Merge pull request #7663 from jordan-woyak/expression-parser-improve

Expression parser improvements

Source/Core/DolphinQt/Config/Mapping/IOWindow.cpp

@@ -4,6 +4,7 @@
 
 #include "DolphinQt/Config/Mapping/IOWindow.h"
 
+#include <optional>
 #include <thread>
 
 #include <QComboBox>
@@ -11,7 +12,9 @@
 #include <QGroupBox>
 #include <QHBoxLayout>
 #include <QLabel>
+#include <QLineEdit>
 #include <QListWidget>
+#include <QMessageBox>
 #include <QPlainTextEdit>
 #include <QPushButton>
 #include <QSlider>
@@ -25,22 +28,174 @@
 #include "DolphinQt/QtUtils/BlockUserInputFilter.h"
 
 #include "InputCommon/ControlReference/ControlReference.h"
+#include "InputCommon/ControlReference/ExpressionParser.h"
 #include "InputCommon/ControllerEmu/ControllerEmu.h"
 #include "InputCommon/ControllerInterface/ControllerInterface.h"
 
 constexpr int SLIDER_TICK_COUNT = 100;
 
+namespace
+{
+// TODO: Make sure these functions return colors that will be visible in the current theme.
+QTextCharFormat GetSpecialCharFormat()
+{
+  QTextCharFormat format;
+  format.setFontWeight(QFont::Weight::Bold);
+  return format;
+}
+
+QTextCharFormat GetLiteralCharFormat()
+{
+  QTextCharFormat format;
+  format.setForeground(QBrush{Qt::darkMagenta});
+  return format;
+}
+
+QTextCharFormat GetInvalidCharFormat()
+{
+  QTextCharFormat format;
+  format.setUnderlineStyle(QTextCharFormat::WaveUnderline);
+  format.setUnderlineColor(Qt::darkRed);
+  return format;
+}
+
+QTextCharFormat GetControlCharFormat()
+{
+  QTextCharFormat format;
+  format.setForeground(QBrush{Qt::darkGreen});
+  return format;
+}
+
+QTextCharFormat GetVariableCharFormat()
+{
+  QTextCharFormat format;
+  format.setForeground(QBrush{Qt::darkYellow});
+  return format;
+}
+
+QTextCharFormat GetBarewordCharFormat()
+{
+  QTextCharFormat format;
+  format.setForeground(QBrush{Qt::darkBlue});
+  return format;
+}
+
+QTextCharFormat GetCommentCharFormat()
+{
+  QTextCharFormat format;
+  format.setForeground(QBrush{Qt::darkGray});
+  return format;
+}
+}  // namespace
+
+ControlExpressionSyntaxHighlighter::ControlExpressionSyntaxHighlighter(QTextDocument* parent,
+                                                                       QLineEdit* result)
+    : QSyntaxHighlighter(parent), m_result_text(result)
+{
+}
+
+void ControlExpressionSyntaxHighlighter::highlightBlock(const QString&)
+{
+  // TODO: This is going to result in improper highlighting with non-ascii characters:
+  ciface::ExpressionParser::Lexer lexer(document()->toPlainText().toStdString());
+
+  std::vector<ciface::ExpressionParser::Token> tokens;
+  const auto tokenize_status = lexer.Tokenize(tokens);
+
