As a heads-up, the expression interpreter under src\System.Management.Automation\engine\interpreter seems to be a clone from the original code in the DLR. Many improvements to it were made in the CoreFx repo at http://github.com/dotnet/corefx. It'd be good to consider either porting these changes or eliminating the copy altogether once the Compile(bool preferInterpretation) overload is available on all platforms by PowerShell. Note that the regular Compile() overload will be available on all platforms that support System.Linq.Expressions and will use the interpreter in case the compiler is not available.