Line Filters in Modelica

Our line filter program reads input from stdin, processes it, and then prints a derived result to stdout. In this case, it writes a capitalized version of all input text. You can use this pattern to write your own Modelica line filters.

model LineFilter
  import Modelica.Utilities.Streams;
  import Modelica.Utilities.Strings;
  
  function capitalize
    input String str;
    output String result;
  algorithm
    result := Strings.uppercase(str);
  end capitalize;

equation
  when initial() then
    while true loop
      String line;
      (line, _) := Streams.readLine("stdin");
      if line == "" then
        break;
      end if;
      Streams.print(capitalize(line));
    end while;
  end when;
end LineFilter;

In this Modelica implementation:

1. We import necessary utilities for stream operations and string manipulation.

2. We define a capitalize function that converts a string to uppercase.

3. In the equation section, we use an initial event to start the processing loop.

4. We read lines from stdin using Streams.readLine().

5. Each line is capitalized using our capitalize function.

6. The capitalized line is then printed to stdout using Streams.print().

7. We continue this process until an empty line is encountered, which signals the end of input.

To try out our line filter, first make a file with a few lowercase lines.

$ echo 'hello'   > /tmp/lines
$ echo 'filter' >> /tmp/lines

Then use the line filter to get uppercase lines. Note that the exact command to run a Modelica script may vary depending on your Modelica environment:

$ cat /tmp/lines | modelica LineFilter.mo
HELLO
FILTER

This example demonstrates how to create a simple line filter in Modelica that reads from standard input, processes the data, and writes to standard output. While Modelica is primarily used for modeling and simulation of complex systems, this example shows how it can also be used for text processing tasks.