {} number", radix_name)

        )),

    }

}

/// Consumes a character literal. We currently support a limited number of

/// backslash-escaped characters

pub(crate) fn consume_character_literal(

    source: &InputSource, iter: &mut TokenIter

) -> Result<(char, InputSpan), ParseError> {

    if Some(TokenKind::Character) != iter.next() {

        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected a character literal"));

    }

    let span = iter.next_span();

    iter.consume();

    let char_text = source.section_at_span(span);

    if !char_text.is_ascii() {

        return Err(ParseError::new_error_str_at_span(

            source, span, "expected an ASCII character literal"

        ));

    }

    match char_text.len() {

        0 => return Err(ParseError::new_error_str_at_span(source, span, "too little characters in character literal")),

        1 => {

            // We already know the text is ascii, so just throw an error if we have the escape

            // character.

            if char_text[0] == b'\\' {

                return Err(ParseError::new_error_str_at_span(source, span, "escape character without subsequent character"));

            }

            return Ok((char_text[0] as char, span));

        },

        2 => {

            if char_text[0] == b'\\' {

                let result = parse_escaped_character(source, span, char_text[1])?;

                return Ok((result, span))

            }

        },

        _ => {}

    }

    return Err(ParseError::new_error_str_at_span(source, span, "too many characters in character literal"))

}

/// Consumes a string literal. We currently support a limited number of

/// backslash-escaped characters. Note that the result is stored in the

/// buffer.

pub(crate) fn consume_string_literal(

    source: &InputSource, iter: &mut TokenIter, buffer: &mut String

) -> Result<InputSpan, ParseError> {

    if Some(TokenKind::String) != iter.next() {

        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected a string literal"));

    }

    buffer.clear();

    let span = iter.next_span();

    iter.consume();

    let text = source.section_at_span(span);

    if !text.is_ascii() {

        return Err(ParseError::new_error_str_at_span(source, span, "expected an ASCII string literal"));

    }

    debug_assert_eq!(text[0], b'"'); // here as kind of a reminder: the span includes the bounding quotation marks

    debug_assert_eq!(text[text.len() - 1], b'"');

    buffer.reserve(text.len() - 2);

    let mut was_escape = false;

    for idx in 1..text.len() - 1 {

        let cur = text[idx];

        if was_escape {

            let to_push = parse_escaped_character(source, span, cur)?;

            buffer.push(to_push);

        } else {

            buffer.push(cur as char);

        }

            was_escape = false;

        } else {

        }

    }

    debug_assert!(!was_escape); // because otherwise we couldn't have ended the string literal

    Ok(span)

}

fn parse_escaped_character(source: &InputSource, literal_span: InputSpan, v: u8) -> Result<char, ParseError> {

    let result = match v {

        b'r' => '\r',

        b'n' => '\n',

        b't' => '\t',

        b'0' => '\0',

        b'\\' => '\\',

        b'\'' => '\'',

        b'"' => '"',

        v => {

            let msg = if v.is_ascii_graphic() {

                format!("unsupported escape character '{}'", v as char)

            } else {

                format!("unsupported escape character with (unsigned) byte value {}", v)

            };

            return Err(ParseError::new_error_at_span(source, literal_span, msg))

        },

    };

    Ok(result)

}

pub(crate) fn consume_pragma<'a>(source: &'a InputSource, iter: &mut TokenIter) -> Result<(&'a [u8], InputPosition, InputPosition), ParseError> {

    if Some(TokenKind::Pragma) != iter.next() {

        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected a pragma"));

    }

    let (pragma_start, pragma_end) = iter.next_positions();

    iter.consume();

    Ok((source.section_at_pos(pragma_start, pragma_end), pragma_start, pragma_end))

}

pub(crate) fn has_ident(source: &InputSource, iter: &mut TokenIter, expected: &[u8]) -> bool {

    peek_ident(source, iter).map_or(false, |section| section == expected)

}

pub(crate) fn peek_ident<'a>(source: &'a InputSource, iter: &mut TokenIter) -> Option<&'a [u8]> {

    if Some(TokenKind::Ident) == iter.next() {

        let (start, end) = iter.next_positions();

        return Some(source.section_at_pos(start, end))

    }

    None

}

/// Consumes any identifier and returns it together with its span. Does not

/// check if the identifier is a reserved keyword.

pub(crate) fn consume_any_ident<'a>(

    source: &'a InputSource, iter: &mut TokenIter

) -> Result<(&'a [u8], InputSpan), ParseError> {

    if Some(TokenKind::Ident) != iter.next() {

        return Err(ParseError::new_error_str_at_pos(source, iter.last_valid_pos(), "expected an identifier"));

    }

    let (ident_start, ident_end) = iter.next_positions();

    iter.consume();

    Ok((source.section_at_pos(ident_start, ident_end), InputSpan::from_positions(ident_start, ident_end)))

}

/// Consumes a specific identifier. May or may not be a reserved keyword.

pub(crate) fn consume_exact_ident(source: &InputSource, iter: &mut TokenIter, expected: &[u8]) -> Result<InputSpan, ParseError> {

    let (ident, pos) = consume_any_ident(source, iter)?;

    if ident != expected {

        debug_assert!(expected.is_ascii());

        return Err(ParseError::new_error_at_pos(

            source, iter.last_valid_pos(),

            format!("expected the text '{}'", &String::from_utf8_lossy(expected))

        ));

    }

    Ok(pos)

}

/// Consumes an identifier that is not a reserved keyword and returns it

/// together with its span.

