//
// Helper routine for parsing a code entity from a token stream.
//
// This terminology is mostly legacy from an older implementation of Epoch.
// An entity is really just a branch/flow-control construct such as a loop
// or an if/else statement. Typically there is an expression which controls
// execution and an associated code block.
//
internal static bool ParseEntity(ParseSession parser, LexicalScope parentscope, int starttoken, out int consumedtokens)
{
consumedtokens = starttoken;
int totaltokens = starttoken;
if (parser.CheckToken(totaltokens, "if"))
{
if (!parser.CheckToken(totaltokens + 1, "("))
{
return(false);
}
totaltokens += 2;
var expr = Expression.Parse(parser, totaltokens, out totaltokens);
if (expr == null)
{
throw new SyntaxError("if() statement must be supplied with a valid Boolean-typed expression", parser.ReversePeekToken());
}
while (parser.CheckToken(totaltokens, ")"))
{
++totaltokens;
}
if (!parser.CheckToken(totaltokens, "{"))
{
throw new SyntaxError("if() statement must be followed by a code block surrounded in braces { }", parser.PeekToken(totaltokens));
}
++totaltokens;
LexicalScope.Parse(parser, parentscope, totaltokens, out totaltokens);
while (parser.CheckToken(totaltokens, "elseif"))
{
totaltokens += 2;
var condexpr = Expression.Parse(parser, totaltokens, out totaltokens);
if (condexpr == null)
{
throw new SyntaxError("elseif() statement must be supplied with a valid Boolean-typed expression", parser.ReversePeekToken());
}
while (parser.CheckToken(totaltokens, ")"))
{
++totaltokens;
}
if (!parser.CheckToken(totaltokens, "{"))
{
throw new SyntaxError("elseif() statement must be followed by a code block surrounded in braces { }", parser.PeekToken(totaltokens));
}
++totaltokens;
LexicalScope.Parse(parser, parentscope, totaltokens, out totaltokens);
}
if (parser.CheckToken(totaltokens, "else"))
{
++totaltokens;
if (!parser.CheckToken(totaltokens, "{"))
{
throw new SyntaxError("else statement must be followed by a code block surrounded in braces { }", parser.PeekToken(totaltokens));
}
++totaltokens;
LexicalScope.Parse(parser, parentscope, totaltokens, out totaltokens);
}
consumedtokens = totaltokens;
return(true);
}
else if (parser.CheckToken(totaltokens, "while"))
{
if (!parser.CheckToken(totaltokens + 1, "("))
{
throw new SyntaxError("while() statement must be supplied with a valid Boolean-typed expression", parser.ReversePeekToken());
}
totaltokens += 2;
while (parser.CheckToken(totaltokens, ")"))
{
++totaltokens;
}
var expr = Expression.Parse(parser, totaltokens, out totaltokens);
++totaltokens;
if (!parser.CheckToken(totaltokens, "{"))
{
throw new SyntaxError("while() statement must be followed by a code block surrounded in braces { }", parser.PeekToken(totaltokens));
}
++totaltokens;
LexicalScope.Parse(parser, parentscope, totaltokens, out totaltokens);
consumedtokens = totaltokens;
return(true);
}
return(false);
}