I don't have a macroexpand function and the self-imposed limit on the number of primitive functions (32 language-related + 16 OS-related) has already been reach

I don't have a macroexpand function and the self-imposed limit on the number of primitive functions (32 language-related + 16 OS-related) has already been reached! Having a whitelist for macros whose expansion should be traced would be good as there's a lot of noise. "Non-intrusive" tracing of any expression can be done, using an @ prefix, based on this: (extend-parser "@" (mac (x) `(let once ,x (seq (eprintln "TRACE: " once) once)))) e.g. (def third (div 100.0 3.0)) => TRUE (add @(mul third 2.0) third) TRACE: 66.66666666666667 => 100.0 That's a good point that you mention tracing needing to be toggleable - it'd be nice to be able to leave all the @s in code. I guess the macro for "@" could either be conditionally replaced with an effective no-op, or it could internally check for the existence of (or truthiness of) a global tracing-enabled definition.