@implicitNotFound("Could not find an implicit instance of Tell[${F}, ${L}]. If you wish\nto capture side-channel output of type ${L} at this location, you may want\nto construct a value of type WriterT for this call-site, rather than ${F}.\nAn example type:\n\n WriterT[${F}, ${L}, *]\n\nOne use-case for this would be if ${L} represents an accumulation of values\nwhich are produced by this function *in addition to* its normal results.\nThis can be used to implement some forms of pure logging.\n\nIf you do not wish to capture a side-channel of type ${L} at this location,\nyou should add an implicit parameter of this type to your function. For\nexample:\n\n (implicit ftell: Tell[${F}, ${L}])\n") trait Tell[F[_], -L] extends Serializable
Tell[F, L] is the ability to "log" values L inside a context F[_], as an effect.
Tell[F, L] is the ability to "log" values L inside a context F[_], as an effect.
Tell has no external laws.
Tell has one internal law:
def writerIsTellAndMap(a: A, l: L) = {
(tell(l) as a) <-> writer(a, l)
}
def tupleIsWriterFlipped(a: A, l: L) = {
writer(a, l) <-> tuple((l, a))
}
- Companion
- object