What is the current state of the law on retroactively interpreting legislation?

The general rule is that barring any express provision stating otherwise, legislation is to be interpreted as having a prospective effect. Courts have only interpreted legislation retroactively in narrow circumstances, where the legislation expressly provides or necessarily implies such an interpretation, for example where the purpose and intent of the legislation clearly demands a retroactive interpretation or where not to apply a retroactive interpretation would lead to an absurd result: see Healey v. Quebec (Attorney-General), 1987 CanLII 80 (SCC), [1987] 1 S.C.R. 158.