Refactor: Reviewed parsing process for SpacialValueWord (e.g., true, …

…false, null)

The parsing process for special values like true, false, and null has been reviewed. This improvement ensures that these special values are interpreted correctly, distinguishing them clearly from other values and enabling more accurate parsing.

src/Carbunql.LexicalAnalyzer/Lexer.Expression.cs

@@ -74,7 +74,6 @@ public static IEnumerable<Lex> ReadExpressionLexes(ReadOnlyMemory<char> memory,
                     continue;
                 }
 
-
                 // alias, expression separator, or 'from' keyword
                 break;
             }

src/Carbunql.LexicalAnalyzer/Lexer.Value.CharactorValue.cs

@@ -1,22 +1,30 @@
-using System.Collections.Generic;
-using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Carbunql.LexicalAnalyzer;
 
 public static partial class Lexer
 {
-    /// <summary>
-    /// Defines a set of characters considered as symbols that terminate an identifier.
-    /// </summary>
-    //internal static readonly HashSet<char> Symbols = new HashSet<char>
-    //{
-    //    '+', '-', '*', '/', '%', // Arithmetic operators
-    //    '(', ')', '[', ']', '{', '}', // Brackets and braces
-    //    '~', '@', '#', '$', '^', '&', // Special symbols
-    //    '!', '?', ':', ';', ',', '.', '<', '>', '=', '|', '\\', // Other symbols
-    //    '`', '"', '\'' // Quotation marks
-    //};
-
+    private static HashSet<string> SpecialValueWords = new HashSet<string>
+    {
+        "true",
+        "false",
+        "null",
+
+        "current_timestamp",
+        "current_date",
+        "current_time",
+        "timestamp",
+        "now",
+
+        "yesterday",
+        "today",
+        "tomorrow",
+
+        "-infinity",
+        "infinity",
+        "allballs",
+        "epoch",
+    };
 
     [MemberNotNullWhen(true)]
     public static bool TryParseCharactorValue(ReadOnlyMemory<char> memory, int start, out Lex lex, out int endPosition)
@@ -41,9 +49,9 @@ public static bool TryParseCharactorValue(ReadOnlyMemory<char> memory, int start
         // Special word (e.g. true, false, null, timestamp)
         foreach (var keyword in SpecialValueWords.Where(x => x.Length == length))
         {
-            if (memory.EqualsWordIgnoreCase(position, keyword, out position))
+            if (memory.EqualsWordIgnoreCase(start, keyword, out _))
             {
-                lex = new Lex(memory, LexType.Type, start, position - start);
+                lex = new Lex(memory, LexType.Value, start, position - start);
                 endPosition = position;
                 return true;
             }
@@ -83,89 +91,6 @@ public static bool TryParseCharactorValue(ReadOnlyMemory<char> memory, int start
         return true;
     }
 
-
-    [MemberNotNullWhen(true)]
-    private static bool TryParseCharactorValues(ReadOnlyMemory<char> memory, int position, out IEnumerable<Lex> lexes)
-    {
-        lexes = Enumerable.Empty<Lex>();
-        var start = position;
-
-        if (TryGetCharacterEndPosition(memory, position, out _))
-        {
-            lexes = ParseCharactorValues(memory, position);
-            return true;
-        }
-        return false;
-    }
-
-    [MemberNotNullWhen(true)]
-    private static IEnumerable<Lex> ParseCharactorValues(ReadOnlyMemory<char> memory, int position)
-    {
-        var start = position;
-
-        if (!TryGetCharacterEndPosition(memory, position, out position))
-        {
-            throw new FormatException();
-        }
-
-        // check next charactor
-        if (memory.IsAtEndOrWhiteSpace(position))
-        {
-            if (IsSpacialValueWord(memory, start, position - start))
-            {
-                yield return new Lex(memory, LexType.Value, start, position - start);
-            }
-
-            yield return new Lex(memory, LexType.Column, start, position - start);
-            yield break;
-        }
-
-        // Identifier separator
-        if (memory.EqualsChar(position, '.', out _))
-        {
-            yield return new Lex(memory, LexType.Namespace, start, position - start);
-
-            position++;//skip comma
-            start = position;
-            while (TryGetCharacterEndPosition(memory, position, out position))
-            {
-                if (memory.EqualsChar(position, '.', out _))
-                {
-                    yield return new Lex(memory, LexType.Namespace, start, position - start);
-                    position++;//skip comma
-                    start = position;
-                    continue;
-                }
-                else
-                {
-                    yield return new Lex(memory, LexType.Column, start, position - start);
-                    yield break;
-                }
-            }
-            throw new FormatException();
-        }
-
-        // left paren
-        if (memory.EqualsChar(position, '(', out _))
-        {
-            yield return new Lex(memory, LexType.Function, start, position - start);
-            yield break;
-        }
-
-        // mulitiword
-
-
-        // other
-        if (IsSpacialValueWord(memory, start, position - start))
-        {
-            yield return new Lex(memory, LexType.Value, start, position - start);
-            yield break;
-        }
-
-        yield return new Lex(memory, LexType.Column, start, position - start);
-        yield break;
-    }
-
     /// <summary>
     /// Attempts to find the end position of a valid identifier starting at a given position in the specified memory segment.
     /// </summary>