# [dc], 39 ?dsiZdsl[r1-d0<m]dsmxklixzll-2%B*C1+P Input string is read from STDIN and should be in the form `[yynynynynyyn]`. dc is not known for its string handling, but we have just enough here to get this to work. The approach here is to count the `n`s, and output `y` if even or `n` if odd. This is done by executing the input string as a macro. `dc` will output `'y' (0171) unimplemented` errors for all the `y`s and attempt to pop strings and print them for all the `n`s. So first we make sure we have plenty (total input string length) of empty strings `` on the stack to pop. Then we execute the input string and see how many `` are left on the stack. The original string length is subtracted from this to give the (-ve) total number of `n`s. The rest is arithmetic to do mod 2 and have the output come out right as ASCII `y` or `n`. ?dsi # Read input string, duplicate, store in register i Zdsl # Get input length, duplicate, store in register l [ ] # define macro to:  # push empty string r # swap empty string and remaining length 1- # subtract 1 from length d0 # duplicate and compare with 0 <m # if >0 recursively call this macro again dsmx # duplicate macro, store in register m and execute k # discard left-over 0 lix # load input string and execute as macro z # get stack length ll- # load string length and subract 2% # mod 2 (result is -ve because difference is -ve) B* # multiply by 11 ('y' - 'n') C1+ # add 121 ('y') P # print result as ASCII char [Try it online!][TIO-jhi0hjr2] [dc]: https://www.gnu.org/software/bc/manual/dc-1.05/html_mono/dc.html [TIO-jhi0hjr2]: https://tio.run/##S0n@/98@pTgzKqU4Jzo6tshQN8XAJjc2pTi3Ijsns6IqJ0fXSNVJy9lQO@D//@jKyjworMyLBQA "dc – Try It Online"