(CommandList
  children: [
    (C {(echo)} {(SQ <'--- pgrphack insists on an argument'>)})
    (Sentence child:(C {(pgrphack)}) terminator:<Op_Semi ';'>)
    (C {(echo)} {($ VSub_QMark '$?')})
    (C {(echo)} {(SQ <'--- pgrphack complains if it cannot run program'>)})
    (Sentence child:(C {(pgrphack)} {(./nonexistent)}) terminator:<Op_Semi ';'>)
    (C {(echo)} {($ VSub_QMark '$?')})
    (C {(echo)} {(SQ <'--- pgrphack runs a program'>)})
    (Sentence child:(C {(pgrphack)} {(echo)} {(ok)}) terminator:<Op_Semi ';'>)
    (C {(echo)} {($ VSub_QMark '$?')})
  ]
)