say .parse: '"a {"b {1 + 2}"} d {(1, 10]}"' given grammar one-expression-per-line-or-direct-embed-in-a-string { rule TOP { [ <expr> \n* ]* } token ws { <!ww> \h* } rule expr { <value> [ <op> <value> ]? | <l> <value:<num>> * % ',' <r> } token op { '+' } proto token value {*} token value:<num> { \d+ } token value:<str> { '"' [ '{' <expr> '}' | <-["]> ]* '"' } token l { '(' | '[' } token r { ')' | ']' } }