+  using ciface::ExpressionParser::TokenType;
+
+  const auto set_block_format = [this](int start, int count, const QTextCharFormat& format) {
+    if (start + count <= currentBlock().position() ||
+        start >= currentBlock().position() + currentBlock().length())
+    {
+      // This range is not within the current block.
+      return;
+    }
+
+    int block_start = start - currentBlock().position();
+
+    if (block_start < 0)
+    {
+      count += block_start;
+      block_start = 0;
+    }
+
+    setFormat(block_start, count, format);
+  };
+
+  for (auto& token : tokens)
+  {
+    std::optional<QTextCharFormat> char_format;
+
+    switch (token.type)
+    {
+    case TokenType::TOK_INVALID:
+      char_format = GetInvalidCharFormat();
+      break;
+    case TokenType::TOK_LPAREN:
+    case TokenType::TOK_RPAREN:
+    case TokenType::TOK_COMMA:
+      char_format = GetSpecialCharFormat();
+      break;
+    case TokenType::TOK_LITERAL:
+      char_format = GetLiteralCharFormat();
+      break;
+    case TokenType::TOK_CONTROL:
+      char_format = GetControlCharFormat();
+      break;
+    case TokenType::TOK_BAREWORD:
+      char_format = GetBarewordCharFormat();
+      break;
+    case TokenType::TOK_VARIABLE:
+      char_format = GetVariableCharFormat();
+      break;
+    case TokenType::TOK_COMMENT:
+      char_format = GetCommentCharFormat();
+      break;
+    default:
+      if (token.IsBinaryOperator())
+        char_format = GetSpecialCharFormat();
+      break;
+    }
+
+    if (char_format.has_value())
+      set_block_format(int(token.string_position), int(token.string_length), *char_format);
+  }
+
+  // This doesn't need to be run for every "block", but it works.
+  if (ciface::ExpressionParser::ParseStatus::Successful != tokenize_status)
+  {
+    m_result_text->setText(tr("Invalid Token."));
+  }
+  else
+  {
+    ciface::ExpressionParser::RemoveInertTokens(&tokens);
+    const auto parse_status = ciface::ExpressionParser::ParseTokens(tokens);
+
+    m_result_text->setText(
+        QString::fromStdString(parse_status.description.value_or(_trans("Success."))));
+
+    if (ciface::ExpressionParser::ParseStatus::Successful != parse_status.status)
+    {
+      const auto token = *parse_status.token;
+      set_block_format(int(token.string_position), int(token.string_length),
+                       GetInvalidCharFormat());
+    }
+  }
+}
+
 IOWindow::IOWindow(QWidget* parent, ControllerEmu::EmulatedController* controller,
                    ControlReference* ref, IOWindow::Type type)
     : QDialog(parent), m_reference(ref), m_controller(controller), m_type(type)
 {
   CreateMainLayout();
-  ConnectWidgets();
 
