// The colour test function returns TRUE or FALSE
var is_sbp = colour => (colour === "sky_blue_pink") ? TRUE : FALSE;

// Store the responses to the colour test as a PAIR
var colourResponses = PAIR(pigs.fly)(elephants.jump);

// Modify HEAD and TAIL to receive a PAIR
var HEAD = pair => pair(TRUE);
var TAIL = pair => pair(FALSE);

// Now HEAD and TAIL can be used in a more intuitive manner
HEAD(colourResponses);    // -> pigs.fly
TAIL(colourResponses);    // -> elephants.jump