SOURCE_FILE@0..21
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      IDENT@3..4 "a"
    PARAM_LIST@4..6
      L_PAREN@4..5 "("
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    BLOCK_EXPR@7..20
      L_CURLY@7..8 "{"
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      FN@9..18
        FN_KW@9..11 "fn"
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        NAME@12..13
          IDENT@12..13 "b"
        PARAM_LIST@13..15
          L_PAREN@13..14 "("
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        WHITESPACE@15..16 " "
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          L_CURLY@16..17 "{"
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