Kripke-style untyped NbE in racket

An implementation of normalization by evaluation loosely based on A Denotational Account of Untyped Normalization by Evaluation and Abel's thesis on NbE.

Since the implementation is untyped, the normalize function only gives you $\beta$-normal forms. However, you can get a little bit of $\beta\eta$-equivalence by invoking Coquand's algorithm (η-eq?) on $\beta$-normal forms.

I'm hoping to expand the repository into a benchmark suite where I can visualize the performance trade-off of type-directed NbE compared to untyped NbE composed with Coquand's algorithm.