static public (SourceCode, string) parse(string code)
{
lexer.Lexer Lexer = lexer.NewLexer(code);
var(sourceCode, error) = parseSourceCode(ref Lexer);
if (error != null)
{
return(sourceCode, error);
}
Lexer.NextTokenIs(lexer.TOKEN_EOF);
return(sourceCode, null);
}
//SourceCode ::= Statement+
static public (SourceCode, string) parseSourceCode(ref lexer.Lexer Lexer)
{
SourceCode sourceCode = new SourceCode();
string error;
sourceCode.LineNum = Lexer.GetLineNum();
(sourceCode.Statements, error) = parseStatements(ref Lexer);
if (error != null)
{
return(sourceCode, error);
}
return(sourceCode, null);
}
//Variable ::= "$" Name Ignored
static public (Variable, string) parseVariable(ref lexer.Lexer Lexer)
{
Variable variable = new Variable();
string error;
variable.LineNum = Lexer.GetLineNum();
Lexer.NextTokenIs(lexer.TOKEN_VAR_PREFIX);
(variable.Name, error) = parseName(ref Lexer);
if (error != null)
{
return(variable, error);
}
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
return(variable, null);
}
static public (Statement, string) parseStatement(ref lexer.Lexer Lexer)
{
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
switch (Lexer.LookAhead())
{
case lexer.TOKEN_PRINT:
return(parsePrint(ref Lexer));
case lexer.TOKEN_VAR_PREFIX:
return(parseAssignment(ref Lexer));
default:
return(null, "parseStatement(): unknown Statement.");
}
}
//Statement ::= Print | Assignment
static public (List <Statement>, string) parseStatements(ref lexer.Lexer Lexer)
{
List <Statement> statements = new List <Statement>();
while (!isSourceCodeEnd(Lexer.LookAhead()))
{
var(statement, error) = parseStatement(ref Lexer);
if (error != null)
{
return(null, error);
}
statements.Add(statement);
}
return(statements, null);
}
//Print ::= "print" "(" Ignored Variable Ignored ")" Ignored
static public (Print, string) parsePrint(ref lexer.Lexer Lexer)
{
Print print = new Print();
string error;
print.LineNum = Lexer.GetLineNum();
Lexer.NextTokenIs(lexer.TOKEN_PRINT);
Lexer.NextTokenIs(lexer.TOKEN_LEFT_PAREN);
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
(print.Variable, error) = parseVariable(ref Lexer);
if (error != null)
{
return(print, error);
}
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
Lexer.NextTokenIs(lexer.TOKEN_RIGHT_PAREN);
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
return(print, null);
}
//Assignment ::= Variable Ignored "=" Ignored String Ignored
static public (Assignment, string) parseAssignment(ref lexer.Lexer Lexer)
{
Assignment assignment = new Assignment();
string error;
assignment.LineNum = Lexer.GetLineNum();
(assignment.Variable, error) = parseVariable(ref Lexer);
if (error != null)
{
return(assignment, error);
}
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
Lexer.NextTokenIs(lexer.TOKEN_EQUAL);
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
(assignment.String, error) = parseString(ref Lexer);
if (error != null)
{
return(assignment, error);
}
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
return(assignment, null);
}
//String ::= '"' '"' Ignored | '"' StringCharacter '"' Ignored
static public (string, string) parseString(ref lexer.Lexer Lexer)
{
string str = "";
switch (Lexer.LookAhead())
{
case lexer.TOKEN_DUOQUOTE:
Lexer.NextTokenIs(lexer.TOKEN_DUOQUOTE);
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
return(str, null);
case lexer.TOKEN_QUOTE:
Lexer.NextTokenIs(lexer.TOKEN_QUOTE);
str = Lexer.scanBeforeToken(lexer.tokenNameMap[lexer.TOKEN_QUOTE]);
Lexer.NextTokenIs(lexer.TOKEN_QUOTE);
Lexer.LookAheadAndSkip(lexer.TOKEN_IGNORED);
return(str, null);
default:
return(null, "parseString(): not a string.");
}
}
//Name ::= [_A-Za-z][_0-9A-Za-z]*
static public (string, string) parseName(ref lexer.Lexer Lexer)
{
var(_, name) = Lexer.NextTokenIs(lexer.TOKEN_NAME);
return(name, null);
}