idris-0.1.7: lib/bool.idr

data Bool = True | False;

not : Bool -> Bool;
not True = False;
not False = True;

%transform not (not ?x) => ?x;

if_then_else : Bool -> |(t:A) -> |(e:A) -> A;
if_then_else True t f = t;
if_then_else False t f = f;

data so : Bool -> Set where oh : so True;

infixl 4 &&,||;

(||) : Bool -> Bool -> Bool;
(||) False x = x;
(||) True _ = True;

(&&) : Bool -> Bool -> Bool;
(&&) True x = x;
(&&) False _ = False;

or_commutes : (x:Bool) -> (y:Bool) -> ((x || y) = (y || x));
or_commutes True False  = refl _;
or_commutes True True   = refl _;
or_commutes False False = refl _;
or_commutes False True  = refl _;

and_commutes : (x:Bool) -> (y:Bool) -> ((x && y) = (y && x));
and_commutes True False  = refl _;
and_commutes True True   = refl _;
and_commutes False False = refl _;
and_commutes False True  = refl _;