   setWindowTitle(type == IOWindow::Type::Input ? tr("Configure Input") : tr("Configure Output"));
   setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
 
   ConfigChanged();
+
+  ConnectWidgets();
 }
 
 void IOWindow::CreateMainLayout()
@@ -51,18 +206,54 @@ void IOWindow::CreateMainLayout()
   m_option_list = new QListWidget();
   m_select_button = new QPushButton(tr("Select"));
   m_detect_button = new QPushButton(tr("Detect"));
-  m_or_button = new QPushButton(tr("| OR"));
-  m_and_button = new QPushButton(tr("&& AND"));
-  m_add_button = new QPushButton(tr("+ ADD"));
-  m_not_button = new QPushButton(tr("! NOT"));
   m_test_button = new QPushButton(tr("Test"));
-  m_expression_text = new QPlainTextEdit();
   m_button_box = new QDialogButtonBox();
   m_clear_button = new QPushButton(tr("Clear"));
   m_apply_button = new QPushButton(tr("Apply"));
   m_range_slider = new QSlider(Qt::Horizontal);
   m_range_spinbox = new QSpinBox();
 
+  m_parse_text = new QLineEdit();
+  m_parse_text->setReadOnly(true);
+
+  m_expression_text = new QPlainTextEdit();
+  m_expression_text->setFont(QFontDatabase::systemFont(QFontDatabase::FixedFont));
+  new ControlExpressionSyntaxHighlighter(m_expression_text->document(), m_parse_text);
+
+  m_operators_combo = new QComboBox();
+  m_operators_combo->addItem(tr("Operators"));
+  m_operators_combo->insertSeparator(1);
+  if (m_type == Type::Input)
+  {
+    m_operators_combo->addItem(tr("! Not"));
+    m_operators_combo->addItem(tr("* Multiply"));
+    m_operators_combo->addItem(tr("/ Divide"));
+    m_operators_combo->addItem(tr("% Modulo"));
+    m_operators_combo->addItem(tr("+ Add"));
+    m_operators_combo->addItem(tr("- Subtract"));
+    m_operators_combo->addItem(tr("> Greater-than"));
+    m_operators_combo->addItem(tr("< Less-than"));
+    m_operators_combo->addItem(tr("& And"));
+  }
+  m_operators_combo->addItem(tr("| Or"));
+  if (m_type == Type::Input)
+  {
+    m_operators_combo->addItem(tr(", Comma"));
+  }
+
+  m_functions_combo = new QComboBox();
+  m_functions_combo->addItem(tr("Functions"));
+  m_functions_combo->insertSeparator(1);
+  m_functions_combo->addItem(QStringLiteral("if"));
+  m_functions_combo->addItem(QStringLiteral("timer"));
+  m_functions_combo->addItem(QStringLiteral("toggle"));
+  m_functions_combo->addItem(QStringLiteral("deadzone"));
+  m_functions_combo->addItem(QStringLiteral("smooth"));
+  m_functions_combo->addItem(QStringLiteral("hold"));
+  m_functions_combo->addItem(QStringLiteral("tap"));
+  m_functions_combo->addItem(QStringLiteral("relative"));
+  m_functions_combo->addItem(QStringLiteral("pulse"));
+
   // Devices
   m_main_layout->addWidget(m_devices_combo);
 
@@ -77,16 +268,6 @@ void IOWindow::CreateMainLayout()
   m_range_spinbox->setMaximum(500);
   m_main_layout->addLayout(range_hbox);
 
-  // Options (Buttons, Outputs) and action buttons
-  // macOS style doesn't support expanding buttons
-#ifndef __APPLE__
-  for (QPushButton* button : {m_select_button, m_detect_button, m_or_button, m_and_button,
-                              m_add_button, m_not_button, m_test_button})
-  {
-    button->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
-  }
-#endif
-
   auto* hbox = new QHBoxLayout();
   auto* button_vbox = new QVBoxLayout();
   hbox->addWidget(m_option_list, 8);
@@ -94,17 +275,15 @@ void IOWindow::CreateMainLayout()
 
   button_vbox->addWidget(m_select_button);
   button_vbox->addWidget(m_type == Type::Input ? m_detect_button : m_test_button);
-  button_vbox->addWidget(m_or_button);
-
+  button_vbox->addWidget(m_operators_combo);
   if (m_type == Type::Input)
   {
-    button_vbox->addWidget(m_and_button);
-    button_vbox->addWidget(m_add_button);
-    button_vbox->addWidget(m_not_button);
+    button_vbox->addWidget(m_functions_combo);
   }
 
   m_main_layout->addLayout(hbox, 2);
   m_main_layout->addWidget(m_expression_text, 1);
+  m_main_layout->addWidget(m_parse_text);
 
   // Button Box
   m_main_layout->addWidget(m_button_box);
@@ -132,11 +311,7 @@ void IOWindow::ConfigChanged()
 
 void IOWindow::ConnectWidgets()
 {
-  connect(m_select_button, &QPushButton::clicked, [this] { AppendSelectedOption(""); });
-  connect(m_add_button, &QPushButton::clicked, [this] { AppendSelectedOption(" + "); });
-  connect(m_and_button, &QPushButton::clicked, [this] { AppendSelectedOption(" & "); });
-  connect(m_or_button, &QPushButton::clicked, [this] { AppendSelectedOption(" | "); });
-  connect(m_not_button, &QPushButton::clicked, [this] { AppendSelectedOption("!"); });
+  connect(m_select_button, &QPushButton::clicked, [this] { AppendSelectedOption(); });
 
