This is a straightforward verifier for Metamath files written in Lean 4, a dependently typed functional programming language. As of this writing it will compile set.mm in around 10 seconds.

To compile the verifier, you need to acquire lean, and it is recommended to use elan. Once you have it, you should be able to run

lake build

and it will produce the binary as .lake/build/bin/mm-lean4, which can be run as:

lake exe mm-lean4 path/to/set.mm
# or
.lake/build/bin/mm-lean4 path/to/set.mm

to compile set.mm in the current folder.