The latest implementation of Picol has a Tcl-alike [expr] implemented in 40 lines of code that uses Pratt-style parsing: https://github.com/antirez/picol/blob/main/picol.c#L490
I have a Tcl Improvement Proposal (TIP 676) currently being voted on which introduces an alternative compact form of calculation. The implementation uses a Pratt parser: https://core.tcl-lang.org/tcl/file?ci=cgm-equals-command&nam... which directly generates bytecode rather than creating a parse tree.