Makefile and code - illegal fortran syntax?

Makefile

.PHONY: all pgi intel gcc nag clean

all: gcc intel nag pgi

pgi:
        pgfortran -V
        pgfortran -Minform=inform -Mbounds intertest.f90 -o intertest-pgi
        ./intertest-pgi

intel:
        ifort -V
        ifort -warn -check intertest.f90 -o intertest-intel
        ./intertest-intel

nag:
        nagfor -V
        nagfor intertest.f90 -o intertest-nag
        ./intertest-nag

gcc:
        gcc --version
        gfortran -Wall -Wextra -fcheck=all intertest.f90 -o intertest-gcc
        ./intertest-gcc

clean:
        rm -f *.mod intertest-pgi intertest-gcc intertest-intel

% for fc in gcc intel nag pgi; do echo "---------- Compiler: $fc" ; make $fc; done                                                                          [paul@bender.sintef.no]
---------- Compiler: gcc
gcc --version
gcc (Ubuntu 4.8.5-2ubuntu1~14.04.1) 4.8.5
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

gfortran -Wall -Wextra -fcheck=all intertest.f90 -o intertest-gcc
./intertest-gcc
 If this prints 3.14, all is OK:    3.14000010
---------- Compiler: intel
ifort -V
Intel(R) Fortran Intel(R) 64 Compiler for applications running on Intel(R) 64, Version 16.0.2.181 Build 20160204
Copyright (C) 1985-2016 Intel Corporation.  All rights reserved.

ifort -warn -check intertest.f90 -o intertest-intel
./intertest-intel
 If this prints 3.14, all is OK:    3.140000
---------- Compiler: nag
nagfor -V
NAG Fortran Compiler Release 6.0(Hibiya) Build 1057
Product NPL6A60NA for x86-64 Linux
Copyright 1990-2015 The Numerical Algorithms Group Ltd., Oxford, U.K.
nagfor intertest.f90 -o intertest-nag
NAG Fortran Compiler Release 6.0(Hibiya) Build 1057
Error: intertest.f90, line 11: Syntax error
       detected at PROCEDURE@::
[NAG Fortran Compiler pass 1 error termination, 1 error]
Makefile:16: recipe for target 'nag' failed
make: *** [nag] Error 2
---------- Compiler: pgi
pgfortran -V

pgfortran 15.7-0 32-bit target on x86-64 Linux -tp sandybridge
The Portland Group - PGI Compilers and Tools
Copyright (c) 2015, NVIDIA CORPORATION.  All rights reserved.
pgfortran -Minform=inform -Mbounds intertest.f90 -o intertest-pgi
PGF90-S-0034-Syntax error at or near :: (intertest.f90: 11)
  0 inform,   0 warnings,   1 severes, 0 fatal for intertest
Makefile:6: recipe for target 'pgi' failed
make: *** [pgi] Error 2

module intertest
    implicit none

    type beta
        real :: val
    end type beta

    interface beta
        module procedure :: beta_constructor
    end interface beta

contains

    function beta_constructor(val) result(this)
        implicit none
        type(beta) :: this
        real, intent(in) :: val

        this%val = val
    end function beta_constructor

end module intertest


program test_interface
    use intertest
    implicit none

    type(beta) :: b

    b = beta(3.14)
    print *, "If this prints 3.14, all is OK: ", b%val
end program test_interface