Ah. I wonder why -1 requires parens. I also thought that you can turn an inline operator into a regular function by putting parens around it. (And vice versa with back ticks). I guess I should do my own Haskell homework instead of asking here. :)
If I remember accurately it is because anything that is not a value in haskell is a function.
So without the parentheses it can't know if -1 means the function - applied to some other value and the number one like1-1( function - applied to 1 and 1 ) or the value -1, so the way they solved it is to have it be the function, therefore you would be missing an argument or you would be passning a wrong type.
When you want a value you would have to use (-1) so then it knows that you trully mean the value -1.
PS: This is my first comment I hope I didn't come out sounding a but too "know it all" or trying to sound smart, I just wanted to explain it the best I can.
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