Gold

Gold is a free parsing system compatible with FreePascal that you can use to develop your own programming languages, scripting languages, interpreters, and all kind of parsers and expression analyzers. It uses LALR parsing, and a mix of BNF notation, character sets and regular expressions for terminals to define language grammars. Code and grammar are separated, so grammar is not tied to implementation language. This means that the same grammar can be loaded into engines made in different programming languages.

There is a subjective feature comparison table of several parsers on Gold site, with special attention to Gold vs Yacc comparison.

Gold Parser Builder

GOLD Parser Builder can be used to create, modify and test languages in Windows IDE (which runs on Wine). Command line tools are also available.

Features:

• Grammar editor with syntax highlighting.
• Grammar-generating wizard.
• Test window to step through parsing of a sample source.
• Templating system that can generate lexers/parsers or skeleton programs for various languages (including Delphi and FreePascal).
• Importing/exporting YACC/Bison format. Exporting XML and HTML format.
• Interactive inspection of the compiled DFA and LALR tables.

Importing YACC/BISON can be very picky, so you will probably have to convert linux line endings and delete most of the not needed code leaving just BNF rules. Import from lex file does not exist, so you will have to examine lex file yourself to see if there are terminals that you should manually add to your GOLD grammar.

Gold Engines

Gold Parser Builder has an option to build skeleton application for Delphi and FreePascal from existing grammar. However, there are also user made Gold Engines for FreePascal/Lazarus which can load compiled grammar (CGT file) and parse some file according to loaded grammar.

Gold Parser Builder has changed CGT file format in version 5. CGT v5.0 file format is used for all GOLD Parser Builder versions newer then 5.0.0 (including 5.2.0 which is actual at the moment of writing this text), and CGT v1.0 for all older versions. This means that with older engines you will need to use older Gold Parser Builder. You can find old v3.4.4 version here.

Lazarus Gold Engine 2018

This is a refactored cross platform Delphi engine used for JSON parsing example. It supports only CGT v1.0 file format so you need to use older Gold Parser Builder with it. You can find it here.

Gold Parser for Lazarus

Another adaptation of the same Delphi engine for Lazarus. It's a little more commented then the 2018 version so it might be more appealing to the ones who want to understand the code. It also supports only CGT v1.0 file format so you need to use older Gold Parser Builder. You can find the engine here.

GOLD Parser for Free Pascal and Lazarus

There are 2 versions. One derived from the same old Delphi engine compatible with CGT v1.0, and the new one translated from Java which is compatible with both CGT v1.0 and CGT v5.0. This means that it will load grammars compiled with latest version of Gold Parser Builder (v5.2.0 at the moment of writing). This engine was used for Pascal parsing example. The engine can be found here.

Goldie

Although Goldie is not originaly made for use with Pascal, it has many command line tools which can be useful to manipulate CGT files (Gold compiled grammar). You can show CGT file in human readable format, compile grammar to CGT file without Gold Parser Builder executable, and parse source according to some CGT file to save the resulting tokens and parsed tree to JSON file.

Examples

We will load pascal grammar into Gold Parser Builder 5.2, compile grammar to produce CGT file, load that CGT file into Lazarus Gold Engine (version compatible with Gold 5.20), and parse our pascal sample source code.

Pascal example

Pascal Grammar

Pascal grammar is big, so you will need to expand it with the shown linked button on the right.

! ---------------------------------------------------------------------------------
! Standard Pascal Grammar
!
! modified by Avra (Zeljko Avramovic) for compatibility with latest version of Gold
! ---------------------------------------------------------------------------------

"Name"                    =   'Pascal' 
"Version"                 =   '1973'
"Author"                  =   'Niklaus Wirth' 
"About"                   =   'PASCAL was developed by NIKLAUS WIRTH of the ETH Technical Institute of Zuerich in 1970-1971.(published in 1973)'

"Case Sensitive"          =   False
"Start Symbol"            =   <Program>
                 
Comment Start             =   '{'
Comment End               =   '}'
Comment Line              =   '//'

{Hex Digit}               =   {Digit} + [ABCDEF]

{Id Head}                 =   {Letter} + [_]
{Id Tail}                 =   {Id Head} + {Digit}

{String Ch}               =   {Printable} - ['']
{Char Ch}                 =   {Printable} - ['']

DecLiteral                =   [123456789]{digit}*
HexLiteral                =   '$'{Hex Digit}+
FloatLiteral              =   {Digit}*'.'{Digit}+

StringLiteral             =   ''( {String Ch} | '\'{Printable} )* ''
CharLiteral               =   '' ( {Char Ch} | '\'{Printable} )''

id                        =   {Id Head}{Id Tail}*

<constant>                ::= DecLiteral
                          |   StringLiteral
                          |   FloatLiteral
                          |   HexLiteral
                          |   CharLiteral


!=========================================== Program


<Program>                 ::= <ProgramHeader> <Declarations> <CompoundStatement> '.'

