The most notable improvement in Haskell 1.3 is its I/O, with a shift to "monadic-style" I/O.
We still offer direct access to the so-called `PrimIO' monad, via the `PreludeGlaST' interface. This is NON-STANDARD, an extension. This interface is described in Section See section Access to the `PrimIO' monad.
The old `PreludePrimIO' interface is DEAD.
The even-older `PreludeGlaIO' interface is DEADER.