## MLton 20241230+git20251029+dfsg-5

# XMLSimplifyTypes

XMLSimplifyTypes is an optimization pass for the XML IntermediateLanguage, invoked from XMLSimplify.

## Description

This pass simplifies types in an XML program, eliminating all unused type arguments.

## Implementation

- `simplify-types.sig`

- `simplify-types.fun`

## Details and Notes

It first computes a simple fixpoint on all the `datatype` declarations to determine which `datatype` `tycon` args are actually used. Then it does a single pass over the program to determine which polymorphic declaration type variables are used, and rewrites types to eliminate unused type arguments.

This pass should eliminate any spurious duplication that the Monomorphise pass might perform due to phantom types.