Example #1
0
        /// <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;
        }