oil AST

(command.CommandList
  children: [
    (C {<Id.KW_Set set>} {<-e>})
    (C {<source>} {($ Id.VSub_DollarName '$TRAVIS_BUILD_DIR') </ci/travis_env_common.sh>})
    (C {<git>} {<archive>} {<HEAD>} {<--prefix> <Id.Lit_Equals '='> <apache-arrow/>} 
      {<--output> <Id.Lit_Equals '='> <arrow-src.tar.gz>}
    )
    (C {<./dev/release/run-rat.sh>} {<arrow-src.tar.gz>})
    (C {<pushd>} {($ Id.VSub_DollarName '$CPP_BUILD_DIR')})
    (C {<ctest>} {<-VV>} {<-L>} {<unittest>})
    (C {<popd>})
  ]
)