The Idea of Lisp
The conditional expression or more specifically everything being an expression is my favorite thing about Lisp. I did not know that McCarthy pushed to add it to Algol which apparently today is the ternary operator for most languages.<p>It is annoying that so many languages (C, Java, C#, etc) have both a conditional statement (if-else) and conditional expression (ternary ?:). Really the if-else should be an expression (I think the ternary operator is hideous).