pub(crate) fn consume_ident<'a>(

    source: &'a InputSource, iter: &mut TokenIter

) -> Result<(&'a [u8], InputSpan), ParseError> {

    let (ident, span) = consume_any_ident(source, iter)?;

    if is_reserved_keyword(ident) {

        return Err(ParseError::new_error_str_at_span(source, span, "encountered reserved keyword"));

    }

    Ok((ident, span))

}

/// Consumes an identifier and immediately intern it into the `StringPool`

pub(crate) fn consume_ident_interned(

    source: &InputSource, iter: &mut TokenIter, ctx: &mut PassCtx

) -> Result<Identifier, ParseError> {

    let (value, span) = consume_ident(source, iter)?;

    let value = ctx.pool.intern(value);

    Ok(Identifier{ span, value })

}

fn is_reserved_definition_keyword(text: &[u8]) -> bool {

    match text {

        KW_STRUCT | KW_ENUM | KW_UNION | KW_FUNCTION | KW_PRIMITIVE | KW_COMPOSITE => true,

        _ => false,

    }

}

fn is_reserved_statement_keyword(text: &[u8]) -> bool {

    match text {

        KW_IMPORT | KW_AS |

        KW_STMT_CHANNEL | KW_STMT_IF | KW_STMT_WHILE |

        KW_STMT_BREAK | KW_STMT_CONTINUE | KW_STMT_GOTO | KW_STMT_RETURN |

        KW_STMT_SYNC | KW_STMT_NEW => true,

        _ => false,

    }

}

fn is_reserved_expression_keyword(text: &[u8]) -> bool {

    match text {

        KW_LET | KW_CAST |

        KW_LIT_TRUE | KW_LIT_FALSE | KW_LIT_NULL |

        KW_FUNC_GET | KW_FUNC_PUT | KW_FUNC_FIRES | KW_FUNC_CREATE | KW_FUNC_ASSERT | KW_FUNC_LENGTH => true,

        _ => false,

    }

}

fn is_reserved_type_keyword(text: &[u8]) -> bool {

    match text {

        KW_TYPE_IN_PORT | KW_TYPE_OUT_PORT | KW_TYPE_MESSAGE | KW_TYPE_BOOL |

        KW_TYPE_UINT8 | KW_TYPE_UINT16 | KW_TYPE_UINT32 | KW_TYPE_UINT64 |

        KW_TYPE_SINT8 | KW_TYPE_SINT16 | KW_TYPE_SINT32 | KW_TYPE_SINT64 |

        KW_TYPE_CHAR | KW_TYPE_STRING |

        KW_TYPE_INFERRED => true,

        _ => false,

    }

}

fn is_reserved_keyword(text: &[u8]) -> bool {

    return

        is_reserved_definition_keyword(text) ||

        is_reserved_statement_keyword(text) ||

        is_reserved_expression_keyword(text) ||

        is_reserved_type_keyword(text);

}

pub(crate) fn seek_module(modules: &[Module], root_id: RootId) -> Option<&Module> {

    for module in modules {

        if module.root_id == root_id {

            return Some(module)

        }

    }

    return None

}

/// Constructs a human-readable message indicating why there is a conflict of

/// symbols.

// Note: passing the `module_idx` is not strictly necessary, but will prevent

// programmer mistakes during development: we get a conflict because we're

// currently parsing a particular module.

pub(crate) fn construct_symbol_conflict_error(

    modules: &[Module], module_idx: usize, ctx: &PassCtx, new_symbol: &Symbol, old_symbol: &Symbol

) -> ParseError {

    let module = &modules[module_idx];

    let get_symbol_span_and_msg = |symbol: &Symbol| -> (String, Option<InputSpan>) {

        match &symbol.variant {

            SymbolVariant::Module(module) => {

                let import = &ctx.heap[module.introduced_at];

                return (

                    format!("the module aliased as '{}' imported here", symbol.name.as_str()),

                    Some(import.as_module().span)

                );

            },

            SymbolVariant::Definition(definition) => {

                if definition.defined_in_module.is_invalid() {

                    // Must be a builtin thing

                    return (format!("the builtin '{}'", symbol.name.as_str()), None)

                } else {

                    if let Some(import_id) = definition.imported_at {

                        let import = &ctx.heap[import_id];

                        return (

                            format!("the type '{}' imported here", symbol.name.as_str()),

                            Some(import.as_symbols().span)

                        );

                    } else {

                        // This is a defined symbol. So this must mean that the

                        // error was caused by it being defined.

                        debug_assert_eq!(definition.defined_in_module, module.root_id);

                        return (

                            format!("the type '{}' defined here", symbol.name.as_str()),

                            Some(definition.identifier_span)

                        )

                    }

                }

            }

        }

    };

    let (new_symbol_msg, new_symbol_span) = get_symbol_span_and_msg(new_symbol);

    let (old_symbol_msg, old_symbol_span) = get_symbol_span_and_msg(old_symbol);

    let new_symbol_span = new_symbol_span.unwrap(); // because new symbols cannot be builtin

    match old_symbol_span {

        Some(old_symbol_span) => ParseError::new_error_at_span(

            &module.source, new_symbol_span, format!("symbol is defined twice: {}", new_symbol_msg)

        ).with_info_at_span(

            &module.source, old_symbol_span, format!("it conflicts with {}", old_symbol_msg)

        ),

        None => ParseError::new_error_at_span(

            &module.source, new_symbol_span,

            format!("symbol is defined twice: {} conflicts with {}", new_symbol_msg, old_symbol_msg)

        )

    }

}