prep(1)

There are tons of pre-processors for Fortran. What are the pros and cons of prep(1) over others?

Sustainable

prep(1) is written in Fortran, making it very easily maintained or modified in a Fortran programming environment. The file standalone/prep.f90 is a single Fortran file that intentionally avoids platform-specific code.

Basic Templating

prep(1) allows for templating via variable expansion using a POSIX-shell syntax which many are familiar with

Fortran-like syntax

Conditional expressions may be written very close to Fortran syntax, allowing for a low learning curve for Fortran programmers.

Text-based documentation can easily be maintained in the source file

It allows for plain text blocks to be written to a file, allowing markdown, HTML, and Latex to be easily incorporated straight in the code file, including an option to literally keep code in a Markdown file with the code delimited between the lines "```fortran" and "```".

The plain text blocks can additionally be filtered to become a CHARACTER array definition, WRITE() statements or comments.

It is a lot easier to maintain a large amount of text as simple lines than to maintain them as properly formatted variable definitions, for example.

A command-line flag (preliminary) allows the same text block to be formatted for use with Ford or Doxygen or as as-is comments. Support of in-line documentation is not a common Fortran-compatible preprocessor feature.

No collisions with cpp(1)

prep(1) intentionally does not use a pound prefix by default so that files (especially C) that already contain cpp(1) directives can be mixed in without collisions.

Easy access to environment variables

prep(1) also allows environment variables to be imported, and by default $IFNDEF|$IFDEF will test for environment variables as well as variables declared with $DEFINE. This allows for easier communication with the programming environment than fpp(1) or cpp(1) which require that kind of information to be passed in on the command line.

On the con side ...

prep(1) allows reuse of blocks but not true looping or a “for” statement.

cpp(1) and fpp(1) are often tightly coupled with the compiler, allowing for compiler-specific pre-defined variables. Supporting importing of environment variables addresses this to some extent.

Currently, prep(1) does not insert "# NNN “filename” lines for the debugger, but line counts and input files are tracked so that would be trivial to add.

There is not a warning about line length being exceeded nor support for automatic continuation lines. Again, easy to add but there should at least be a warning, as the changes to Fortran to eliminate the 132 column default line length limit will not be available on all compilers for a while although a lot of compilers already allow that.

Crib Sheet

EXPRESSIONS
  numeric operators are +,-,*,/,**, (). Logical operators are
   >  | .EQ.| .NE.| .GE.| .GT.| .LE.| .LT.|.NOT.|.AND.| .OR.| .EQV.|.NEQV.|
   >  |  == |  /= |  >= |  >  |  <= |  <  |  !  |  && |  || |  ==  |  !=  |
  $DEFINE variable_name[=expression][;...]
   > Predefined values are "OS", which is set to a guess of the system type, and
   > UNKNOWN=0 LINUX=1 MACOS=2 WINDOWS=3 CYGWIN=4 SOLARIS=5 FREEBSD=6 OPENBSD=7.
   > SYSTEMON is .TRUE. if --system is present on the command line, else .FALSE.
  $UNDEFINE|$UNDEF variable_name[;...]
CONDITIONAL CODE SELECTION:
  $IF logical_integer-based_expression| [.NOT.] DEFINED(varname[,...])
  $IFDEF|$IFNDEF variable_or_envname
  $ELSEIF|$ELIF logical_integer-based_expression
  $ELSE
  $ENDIF
MACRO STRING EXPANSION AND TEXT REPLAY:
   > Unless at least one variable name is defined no ${NAME} expansion occurs.
  $SET varname string
  $$UNSET variable_name[;...]
  $IMPORT envname[;...]
   > $set author  William Shakespeare
   > $import HOME
   > write(*,*)'${AUTHOR} ${DATE} ${TIME} File ${FILE} Line ${LINE} HOME ${HOME}
  $PARCEL blockname ... $ENDPARCEL ! a reuseable parcel of expandable text
  $POST   blockname(s)  ! insert a defined parcel of text
EXTERNAL FILES (see $BLOCK ... --file also)
  $OUTPUT filename [--append]
  $INCLUDE filename
TEXT BLOCK FILTERS (--file writes to $PREP_DOCUMENT_DIR/doc/NAME)
  $BLOCK [comment|null|write|variable [--varname NAME]|set|system|message|
         define|help|version][--file NAME [--append]] ... $ENDBLOCK
INFORMATION
  $MESSAGE message_to_stderr
  $SHOW [defined_variable_name][;...]
SYSTEM COMMANDS (see also: $BLOCK SYSTEM)
  $SYSTEM command
  $STOP [stop_value[ "message"]] | $QUIT ["message"]| $ERROR ["message"]