F is designed to be a minimal subset of Fortran, with only about one hundred intrinsic procedures. Language keywords and intrinsic function names are reserved keywords in F and no other names may take this exact form. F contains the same character set used in Fortran 90/95 with a limit of 132 characters. Reserved words are always written in lowercase. Any uppercase letter may appear in a character constant. Variable names do not have restriction and can include upper and lowercase characters.
Operators
F supports many of the standard operators used in Fortran. The operators supported by F are:
The assignment operator is denoted by the equal sign=. In addition, pointer assignment is denoted by =>. Comments are denoted by the ! symbol: variable = expression ! assignment pointer => target ! pointer assignment
Data types
Similar to Fortran, the type specification is made up of a type, a list of attributes for the declared variables, and the variable list. F provides all the same types as Fortran as well, with the sole exception of doubles: ! type :: entity declaration list real :: x, y ! declaring variables of type real x,y without an attribute list integer, dimension :: x ! declaring variable of type big integer array with the identifier x character :: student_name ! declaring a character type variable with len 100
F does not have intrinsic support for object-oriented programming, but it does allow for records: type, public :: City character :: name character :: state end type City
Variable declarations are followed by an attribute list. The attributes allowed are parameter, public, private, allocatable, dimension, intent, optional, pointer, save and target. The attribute list is followed by ::, which is part of the syntax. F also allows for optional initialization in the list of objects. All items in a list will have the same attributes in a given type declaration statement. In addition, declarations are attribute oriented instead of entity oriented.
F supports 3 statements for control flow: if, a basic conditional, case, a switch statement, and do, a conditional while loop. The return, stop, cycle, and exit statements from Fortran may be used to break control flow. real :: x do i = 100 x += i print i cycle end do max : do if then exit max: end if x = y; end max stop if then x = x + y; else if then x = y - x; end if select case : case x = 0 case x = 1 case x = 5 case default x = 10 end select
F places a heavy emphasis on modular programming. Modules in F are called "programs": program main ! Insert code here end program main
Placing procedures outside of a module is prohibited. F supports most of the modules and subroutines found in the Fortran 95standard library. All procedures in F are external by default, and require a result clause that returns the value of a function. F supports recursion. All of the intrinsic procedures found in Fortran 95 may be used in F, with the exceptions of achar, iachar, lge, lgt, lle, llt, transfer, dble, dim, dprod, and mod.
