Can Pascal units be compiled as executables?

Question

I like my libraries to double as executables. The desired behavior is:

$ ./scriptedmain
Main: The meaning of life is: 42
$ ./test
Test: The meaning of life is: 42

How can I:

• Get scriptedmain.p to compile into a scriptedmain binary?
• Prevent test.p from running the code that's in scriptedmain.p's begin/end section?

scriptedmain.p:

unit ScriptedMain;
    interface

    function MeaningOfLife () : integer;

    implementation

    function MeaningOfLife () : integer;
    begin
        MeaningOfLife := 42
    end;
begin
    write('Main: The meaning of life is: ');
    writeln(MeaningOfLife())
end.

When I compile scriptedmain.p with fpc scriptedmain.p, no executable is created, because Pascal detects that it's a unit. But I want it to be an executable in addition to a library.

$ ./scriptedmain
-bash: ./scriptedmain: No such file or directory

test.p:

program Test;
uses
    ScriptedMain;
begin
    write('Test: The meaning of life is: ');
    writeln(MeaningOfLife())
end.

When I compile test.p with fpc test.p, the resulting executable combines the two begin/end declarations (NOT the desired behavior).

$ ./test 
Main: The meaning of life is: 42
Test: The meaning of life is: 42

Answer 1

I don't know what flavour of Pascal you're using but some variants support conditional compilation with {$IFC condition} ... {$ENDC}. You could perhaps use this in conjunction with a compile time define to include/exclude code that you need or don't need in a given version.

Answer 2

Thanks to Ager and Zhirov in the Free Pascal mailing list, I was able to construct a working scripted main example with minimal hacks. Also posted on RosettaCode.

Makefile:

all: scriptedmain

scriptedmain: scriptedmain.pas
    fpc -dscriptedmain scriptedmain.pas

test: test.pas scriptedmain
    fpc test.pas

clean:
    -rm test
    -rm scriptedmain
    -rm *.o
    -rm *.ppu

scriptedmain.pas:

{$IFDEF scriptedmain}
program ScriptedMain;
{$ELSE}
unit ScriptedMain;
interface
function MeaningOfLife () : integer;
implementation
{$ENDIF}
    function MeaningOfLife () : integer;
    begin
        MeaningOfLife := 42
    end;
{$IFDEF scriptedmain}
begin
    write('Main: The meaning of life is: ');
    writeln(MeaningOfLife())
{$ENDIF}
end.

test.pas:

program Test;
uses
    ScriptedMain;
begin
    write('Test: The meaning of life is: ');
    writeln(MeaningOfLife())
end.

Example:

$ make
$ ./scriptedmain 
Main: The meaning of life is: 42
$ make test
$ ./test 
Test: The meaning of life is: 42