How to structure huge conditional statement?

Question

I'm creating some kind of a "personal assistant" application which is basically a web service that receives a message and then does something according to it.

For example I send "what time is it?" and I get the current time as answer. Other examples:

"tell me a joke" -> queries and sends some joke from an public api
"I have to [X] -> sets [X] to todo list
"What do I have to do?" -> sends todo list
"Start my pc" -> Starts PC via Wake On Lan

or what ever else comes to my mind.

My first prototype just uses an if else statment which looks something like

if message.contains("foo"):
  # do foo stuff
elif message.contains("bar"):
  # do bar stuff

Of course this will be a total mess after adding several commands so I'm thinking about what would be a good concept to structure such a huge conditional statement.

(I'm using Python with the web.py framework)

One idea is to use some list / map to create a mapping between key words and associated functions and split functionality in different classes (like a todo list module and so on).

There are applications like WolframAlpha or Siri which have just a single input method but several hundred or thousand different functions in the brackground. Of course those are on a totally different level but in general, how do you create a nice and clean branching from a single input to a big number of different functions?

Robert Harvey · Answer 1 · 2016-03-02T16:14:10.773

The usual approach to mapping strings to functions is to use a dictionary or hashtable. Here is what it would look like in C#:

var commands = new Dictionary<string, Action<string>>();

This creates a hash table with a string key and a method delegate taking one parameter (in this case a string. You can use the parameter however you want).

You can create the commands at compile time:

var commands = new Dictionary<string, Action<string>>
{
    { "Tell me a joke", TellJoke }, 
    { "I have to",  IHaveTo }
};

or at runtime:

commands.add("Tell me a joke", TellJoke);

Where TellJoke is some method that takes one parameter and returns nothing. After a bit of pre-processing of the search string, the mapped function would then be called thusly:

Commands[searchKey](searchString);

or more robustly:

bool ExecuteCommand(string key, string search)
{
    if (commands.Contains(key))
    {
        Commands[searchKey](search);
        return true;
    }
    return false;
}

Of course, a real personal assistant wouldn't work this way. You would have some sort of engine that can be modified at runtime, not compile time, so that it can learn.

How to structure huge conditional statement?

1 Answers1