95 lines
3.6 KiB
C#
95 lines
3.6 KiB
C#
namespace Unosquare.Swan.Abstractions
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{
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using System;
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using System.Linq;
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using System.Collections.Generic;
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using System.Linq.Expressions;
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/// <summary>
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/// Represents a generic expression parser.
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/// </summary>
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public abstract class ExpressionParser
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{
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/// <summary>
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/// Resolves the expression.
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/// </summary>
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/// <typeparam name="T">The type of expression result.</typeparam>
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/// <param name="tokens">The tokens.</param>
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/// <returns>The representation of the expression parsed.</returns>
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public virtual T ResolveExpression<T>(IEnumerable<Token> tokens)
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{
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var conversion = Expression.Convert(Parse(tokens), typeof(T));
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return Expression.Lambda<Func<T>>(conversion).Compile()();
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}
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/// <summary>
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/// Parses the specified tokens.
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/// </summary>
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/// <param name="tokens">The tokens.</param>
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/// <returns>The final expression.</returns>
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public virtual Expression Parse(IEnumerable<Token> tokens)
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{
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var expressionStack = new List<Stack<Expression>>();
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foreach (var token in tokens)
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{
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if (expressionStack.Any() == false)
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expressionStack.Add(new Stack<Expression>());
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switch (token.Type)
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{
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case TokenType.Wall:
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expressionStack.Add(new Stack<Expression>());
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break;
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case TokenType.Number:
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expressionStack.Last().Push(Expression.Constant(Convert.ToDecimal(token.Value)));
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break;
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case TokenType.Variable:
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ResolveVariable(token.Value, expressionStack.Last());
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break;
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case TokenType.String:
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expressionStack.Last().Push(Expression.Constant(token.Value));
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break;
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case TokenType.Operator:
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ResolveOperator(token.Value, expressionStack.Last());
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break;
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case TokenType.Function:
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ResolveFunction(token.Value, expressionStack.Last());
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if (expressionStack.Count > 1 && expressionStack.Last().Count == 1)
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{
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var lastValue = expressionStack.Last().Pop();
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expressionStack.Remove(expressionStack.Last());
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expressionStack.Last().Push(lastValue);
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}
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break;
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}
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}
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return expressionStack.Last().Pop();
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}
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/// <summary>
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/// Resolves the variable.
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/// </summary>
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/// <param name="value">The value.</param>
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/// <param name="expressionStack">The expression stack.</param>
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public abstract void ResolveVariable(string value, Stack<Expression> expressionStack);
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/// <summary>
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/// Resolves the operator.
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/// </summary>
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/// <param name="value">The value.</param>
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/// <param name="expressionStack">The expression stack.</param>
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public abstract void ResolveOperator(string value, Stack<Expression> expressionStack);
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/// <summary>
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/// Resolves the function.
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/// </summary>
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/// <param name="value">The value.</param>
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/// <param name="expressionStack">The expression stack.</param>
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public abstract void ResolveFunction(string value, Stack<Expression> expressionStack);
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}
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}
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