Compiling program code files (.4gl)

The .4gl source files must be compiled to .42m p-code files, in order to be loaded by the runtime system.

Understanding .4gl source compilation

Genero BDL source code modules (with .4gl file extension) must be compiled to p-code modules (with .42m file extension) by using the fglcomp tool.

Compiled p-code modules are independent of the platform and processor architecture. They are interpreted by the Genero runtime system (fglrun).

The following lines show the compilation of the prog.4gl source, in a UNIX™ shell session:

$ cat prog.4gl
MAIN
  DISPLAY "hello"
END MAIN

$ fglcomp prog.4gl

$ ls -s prog.42m
   4 prog.42m

Output directory for .42m pcode files

By default, fglcomp creates the .42m files in the current working directory, for the source files specified in the command line, and for the modules imported with IMPORT FGL module-name, when these are located in the current working directory.

When importing modules via packages, the .42m files of the modules that belong to a package are by default created in the directory of the .4gl source files. This is mandatory since the same modules names can be reused in different packages.

The output directory for .42m files can be specified with the --output-dir option of fglcomp. If the directory does not exist, it will be automatically created.

When using packages, the output directory specified with the --output-dir option defines the top-dir to create a tree of sub-directories containing the .42m files of modules imported via packages. This structure can directly be used as runtime distribution directory tree, since modules imported via packages are found automatically by fglrun, from the package-path reflecting the directory path. The FGLLDPATH environment variable can be used to specify the top-dir.

Automatic compilation of imported modules

When compiling a .4gl module that imports other modules with the IMPORT FGL instruction, if the .4gl source is more recent as the .42m file or the .42m file does not exist, fglcomp will automatically compile the imported modules, if they are located in the same directory as the compiled module, or when the module is imported via a package and located in a different directory.

For more details about auto-compilation of imported modules, see Auto-compilation of imported modules.

Verbose compilation

Consider using the --verbose option of the compiler to get detailed information about the source compilation:
$ fglcomp --verbose main.4gl
[parsing main.4gl]
[parsing mod1.4gl]
[parsing mod2.4gl]
[building mod2]
[writing mod2.42m]
[building mod1]
[writing mod1.42m]
[building main]
[writing main.42m]
...

Compiling several .4gl sources in a single command

Several .4gl source files can be provided to fglcomp: The compiler builds a dependency tree of imported modules, and compiles the files in the calculated order.
Note: When compiling multiple .4gl source files with a single fglcomp command, the process stops, if an error occurs during the compilation of a source file.

For example (assuming no .42m file exists before executing this command), if the main.4gl module imports module1.4gl, but does not import module2.4gl, when passing main.4gl module1.4gl module2.4gl as arguments to fglcomp, the compiler will first compile the module2.4gl because it is independent. Then module1.4gl is compiled,because it is imported by main.4gl, and finaly main.4gl:

$ rm *.42m
$ fglcomp --verbose main.4gl module1.4gl module2.4gl
[parsing module2.4gl]
[building module2]
[writing module2.42m]
[parsing module1.4gl]
[building module1]
[writing module1.42m]
[parsing main.4gl]
[building main]
[writing main.42m]
...
The fglcomp and fglform compilers support MATCHES-style pattern on the command line, to achieve pathname expansion:
fglcomp [a-z]*.4gl
This feature exists on any supported platform, including Microsoft™ Windows®.
Note: On UNIX plarforms, pathname expansion is part of the shell interpreter. File names are resolved before Genero commands get the specified argument(s). In order to use the Genero build-in pathname expansion on a Unix platform, specify the search pattern in single quotes:
fglcomp '[a-z]*.4gl'
For more details about supported patterns and wildcards, see the os.Path.glob utility method.
Use the --keep-going option, to continue with the compilation of the remaining source files, in case one of the source files passed as argument fails to compile:
$ fglcomp -M --verbose --keep-going "module?.4gl"
[parsing module1.4gl]
[building module1]
[writing module1.42m]
[parsing module2.4gl]
module2.4gl:2:13:2:30:error:(-6609) A grammatical error has been found ...
[parsing module2 cancelled: 1 errors]
[parsing module3.4gl]
[building module3]
[writing module3.42m]
[fglcomp: *** Errors in 1 of 3 files]

Detecting unused symbols

When a source code is modified several times, it can happen that a variable definition is left even if the variable is no longer used. The same can happen for function parameters, as well as unused DECLARE and PREPARE statements and unused imported modules.