<ProgramHeader>           ::= PROGRAM id ';'
                          |   PROGRAM id '(' <IdList> ')' ';'

<Declarations>            ::= <ConstantDefinitions> <TypeDefinitions> <VariableDeclarations> <ProcedureDeclarations>

<ConstantDefinitions>     ::= CONST <ConstantDefinitionList>
                          |  

<ConstantDefinitionList>  ::= <ConstantDef>
                          |   <ConstantDef> <ConstantDefinitionList>

<ConstantDef>             ::= id '=' <constant> ';'

<TypeDefinitions>         ::= TYPE <TypeDefinitionList>
                          |

<TypeDefinitionList>      ::= <TypeDef>
                          |   <TypeDef> <TypeDefinitionList>

<TypeDef>                 ::= id '=' <TypeSpecifier> ';'

<VariableDeclarations>    ::= VAR <VariableDeclarationList>
                          | 

<VariableDeclarationList> ::= <VariableDec>
                          |   <VariableDec> <VariableDeclarationList>

<VariableDec>             ::= <IdList> ':' <TypeSpecifier> ';'

<ProcedureDeclarations>   ::= <ProcedureDec> <ProcedureDeclarations>
                          | 

<ProcedureDec>            ::= <ProcedureHeader> FORWARD ';'
                          | <ProcedureHeader> <Declarations> <CompoundStatement> ';'
                          | <FunctionHeader> FORWARD ';'
                          | <FunctionHeader> <Declarations> <CompoundStatement> ';'

<ProcedureHeader>         ::= PROCEDURE id <Arguments> ';'

<FunctionHeader>          ::= FUNCTION id <Arguments> ':' <TypeSpecifier> ';'

<Arguments>               ::= '(' <ArgumentList> ')'
                          | 

<ArgumentList>            ::= <Arg>
                          |   <Arg> ';' <ArgumentList>

<Arg>                     ::= <IdList> ':' <TypeSpecifier>
                          |   VAR <IdList> ':' <TypeSpecifier>

<CompoundStatement>       ::= BEGIN <StatementList> END

<StatementList>           ::= <Statement>
                          |   <Statement> ';' <StatementList>

<Statement>               ::= <CompoundStatement>
                          |   <AssignmentStatement>
                          |   <ProcedureCall>
                          |   <ForStatement>
                          |   <WhileStatement>
                          |   <IfStatement>
                          |   <CaseStatement>
                          |   <RepeatStatement>
                          | 

<AssignmentStatement>     ::= <Variable> ':=' <Expression>
!                         |   <Variable> ':=' <FunctionCall>

<ProcedureCall>           ::= id <Actuals>

<ForStatement>            ::= FOR id ':=' <Expression> TO <Expression> DO <Statement>
                          |   FOR id ':=' <Expression> DOWNTO <Expression> DO <Statement>

<WhileStatement>          ::= WHILE <Expression> DO <Statement>

<IfStatement>             ::= IF <Expression> THEN <Statement> ELSE <Statement>

<RepeatStatement>         ::= REPEAT <StatementList> UNTIL <Expression>

<CaseStatement>           ::= CASE <Expression> OF <CaseList> END

<CaseList>                ::= <Case>
                          |   <Case> ';' <CaseList>

<Case>                    ::= <ConstantList> ':' <Statement>

<ConstantList>            ::= <constant>
                          |   <constant> ',' <ConstantList>

<Expression>              ::= <SimpleExpression>
                          |   <SimpleExpression> '=' <SimpleExpression>
                          |   <SimpleExpression> '<>' <SimpleExpression>
                          |   <SimpleExpression> '<' <SimpleExpression>
                          |   <SimpleExpression> '<=' <SimpleExpression>
                          |   <SimpleExpression> '>' <SimpleExpression>
                          |   <SimpleExpression> '>=' <SimpleExpression>
                          |   <FunctionCall>

<SimpleExpression>        ::= <Term>
                          |   <SimpleExpression> '+' <Term>
                          |   <SimpleExpression> '-' <Term>
                          |   <SimpleExpression> OR <Term>

<Term>                    ::= <Factor>
                          |   <Term> '*' <Factor>
                          |   <Term> '/' <Factor>
                          |   <Term> 'DIV' <Factor>
                          |   <Term> 'MOD' <Factor>
                          |   <Term> 'AND' <Factor>

<Factor>                  ::= '(' <Expression> ')'
                          |   '+' <Factor>
                          |   '-' <Factor>
                          |   NOT <Factor>
                          |   <constant>
                          |   <Variable>

<FunctionCall>            ::= id <Actuals>

<Actuals>                 ::= '(' <ExpressionList> ')' 

<ExpressionList>          ::= <Expression>
                          |   <Expression> ',' <ExpressionList>
                          |

<Variable>                ::= id
                          |   <Variable> '.' id
                          |   <Variable> '^'
                          |   <Variable> '[' <ExpressionList> ']'

<TypeSpecifier>           ::= id
                          |   '^' <TypeSpecifier>
                          |   '(' <IdList> ')'
                          |   <constant> '..' <constant>
                          |   ARRAY '[' <DimensionList> ']' OF <TypeSpecifier>
                          |   RECORD <FieldList> END
                          |   FILE OF <TypeSpecifier>

<DimensionList>           ::= <Dimension>
                          |   <Dimension> ',' <DimensionList>

<Dimension>               ::= <constant> '..' <constant>
                          |   id

<FieldList>              ::= <Field>
                         |   <Field> ';' <FieldList>

<Field>                  ::= <IdList> ':' <TypeSpecifier>

<IdList>                 ::= id
                         |   id ',' <IdList>

Pascal Source Code

program test; // simple pascal code for testing parser

const
  PI = 3.1415;

var
  a, b, c: real;

procedure hello(s: string; b, c: real);
begin
  writeln(s);
  writeln(b);
  writeln(c);
end;

function square(a: real): real;
begin
  result := a * a;
end;

function half(a: real): real;
begin
  result := a / 2;
end;

function twopi: real;
begin
  result := pi * 2;
end;

begin
  a := PI;
  b := a * 10;
  c := square(half(twopi()));
  hello('Hello World!', b, c);
end.

Download links

• Gold Parser Builder 3.4.4 setup for older engines not compatible with latest Gold 5.x CGT files
• Gold Parser Builder 5.2.0 setup