Type synonyms and Trex

[John Hughes]

The following program

        type A = (a :: Integer)
        x = (a=2) :: Rec A

produces the error message

        ERROR "Junk.hs" (line 2): Type error in type annotation
        *** Term           : (a=2)
        *** Type           : Rec (a :: a)
        *** Does not match : Rec A
        *** Because        : rows are not compatible

which is strange to say the least!

It seems that synonym definitions for rows are accepted, but are not unfolded
during type checking.

John Hughes