To detect such mistakes and cleanup the source, fglcomp provides the -W unused option:
$ cat p.4gl
MAIN
    DEFINE v INT
END MAIN
FUNCTION func1(p1 INT, p2 INT) RETURNS()
    DISPLAY p1
END FUNCTION

$ fglcomp -M -Wunused p.4gl
p.4gl:2:12:2:12:warning:(-6615) The symbol 'v' is unused.
p.4gl:4:24:4:25:warning:(-6615) The parameter 'p2' is unused.

The -W unused-parameter option is dedicated to the detection of unused function parameters. It can be used individually, or it can be combined to -W unused in its negative form -W no-unused-parameter, to get all unused symbols warnings, except for function parameters.

Stricter compilation options

By default, fglcomp allows you to compile legacy application sources in a relaxed manner. For example, it is possible to compile a module calling a function which is not defined in that module, and resolved during the link process.

In recent developments based on features such as IMPORT FGL, consider using fglcomp options that make the compilation stricter:
  • --resolve-calls: To check that all functions used by a module are defined locally, or by imported modules.
  • -W all: To print all type of warnings.
  • -W error: To stop compilation if a warning occurs.
  • -M: To write error messages to standard output instead of producing a .err file.

For more details about fglcomp options, see the fglcomp command reference topic.

Additionally, the linker provides options such as --print-imports and --print-missing-imports, that produce useful information to use new language features.

Compiling in make mode

The fglcomp compiler supports the --make option, to compile all provided sources, in the way the make utility does: If the .42m file is older than the .4gl file, it will be recompiled. If the .42m is up-to-date with the .4gl, it is not recompiled.

As with a regular compilation (not using the --make option), for a provided .4gl module, imported modules will be automatically compiled when needed.

To test the compilation process and dependencies without actually compiling the modules, add the --simulate option, to see what modules would be compiled. The --simulate option can also be used without the --make option: fglcomp will then print the modules that would be compiled, even if the .42m file is up to date.

Tip: fglcomp produces the .42m files in the current working directory. Consider creating a bin directory, to hold all .42m files, and run the compiler in this directory by providing relative paths of the .4gl sources. It is also possible to use the --output-dir option.

For example:

$ tree .
.
|-- bin
|-- dir1
|   |-- module1.4gl
|   |-- module2.4gl
|   `-- module3.4gl
|-- prog1.4gl
`-- prog2.4gl

2 directories, 5 files

$ head *.4gl */*.4gl
==> prog1.4gl <==
IMPORT FGL module1
MAIN
    CALL module1.function1()
END MAIN

==> prog2.4gl <==
IMPORT FGL module2
MAIN
    CALL module2.function2()
END MAIN

==> dir1/module1.4gl <==
FUNCTION function1()
END FUNCTION

==> dir1/module2.4gl <==
IMPORT FGL module3
FUNCTION function2()
    CALL module3.function3()
END FUNCTION

==> dir1/module3.4gl <==
FUNCTION function3()
END FUNCTION
Go to the bin directory:
$ cd bin
Assuming there are no .42m in this directory tree, first check what would be compiled if we pass all .4gl sources to fglcomp:
$ fglcomp --make --simulate ../*.4gl ../*/*.4gl
[fglcomp ../dir1/module1.4gl]
[fglcomp ../prog1.4gl]
[fglcomp ../dir1/module3.4gl]
[fglcomp ../dir1/module2.4gl]
[fglcomp ../prog2.4gl]
Now compile (same output as simulated previously): fglcomp produces the .42m files:
$ fglcomp --make *.4gl dir1/*.4gl
[fglcomp ../dir1/module1.4gl]
[fglcomp ../prog1.4gl]
[fglcomp ../dir1/module3.4gl]
[fglcomp ../dir1/module2.4gl]
[fglcomp ../prog2.4gl]

