I also recently created a pretty printer library (https://github.com/calebzulawski/hippo https://github.com/calebzulawski/hippo). In some ways they are similar

I also recently created a pretty printer library (https://github.com/calebzulawski/hippo https://github.com/calebzulawski/hippo). In some ways they are similar, though I felt it was valuable to avoid using ostreams at all, and store indentation levels separately from the printed string. Additionally, I think reflection macros are especially helpful for creating printers for user-defined types.