# non-context free language a^n b^n c^n parsed using Externaltype

!
! /* (i32,i32) defaults to (0,0), used to form two-counter automaton. */

absyntype bool
externtype (i32,i32)
nonterminals A B C AB S
terminals a b c
topsym S

S --> AB:@ok@ C { let (an,bn)=parser.exstate; println!("counters at end: an {}, bn {}",an,bn); ok && bn==0 }

AB --> A B { let (an,bn)=parser.exstate; if an!=bn {parser.abort("different numbers of a's and b's");} an==bn }

A --> A a  { parser.exstate.0+=1; true }
A -->     
B --> B b  { parser.exstate.1+=1; true }
B -->
C --> C c  { parser.exstate.1-=1; true }
C -->