On 23/10/06, Henning Thielemann
Cale Gibbard cgibbard at gmail.com, Sun Oct 22 12:23:18 EDT 2006
The 'then' and 'else' visually separate the parts of the if-expression, and serve to guide one's eyes when reading code silently, and one's words when speaking it aloud.
This argument is true for every function. I don't see why if test then a else b is necessary, but foldr with_function f initial_state i on_list xs not.
If-then-else corresponds to a structural part of the English language. Right folding doesn't. Besides, those are awful names for the parts of a foldr. The first parameter is the cons replacement and the second the nil replacement. Having a general syntax for standard catamorphisms on an algebraic datatype might not be an altogether terrible idea.
If you really need "then" and "else" we could certainly construct some library functions, to let if test `then` a `else` b work, or if (test expression) then (a expression) else (b expression)
Say infixr 0 then, else
data Else a = Else a a
else = Else
and so on ...
That seems fairly weak. Why do you want to break all the Haskell code ever written? Yes, you're proposing to phase it out, but there's a lot of code which isn't actively being maintained that would break, and what you're proposing looks a whole lot worse to (I don't think I'm assuming much) most Haskell programmers. The changes that you've been proposing to Haskell make me wonder why it is that you're interested in working with Haskell in the first place -- it's just not the sort of minimal language you're looking for. Why do we allow multiple function equations when case could be used? Why do we allow guards? Why do we have both let and where? The thing is, if you want to create a function which does the same thing as if-then-else, and use it, you're free to do so. By and large, I think that most people would agree that having the then and else parts clearly delimited in such a common form of expression helps a good deal with reading and writing the code. If using an if' function was beneficial, people would be doing it all the time by now. The syntactic form eliminates excess parentheses, and gives the eye an easy way to follow the logic, whereas with just a function, you have to work harder to match parens before you know what the parts of the expression are.