/// <summary>
/// Parses a given expression into a graph.
/// </summary>
/// <returns>The built graph.</returns>
/// <param name="expression">The expression to create the graph from.</param>
/// <param name="initGraph">The graph to append too. Used for recursion.</param>
public Graph ParseExpression(string expression, Graph initGraph = null)
{
var lang = new Language ();
var ops = new Operations ();
expression = expression.Trim ();
var opStack = new Stack<Word>();
foreach (char letter in expression) {
//find the language mapping
var inLanguage = lang
.DefaultIfEmpty(null)
.FirstOrDefault (w => w.Letter == letter);
//find the operation mapping
var inOps = ops
.DefaultIfEmpty(null)
.FirstOrDefault(w => w.Letter == letter);
//not in the language or operators
if(inLanguage == null && inOps == null){
throw new InvalidLanguageException("Invalid input: " + letter);
}
//it is valid language input, so add it to the list.
if(inLanguage != null){
opStack.Push(inLanguage);
continue;
}
else{
//not a letter, so must be an operation
//verify that it has the correct arg count for that type of operation.
if (opStack.Count != inOps.MinArgCount && initGraph == null) {
throw new InvalidLanguageException (
string.Format(
"Unbalanced arguement count for operation (expected {0}, but got {1}.",
inOps.MinArgCount, opStack.Count
));
}
//operation, so stop, and process graph
initGraph = ProcessOperation(initGraph, inOps, opStack);
}
}
//expression was given with no operation, so error out.
if (opStack.Count > 0) {
throw new InvalidLanguageException ("No operation was specified in the given expression.");
}
//once done with graph, renumber the states.
initGraph.RenumberStates ();
//return the completed graph.
return initGraph;
}