[valisystem]

There's also rustlex [1] that have been around for a while and provides rust stable v1.0 support through syntex [2]. I use it for a handlebars implementation [3].

[1] https://github.com/LeoTestard/rustlex

[2] https://github.com/erickt/rust-syntex

[3] https://github.com/nicolas-cherel/rumblebars