$ ls 
module1.42m  module2.42m  module3.42m  prog1.42m  prog2.42m
Touch some modules and see which one are recompiled, based on the IMPORT FGL dependence tree:
$ sleep 1 && touch ../dir1/module3.4gl ../prog1.4gl
$ fglcomp --make ../*.4gl ../*/*.4gl
[fglcomp ../prog1.4gl]
[fglcomp ../dir1/module3.4gl]
[fglcomp ../dir1/module2.4gl]
[fglcomp ../prog2.4gl]

Producing make-style dependency rules

The fglcomp --dependencies option can be used to produce makefile-style dependency rules for imported modules. In the next example, the main.4gl source imports module1 and thus the main.42m compilation depends from module1.42m:
$ head *.4gl
==> main.4gl <==
IMPORT FGL module1

MAIN
    CALL module1.function1()
END MAIN

==> module1.4gl <==
FUNCTION function1()
END FUNCTION

$ fglcomp --dependencies main.4gl
main.42m: main.4gl module1.42m
	$(FGLCOMP) $<
module1.42m: module1.4gl
	$(FGLCOMP) $<

When a module is importing a non-existing module by mistake, it will be ignored by the dependencies generation process.

Circular imports are handled with proper dependency rules that can even be used for parallel builds (with make -j).

Tip: Try to perform the command fglcomp --dependencies *.4gl on all your sources and see the output.
The following generic makefile (requires GNU make) can be used to automatically produce a "depend" file with .42m/.4gl module dependencies, and compile your sources in an efficient way:
MODS=$(patsubst %.4gl,%.42m,$(wildcard *.4gl))
all:: depend $(MODS)
depend: 
        fglcomp --dependencies *.4gl > depend
clean:
        rm -f *.42? depend
FGLCOMP = fglcomp -M -Wall
-include depend
Note: If you copy/paste the above code, make sure to start command lines in rules by a TAB character!

Providing the source files in an arguments file

The fglcomp compiler supports the @argfile argument, to provide a file that contains the list of source files to be compiled. This can be used when it is not possible to pass all source files in the command line.

Only source files and patterns must be specified in the arguments file. Compiler options must be provided in the command line.

The argument file must contain one source file per line:

$ cat mysources.txt
module1.4gl
module2.4gl
module3.4gl
$ fglcomp -M -W all @mysources.txt
Note that the arguments file can contain expansion patterns as in the fglcomp command line:
$ cat mysources.txt
module[123]*.4gl
$ fglcomp -M -W all @mysources.txt

Multiple @argfile files can be provided, and mixed with filenames and patterns in the command line. The fglcomp compiler will build a list of sources to be compiled.

Handling fglcomp compiler errors

If an error occurs, the compiler writes an error file by default with the .err extension.

$ cat prog.4gl
MAIN
  LET x = "hello"
END MAIN

$ fglcomp prog.4gl
Compilation was not successful. Errors found: 1.
 The file prog.4gl has been written.

$ cat prog.err
MAIN
  LET x = "hello"
| The symbol 'x' does not represent a defined variable.
| See error number -4369. 
END MAIN

With the -M option, you can force the compiler to display an error message instead of generating an .err error file:

$ fglcomp prog.4gl
xx.4gl:2:8 error:(-4369) The symbol 'x' does not represent a defined variable.

Produce compiler warnings with -W

To improve code quality, enable compiler warnings with the -W option:

$ cat prog.4gl
MAIN
  DATABASE test1
  SELECT COUNT(*) FROM x, OUTER(y) WHERE x.k = y.k
END MAIN

$ fglcomp -W stdsql prog.4gl
xx.4gl:3: warning: SQL statement or language instruction with specific SQL syntax.

When a warning is raised, you can use the -W error option to force the compiler to stop as if an error was found.

Some warnings are generated by default (without using the -W option), when the source code uses a feature that is considered as "fragile" yet to be supported for backward compatibility.

By default warnings go to the stderr stream. When creating a .err file, warnings can be redirected to the .err file with the -W to-err-file option.

For the complete list of warning options, see -W option in fglcomp command reference.