public Expression ParseExpression(int precedence = 0)
{
var token = Take();
IPrefixParselet prefix;
IInfixParselet infix;
if (!PrefixParselets.TryGetValue(token.ID, out prefix))
{
throw new RantException(_src, token, "Invalid expression '\{token.Value}'.");
}
var left = prefix.Parse(this, token);
// Break when the next token's precedence is less than or equal to the current precedence
// This will assure that higher precedence operations like multiplication are parsed before lower operations.
while (GetPrecedence() > precedence)
{
token = Take();
if (!InfixParselets.TryGetValue(token.ID, out infix))
{
throw new RantException(_src, token, "Invalid operator '\{token.Value}'.");
}
// Replace the left expression with the next parsed expression.
left = infix.Parse(this, left, token);
}
return(left);
}
/// <summary>
/// Returns the precedence of the next infix operator, or 0 if there is none.
/// </summary>
/// <returns></returns>
private int GetPrecedence()
{
if (_pos == _tokens.Length)
{
return(0);
}
IInfixParselet infix;
InfixParselets.TryGetValue(Peek().ID, out infix);
return(infix?.Precedence ?? 0);
}