[type]
Parser

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

[start]
s

[input]
z

[output]
"""(a z)
"""

[errors]
"""line 1:0 mismatched input 'z' expecting {'x', 'y'}
"""