Mike Gunter wrote:
I had hoped the "History of Haskell" paper would answer a question I've pondered for some time: why does Haskell have the if-then-else syntax? The paper doesn't address this. What's the story?
thanks, -m
Thanks for asking about this -- it probably should be in the paper. Dan Doel's answer is closest to the truth: I imagine the answer is that having the syntax for it looks nicer/is clearer. "if a b c" could be more cryptic than "if a then b else c" for some values of a, b and c. except that there was also the simple desire to conform to convention here (I don't recall fewer parentheses being a reason for the choice). In considering the alternative, I remember the function "cond" being proposed instead of "if", in deference to Scheme and to avoid confusion with people's expectations regarding "if". A related issue is why Haskell does not have a "single arm" conditional -- i.e. an "if-then" form, which would evaluate to bottom (i.e. error) if the predicate were false. This was actually discussed, but rejected as a bad idea for a purely functional language. -Paul