[type]
Parser

[grammar]
grammar T;
s
@init {
<BuildParseTrees()>
}
@after {
<ToStringTree("$r.ctx"):writeln()>
}
  : r=a ;
a : b 'x'
  ;
b : 'y'
  ;

[start]
s

[input]
yx

[output]
"""(a (b y) x)
"""