How to resolve the algorithm S-expressions step by step in the C# programming language

Problem Statement
Step by Step Solution
Sourcecode

Problem Statement

S-Expressions are one convenient way to parse and store data.

Write a simple reader and writer for S-Expressions that handles quoted and unquoted strings, integers and floats. The reader should read a single but nested S-Expression from a string and store it in a suitable datastructure (list, array, etc). Newlines and other whitespace may be ignored unless contained within a quoted string. “()” inside quoted strings are not interpreted, but treated as part of the string. Handling escaped quotes inside a string is optional; thus “(foo"bar)” maybe treated as a string “foo"bar”, or as an error. For this, the reader need not recognize “\” for escaping, but should, in addition, recognize numbers if the language has appropriate datatypes. Languages that support it may treat unquoted strings as symbols. Note that with the exception of “()"” (“\” if escaping is supported) and whitespace there are no special characters. Anything else is allowed without quotes. The reader should be able to read the following input and turn it into a native datastructure. (see the Pike, Python and Ruby implementations for examples of native data structures.) The writer should be able to take the produced list and turn it into a new S-Expression. Strings that don't contain whitespace or parentheses () don't need to be quoted in the resulting S-Expression, but as a simplification, any string may be quoted.

Let the writer produce pretty printed output with indenting and line-breaks.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm S-expressions step by step in the C# programming language

Overview

This code defines classes and methods to manipulate and serialize S-Expressions, a data structure used in Lisp-like programming languages. It provides functionality to convert between a string representation and a tree-like hierarchical structure.

Implementation Details

1. SNode Class:

Represents a node in the S-Expression tree.
Contains a list of child nodes _items and a name Name.
Provides read-only access to the child nodes list.
Defines constructors for creating nodes with or without a name.
Includes a method AddNode to add child nodes.

2. SNodeFull Class:

Extends SNode.
Introduces an IsLeaf property to indicate if the node is a leaf node (has no children).
Adds a RootNode property for tracking the root node of the tree.
Overrides the AddNode method to set the RootNode for the added node.

3. SExpression Class:

Implements the ISExpression interface.
Defines methods for serializing and deserializing S-Expressions.

4. Serialize Methods:

Serialize(SNode root): Serializes the tree rooted at root into a string.
Serialize(SNode node, StringBuilder sb): Recursive method that appends the serialized representation of node to the StringBuilder sb.
SerializeItem(SNode node, StringBuilder sb): Serializes a leaf node node by quoting it if necessary.

5. Deserialize Methods:

Deserialize(string st): Deserializes an S-Expression string into a tree.
Deserialize(ref string st, SNodeFull root): Recursive method that constructs the tree by processing the serialized string st.
DeserializeItem(ref string st): Deserializes a single item (leaf node or subexpression) from the serialized string.

6. Test Program:

Deserializes a sample S-Expression string, serializes the resulting tree, and prints the serialized result.

Sample Usage:

// Deserialize an S-Expression
var node = se.Deserialize(str);

// Serialize the tree
var result = se.Serialize(node);

// Print the serialized result
Console.WriteLine(result);

Source code in the csharp programming language

using System;
using System.Collections.Generic;
using System.Text;

  public class SNode
    {
        private List<SNode> _items;
        public string Name { get; set; }
        public IReadOnlyCollection<SNode> Items { get { return _items.AsReadOnly(); } }
        public SNode()
        {
            this._items = new List<SNode>();
        }
        public SNode(string name):this()
        {
            this.Name=name;
        }
        public void AddNode(SNode node)
        {
            this._items.Add(node);
        }      
    }

    public class SNodeFull : SNode
    {
        private bool _isLeaf;
        public bool IsLeaf { get => _isLeaf; }
        public SNodeFull(bool isLeaf) : base()
        {
            this._isLeaf = isLeaf;
        }

        public SNodeFull(string name, bool isLeaf) : base(name)
        {
            this._isLeaf = isLeaf;
        }

        public SNodeFull RootNode { get; set; }

        public void AddNode(SNodeFull node)
        {
            base.AddNode(node);
            node.RootNode = this;
        }
    }


