Using functional composition as before, around or after filter. This is a smart use of tap, to compose a sequence of functions that need somekind of sideeffect and provide a clear seperation of pure and impure functions

composition_with_tap

//-- http://allong.es/try/
tap     = allong.es.tap
flip    = allong.es.flip
curry   = allong.es.curry
compose = allong.es.compose
call    = allong.es.call
 
//-- square :: Int -> Int
function square(x) { return x*x }
 
//-- log :: String -> a -> IO ()
function log(msg, value) { console.log(msg, value) }
 
logger       = curry(log) 
tapWith      = flip(tap)
logAndSquare = compose(square, tapWith(logger('Logging this')))

//-- Since allong.es curry functions with `call` it could be written as
logAndSquare = compose(square, tapWith(call(log, 'Logging this')))