AoC 2021 day 10 (dc)

#!/usr/bin/dc

[q] sX

# calculate syntax scoring table
3 d 1:s
19* d 2:s
21* d 3:s
21* 4:s

0 ss                    # syntax score = 0

[ lt;s ls+ ss 3Q ] sS   # syntax error: add value from table, exit 3 levels

[ 4- 0 ] sO             # open token: tok exp-stack -> 0 close-tok exp-stack
[ lt !=S ] sC           # close token: (tok != exp-top, syntax) exp-rest

[
    10~ st sl           # line exp-stack -> exp-stack (t = token, l = rest of line)
    lt d 4<O            # exp -> (tok > 4, open) tok exp, open returns: 0 exp
    0!=C                # else ((tok|0) != 0 closed) exp

    ll d 0!=P           # exp -> line exp (loop if line not zero)
] sP

[
    c 0 ? d 0=X         # clear stack, get input line, exit if 0
    rs.                 # remove sentinel zero
    lPx                 # attempt parse
    lMx                 # loop
] sM
lMx

[Part 1: ]n lsp