fortranFunctionParser.f90

program main

    use function_parser
    use iso_fortran_env, only: wp => real64, output_unit

    implicit none
    character(len=50):: func ='sin(x)'
    integer,parameter :: nvar = 1  !! number of variables
    character(len=*),dimension(nvar),parameter :: var  = [ 'x' ]
    real(wp),dimension(nvar) :: val  = [  2.0_wp  ]

    type(fparser) :: parser
    real(wp) :: res
    real(wp) :: x
    real:: A

    write(*,*) 'Please enter your function f(x):'
    read(*,*) func
    write(*,*) 'Please enter value for x:'
    read(*,*) A
    val = [A]
    call parser%parse(func, var, .false.)  ! parse and bytecompile function string
    if (parser%error()) then
        call parser%print_errors(output_unit)
    else
        call parser%evaluate(val,res)  ! interprete bytecode representation of function
        if (parser%error()) then
            call parser%print_errors(output_unit)
        else
            write(*,*) 'f(x)=',func
            write(*,'(/X,A2,F5.2,A2,F15.8/)') 'f(',A,')=',res
        end if
    end if
end