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SExpression
{
    public partial class SExpression
    {
        public const string ErrorStrNotValidFormat = "Not valid format.";
    }
    public partial class SExpression : ISExpression
    {
        public String Serialize(SNode root)
        {
            if (root == null)
            {
                throw new ArgumentNullException();
            }
            var sb = new StringBuilder();
            Serialize(root, sb);
            return sb.ToString();
        }
        private void Serialize(SNode node, StringBuilder sb)
        {
            sb.Append('(');

            if (node.Items.Count > 0)
            {
                int x = 0;
                foreach (var item in node.Items)
                {
                    if (x>0)
                    {
                    sb.Append(' ');
                    }
                    else
                    {
                        x++;
                    }
                    if (item.Items.Count > 0)
                    {
                        Serialize(item, sb);
                    }
                    else
                    {
                        SerializeItem(item, sb);
                    }
                }
            }

            sb.Append(')');
        }
        private void SerializeItem(SNode node, StringBuilder sb)
        {
            if (node.Name == null)
            {
                sb.Append("()");
                return;
            }
            node.Name = node.Name.Replace("\"", "\\\"");
            if (node.Name.IndexOfAny(new char[] { ' ', '"', '(', ')' }) != -1 || node.Name == string.Empty)
            {
                sb.Append('"').Append(node.Name).Append('"');
                return;
            }
            sb.Append(node.Name);
        }
    }
    public partial class SExpression
    {
        public SNode Deserialize(string st)
        {
            if (st==null)
            {
                return null;
            }
            st = st.Trim();
            if (string.IsNullOrEmpty(st))
            {
                return null;
            }

            var begin = st.IndexOf('(');
            if (begin != 0)
            {
                throw new Exception();
            }
            var end = st.LastIndexOf(')');
            if (end != st.Length - 1)
            {
                throw new Exception(ErrorStrNotValidFormat);
            }
            st = st.Remove(st.Length-1).Remove(0, 1).ToString();
            var node = new SNodeFull(false);
            Deserialize(ref st, node);
            return node;
        }

        private void Deserialize(ref string st, SNodeFull root)
        {
            st = st.Trim();
            if (string.IsNullOrEmpty(st))
            {
                return;
            }

            SNodeFull node = null;
            SNodeFull r = root;
            do
            {
                while (st[0] == ')')
                {
                    st = st.Remove(0, 1).Trim();
                    if (st.Length==0)
                    {
                        return;
                    }
                    r = root.RootNode;
                    if (r==null)
                    {
                        throw new Exception(ErrorStrNotValidFormat);
                    }
                }
                node = DeserializeItem(ref st);
                st = st.Trim();

                r.AddNode(node);
               
                if (!node.IsLeaf)
                {
                    Deserialize(ref st,node);
                }
            }
            while (st.Length > 0);
            
        }

        private SNodeFull DeserializeItem(ref string st)
        {
            if (st[0] == '(')
            {
                st = st.Remove(0, 1);
                return new SNodeFull(false);
            }

            var x = 0;
            var esc = 0;
            for (int i = 0; i < st.Length; i++)
            {
                if (st[i] == '"')
                {
                    if (esc == 0)
                    {
                        esc = 1;
                    }
                    else if(esc == 1 && (i> 0 && st[i - 1] == '\\'))
                    {
                        throw new Exception(ErrorStrNotValidFormat);
                    }
                    else
                    {
                        esc = 2;
                        break;
                    }
                }
                else if (esc==0 && " ()".Contains(st[i]))
                {
                    break;
                }

                x++;
            }
            if (esc == 1)
            {
                throw new Exception(ErrorStrNotValidFormat);
            }

            var head = esc==0? st.Substring(0, x): st.Substring(1,x-1);
            st = st.Remove(0, esc ==0 ? x: x + 2);
            return new SNodeFull(head, true);
        }
    }
}


using System;
using System.Collections.Generic;

namespace SExpression.Test
{
    class Program
    {
        static void Main(string[] args)
        {
            var str = 
@"((data ""quoted data"" 123 4.5)
(data(!@# (4.5) ""(more"" ""data)"")))";

            var se = new SExpression();
            var node = se.Deserialize(str);
            var result = se.Serialize(node);
            Console.WriteLine(result);
        }
    }
}

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