GSOL: A Confluence Checker for Haskell Rewrite Rules

Abstract

We present a tool GSOL, a confluence checker for GHC. It checks the confluence property for rewrite rules in a Haskell program by using the confluence checker SOL (Second-Order Laboratory). The Glasgow Haskell Compiler (GHC) allows programmers to use rewrite rules to optimize Haskell programs in the compilation pipeline. Currently, GHC does not check the confluence of the user-defined rewrite rules. If the rewrite rules are not confluent then the optimization using these rules may produce unexpected results. Therefore, checking the confluence of rewrite rules is important. We implement GSOL using the plugin mechanism of GHC. and provide three usages. We demonstrate confluence checking in the Arrow library.