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The only parser combinator library I used (smug, for common lisp) had little trouble with breakpoints; (any parse with significant backtracking was annoying but breakpoints worked fine) is it common that one cannot use breakpoints for debugging in other parser-combinator libraries?

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I'm not familiar with Smug, but I would guess that the combinator is implemented using LISP macros which are than expanded into "real" source code (lisp lists) which is evaluated directly and can halt on break points.

In programing languages which do not have true macros The combinator API normally creates a data structure representing the grammar which is than interpreted Which usually makes debugging harder and the parsing slower.

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