Add formula engine: data-driven expression evaluator (Core)
CI / build-test (push) Successful in 1m19s
CI / build-test (push) Successful in 1m19s
Keystone for the gene system. A Formula compiles a string from a def (lexer -> recursive-descent parser -> tree of Func<IFormulaContext,float>) once, then evaluates allocation-free against a variable context. Supports + - * / %, comparisons, && || !, ternary, the constants pi/tau/e, and functions abs sign floor ceil round sqrt exp log sin cos tan min max pow clamp lerp step. Deterministic and side-effect-free so gene-effect formulas stay pure. Covered by FormulaTests (parsing, precedence, functions, logic/ternary, variables, errors). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Leonid Pershin
co-authored by
Claude Opus 4.8
Claude Opus 4.8
parent
2ac074004a
commit
10898b08a0
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using System.Globalization;
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namespace MrGameEng.Formulas;
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internal enum TokenType
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{
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Number,
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Identifier,
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Plus,
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Minus,
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Star,
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Slash,
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Percent,
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LParen,
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RParen,
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Comma,
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Less,
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Greater,
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LessEqual,
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GreaterEqual,
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EqualEqual,
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NotEqual,
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And,
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Or,
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Not,
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Question,
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Colon,
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End,
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}
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internal readonly struct Token(TokenType type, int position, float number = 0f, string text = "")
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{
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public TokenType Type { get; } = type;
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public int Position { get; } = position;
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public float Number { get; } = number;
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public string Text { get; } = text;
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}
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/// <summary>
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/// Turns a formula string into a flat token list. Pure and allocation-light; recognizes numbers,
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/// identifiers, the arithmetic/comparison/logical operators and the punctuation the parser needs.
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/// </summary>
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internal static class FormulaLexer
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{
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public static List<Token> Tokenize(string source)
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{
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var tokens = new List<Token>();
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var i = 0;
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while (i < source.Length)
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{
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var c = source[i];
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if (char.IsWhiteSpace(c))
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{
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i++;
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continue;
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}
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if (
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char.IsDigit(c)
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|| (c == '.' && i + 1 < source.Length && char.IsDigit(source[i + 1]))
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)
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{
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var start = i;
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while (i < source.Length && (char.IsDigit(source[i]) || source[i] == '.'))
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{
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i++;
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}
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var span = source.AsSpan(start, i - start);
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if (
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!float.TryParse(
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span,
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NumberStyles.Float,
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CultureInfo.InvariantCulture,
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out var value
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)
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)
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{
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throw new FormulaException(
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$"Invalid number '{span.ToString()}' at position {start}."
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);
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}
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tokens.Add(new Token(TokenType.Number, start, value));
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continue;
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}
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if (char.IsLetter(c) || c == '_')
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{
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var start = i;
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while (i < source.Length && (char.IsLetterOrDigit(source[i]) || source[i] == '_'))
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{
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i++;
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}
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tokens.Add(
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new Token(TokenType.Identifier, start, text: source.Substring(start, i - start))
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);
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continue;
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}
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var pos = i;
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switch (c)
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{
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case '+':
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tokens.Add(new Token(TokenType.Plus, pos));
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i++;
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break;
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case '-':
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tokens.Add(new Token(TokenType.Minus, pos));
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i++;
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break;
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case '*':
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tokens.Add(new Token(TokenType.Star, pos));
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i++;
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break;
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case '/':
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tokens.Add(new Token(TokenType.Slash, pos));
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i++;
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break;
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case '%':
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tokens.Add(new Token(TokenType.Percent, pos));
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i++;
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break;
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case '(':
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tokens.Add(new Token(TokenType.LParen, pos));
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i++;
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break;
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case ')':
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tokens.Add(new Token(TokenType.RParen, pos));
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i++;
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break;
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case ',':
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tokens.Add(new Token(TokenType.Comma, pos));
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i++;
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break;
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case '?':
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tokens.Add(new Token(TokenType.Question, pos));
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i++;
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break;
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case ':':
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tokens.Add(new Token(TokenType.Colon, pos));
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i++;
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break;
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case '<':
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i = AddMaybeEqual(tokens, source, i, TokenType.LessEqual, TokenType.Less);
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break;
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case '>':
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i = AddMaybeEqual(tokens, source, i, TokenType.GreaterEqual, TokenType.Greater);
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break;
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case '=':
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if (Next(source, i) == '=')
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{
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tokens.Add(new Token(TokenType.EqualEqual, pos));
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i += 2;
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break;
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}
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throw new FormulaException($"Expected '==' at position {pos}.");
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case '!':
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if (Next(source, i) == '=')
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{
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tokens.Add(new Token(TokenType.NotEqual, pos));
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i += 2;
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break;
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}
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tokens.Add(new Token(TokenType.Not, pos));
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i++;
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break;
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case '&':
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if (Next(source, i) == '&')
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{
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tokens.Add(new Token(TokenType.And, pos));
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i += 2;
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break;
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}
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throw new FormulaException($"Expected '&&' at position {pos}.");
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case '|':
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if (Next(source, i) == '|')
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{
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tokens.Add(new Token(TokenType.Or, pos));
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i += 2;
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break;
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}
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throw new FormulaException($"Expected '||' at position {pos}.");
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default:
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throw new FormulaException($"Unexpected character '{c}' at position {pos}.");
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}
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}
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tokens.Add(new Token(TokenType.End, source.Length));
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return tokens;
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}
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private static int AddMaybeEqual(
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List<Token> tokens,
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string source,
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int i,
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TokenType withEqual,
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TokenType plain
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)
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{
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if (Next(source, i) == '=')
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{
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tokens.Add(new Token(withEqual, i));
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return i + 2;
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}
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tokens.Add(new Token(plain, i));
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return i + 1;
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}
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private static char Next(string source, int i) => i + 1 < source.Length ? source[i + 1] : '\0';
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}
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