ExpressionParser.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "Containers/Array.h"
#include "CoreTypes.h"
#include "HAL/PlatformCrt.h"
#include "Misc/ExpressionParserTypes.h"
#include "Templates/ValueOrError.h"
 
/** An expression parser, responsible for lexing, compiling, and evaluating expressions.
 *  The parser supports 3 functions:
 *      1. Lexing the expression into a set of user defined tokens,
 *      2. Compiling the tokenized expression to an efficient reverse-polish execution order,
 *      3. Evaluating the compiled tokens
 *
 *  See ExpressionParserExamples.cpp for example usage.
 */
 
namespace ExpressionParser
{
    typedef TValueOrError< TArray<FExpressionToken>, FExpressionError > LexResultType;
    typedef TValueOrError< TArray<FCompiledToken>, FExpressionError > CompileResultType;
 
    /** Lex the specified string, using the specified grammar */
    LexResultType Lex(const TCHAR* InExpression, const FTokenDefinitions& TokenDefinitions);
 
    /** Compile the specified expression into an array of Reverse-Polish order nodes for evaluation, according to our grammar definition */
    CompileResultType Compile(const TCHAR* InExpression, const FTokenDefinitions& TokenDefinitions, const FExpressionGrammar& InGrammar);
 
    /** Compile the specified tokens into an array of Reverse-Polish order nodes for evaluation, according to our grammar definition */
    CompileResultType Compile(TArray<FExpressionToken> InTokens, const FExpressionGrammar& InGrammar);
 
    /** Evaluate the specified expression using the specified token definitions, grammar definition, and evaluation environment */
    FExpressionResult Evaluate(const TCHAR* InExpression, const FTokenDefinitions& InTokenDefinitions, const FExpressionGrammar& InGrammar, const IOperatorEvaluationEnvironment& InEnvironment);
 
    /** Evaluate the specified pre-compiled tokens using an evaluation environment */
    FExpressionResult Evaluate(const TArray<FCompiledToken>& CompiledTokens, const IOperatorEvaluationEnvironment& InEnvironment);
 
    /** Templated versions of evaluation functions used when passing a specific jump table and context */
    template<typename ContextType>
    FExpressionResult Evaluate(const TCHAR* InExpression, const FTokenDefinitions& InTokenDefinitions, const FExpressionGrammar& InGrammar, const TOperatorJumpTable<ContextType>& InJumpTable, const ContextType* InContext = nullptr)
    {
        TOperatorEvaluationEnvironment<ContextType> Env(InJumpTable, InContext);
        return Evaluate(InExpression, InTokenDefinitions, InGrammar, Env);
    }
 
    template<typename ContextType>
    FExpressionResult Evaluate(const TArray<FCompiledToken>& CompiledTokens, const TOperatorJumpTable<ContextType>& InJumpTable, const ContextType* InContext = nullptr)
    {
        TOperatorEvaluationEnvironment<ContextType> Env(InJumpTable, InContext);
        return Evaluate(CompiledTokens, Env);
    }
}