F# code quotation invocation, performance, and run-time requirements

Question

Here are 4 deeply related questions about F# code quotations -

How do I invoke an F# code quotation?

Will it be invoked in a manner less efficient than if it were just a plain old F# lambda? to what degree?

Will it require run-time support for advanced reflection or code-emitting functionality (which is often absent or prohibited from embedded platforms I am targeting)?

Answer 1

Quotations are just data, so you can potentially "invoke" them in whatever clever way you come up with. For instance, you can simply walk the tree and interpret each node as you go, though that wouldn't perform particularly well if you're trying use the value many times and its not a simple value (e.g. if you've quoted a lambda that you want to invoke repeatedly).

If you want something more performant (and also simpler), then you can just use Linq.RuntimeHelpers.LeafExpressionConverter.EvaluateQuotation. This doesn't support all possible quotations (just roughly the set equivalent to C# LINQ expressions), and it's got to do a bit more work to actually generate IL, etc., but this should be more efficient if you're reusing the result. This does its work by first converting the quotation to a C# expression tree and then using the standard Compile function defined there, so it will only work on platforms that support that.