Closures in VHDL

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity Closures is
end Closures;

architecture Behavioral of Closures is
    -- Function to create a counter
    function int_seq return integer is
        variable i : integer := 0;
    begin
        i := i + 1;
        return i;
    end function;

    -- Signals to store the counter values
    signal next_int, new_ints : integer := 0;
begin
    process
    begin
        -- Call int_seq multiple times to demonstrate the closure-like behavior
        next_int <= int_seq;
        wait for 10 ns;
        next_int <= int_seq;
        wait for 10 ns;
        next_int <= int_seq;
        wait for 10 ns;

        -- Create a new instance to show independent state
        new_ints <= int_seq;
        wait for 10 ns;

        wait;
    end process;
end Behavioral;

VHDL doesn’t have direct support for closures or anonymous functions like in some high-level programming languages. However, we can simulate a similar behavior using functions and variables within an architecture.

In this example, we define a function int_seq that acts like a counter. Each time it’s called, it increments and returns a value. This simulates the closure-like behavior of maintaining state between function calls.

The process block in the architecture demonstrates the usage of this function. We call int_seq multiple times and assign its value to the next_int signal, simulating the behavior of calling a closure.

To demonstrate that each instance maintains its own state, we create another signal new_ints and assign it a new call to int_seq.

Note that in VHDL, we use signals and wait statements to simulate the passage of time and sequential execution, as VHDL is primarily used for hardware description and simulation.

To run this VHDL code, you would typically use a VHDL simulator. The simulation would show the values of next_int incrementing from 1 to 3, and new_ints starting again from 1, demonstrating the independent state of each “instance” of the function.

This example demonstrates how we can achieve behavior similar to closures in VHDL, even though the language doesn’t natively support this concept in the same way as high-level software programming languages.