[flang-dev] Regarding main program structure

[Rajesh K Singh via flang-dev]

Hello,



According to specification R1401, a Fortran main program *must* have an
“end statement” whereas other parts are optional.

// R1401 main-program ->

//         [program-stmt] [specification-part] [execution-part]

//         [internal-subprogram-part] end-program-stmt



Thus, the below case.f90 is a legitimate fortran program:

[user at localhost ~/F18]$ cat -n case.f90

     1  end  !only end-program-stmt is specified.

[user at localhost ~/F18]$



The implementation of MainProgram structure (“lib/parser/parse-tree.h”)
shows that only “ProgramStmt” and “InternalSubprogramPart” are optional.

struct MainProgram {

  TUPLE_CLASS_BOILERPLATE(MainProgram);

  std::tuple<std::optional<Statement<ProgramStmt>>, SpecificationPart,

      ExecutionPart, std::optional<InternalSubprogramPart>,

      Statement<EndProgramStmt>>

      t;

};



Why “SpecificationPart” and “ExecutionPart” are not implemented as optional
(std::optional), while these are optional similar to “ProgramStmt” and
“InternalSubprogramPart”?



Thanks in anticipation.
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