Franklyn Turbak, Allyn Dimock, Robert Muller, and J. B. Wells.
<b>Compiling with Polymorphic and Polyvariant Flow Types</b>.
<i>ACM SIGPLAN Workshop on Types in Compilation (TIC '97)</i>,
June, 1997.<hr>Optimizing compilers for function-oriented and object-oriented languages
exploit type and flow information for efficient implementation.
Although type and flow information (both control and
data flow) are inseparably intertwined, compilers usually compute
and represent them separately.
Partially, this has been a result of the usual polymorphic type systems
using forall and exists quantifiers, which are difficult to use in
combination with flow annotations.
<p>
In the Church Project, we are experimenting with intermediate
languages that integrate type and flow information into a single
<i>flow type</i> framework.  This 
integration facilitates the preservation of flow and type information 
through program transformations.  In this paper we describe&lambda;<sup>CIL</sup>, an intermediate language supporting polymorphic types and polyvariant
flow information and describe its application in program optimiziation.
We are experimenting with this intermediate language in a flow and
type-directed compiler for a functional language.  The types of&lambda;<sup>CIL</sup>encode flow information (1) via labels that approximate
sources and sinks of values and (2) via intersection and union types,
finitary versions of universal and existential types that support type
polymorphism and (in combination with the labels) polyvariant flow
analysis.  Accurate flow types expose opportunities for a wide range
of optimizing program transformations.<hr>[<a href="tic97.ps">PS</a>]  [<a href="tic97.pdf">PDF</a>]