public IExpression Parse(Parser parser, Token token)
{
var expr = new IfExpression()
{
token = parser.CurrentToken()
};
if (!parser.ExpectPeek(TokenType.LPAREN))
{
return(null);
}
parser.NextToken();
expr.Condition = parser.ParseExpression(BindingPower.LOWEST);
if (!parser.ExpectPeek(TokenType.RPAREN))
{
return(null);
}
if (!parser.ExpectPeek(TokenType.LBRACE))
{
return(null);
}
expr.Consequence = new BlockStatementParslet().Parse(parser);
if (parser.PeekTokenIs(TokenType.ELSE))
{
parser.NextToken();
if (!parser.PeekTokenIs(TokenType.LBRACE) && !parser.PeekTokenIs(TokenType.IF))
{
return(null);
}
if (parser.PeekTokenIs(TokenType.LBRACE))
{
parser.NextToken();
expr.Alternative = new BlockStatementParslet().Parse(parser);
}
else
{
parser.NextToken();
expr.Alternative = parser.ParseExpression(BindingPower.LOWEST);
}
}
return(expr);
}
private IObject EvalIfExpression(IfExpression ie, Environment env)
{
var condition = Eval(ie.Condition, env);
if (condition is Error)
{
return(condition);
}
if (IsTruthy(condition))
{
return(Eval(ie.Consequence, env));
}
else if (ie.Alternative != null)
{
return(Eval(ie.Alternative, env));
}
else
{
return(null);
}
}