   connect(m_detect_button, &QPushButton::clicked, this, &IOWindow::OnDetectButtonPressed);
   connect(m_test_button, &QPushButton::clicked, this, &IOWindow::OnTestButtonPressed);
@@ -147,17 +322,38 @@ void IOWindow::ConnectWidgets()
           this, &IOWindow::OnRangeChanged);
   connect(m_range_slider, static_cast<void (QSlider::*)(int value)>(&QSlider::valueChanged), this,
           &IOWindow::OnRangeChanged);
+
+  connect(m_expression_text, &QPlainTextEdit::textChanged, [this] {
+    m_apply_button->setText(m_apply_button->text().remove(QStringLiteral("*")));
+    m_apply_button->setText(m_apply_button->text() + QStringLiteral("*"));
+  });
+
+  connect(m_operators_combo, QOverload<int>::of(&QComboBox::activated), [this](int index) {
+    if (0 == index)
+      return;
+
+    m_expression_text->insertPlainText(m_operators_combo->currentText().left(1));
+
+    m_operators_combo->setCurrentIndex(0);
+  });
+
+  connect(m_functions_combo, QOverload<int>::of(&QComboBox::activated), [this](int index) {
+    if (0 == index)
+      return;
+
+    m_expression_text->insertPlainText(m_functions_combo->currentText() + QStringLiteral("()"));
+
+    m_functions_combo->setCurrentIndex(0);
+  });
 }
 
-void IOWindow::AppendSelectedOption(const std::string& prefix)
+void IOWindow::AppendSelectedOption()
 {
   if (m_option_list->currentItem() == nullptr)
     return;
 
-  m_expression_text->insertPlainText(
-      QString::fromStdString(prefix) +
-      MappingCommon::GetExpressionForControl(m_option_list->currentItem()->text(), m_devq,
-                                             m_controller->GetDefaultDevice()));
+  m_expression_text->insertPlainText(MappingCommon::GetExpressionForControl(
+      m_option_list->currentItem()->text(), m_devq, m_controller->GetDefaultDevice()));
 }
 
 void IOWindow::OnDeviceChanged(const QString& device)
@@ -175,7 +371,19 @@ void IOWindow::OnDialogButtonPressed(QAbstractButton* button)
   }
 
   m_reference->SetExpression(m_expression_text->toPlainText().toStdString());
-  m_controller->UpdateReferences(g_controller_interface);
+  m_controller->UpdateSingleControlReference(g_controller_interface, m_reference);
+
+  m_apply_button->setText(m_apply_button->text().remove(QStringLiteral("*")));
+
+  if (ciface::ExpressionParser::ParseStatus::SyntaxError == m_reference->GetParseStatus())
+  {
+    QMessageBox error(this);
+    error.setIcon(QMessageBox::Critical);
+    error.setWindowTitle(tr("Error"));
+    error.setText(tr("The expression contains a syntax error."));
+    error.setWindowModality(Qt::WindowModal);
+    error.exec();
+  }
 
   if (button != m_apply_button)
     accept();

Source/Core/DolphinQt/Config/Mapping/IOWindow.h

@@ -6,6 +6,7 @@
 
 #include <QDialog>
 #include <QString>
+#include <QSyntaxHighlighter>
 
 #include "Common/Flag.h"
 #include "InputCommon/ControllerInterface/Device.h"
@@ -14,6 +15,7 @@ class ControlReference;
 class QAbstractButton;
 class QComboBox;
 class QDialogButtonBox;
+class QLineEdit;
 class QListWidget;
 class QVBoxLayout;
 class QWidget;
@@ -27,6 +29,19 @@ namespace ControllerEmu
 class EmulatedController;
 }
 
+class ControlExpressionSyntaxHighlighter final : public QSyntaxHighlighter
+{
+  Q_OBJECT
+public:
+  ControlExpressionSyntaxHighlighter(QTextDocument* parent, QLineEdit* result);
+
+protected:
+  void highlightBlock(const QString& text) final override;
+
+private:
+  QLineEdit* const m_result_text;
+};
+
 class IOWindow final : public QDialog
 {
   Q_OBJECT
@@ -51,7 +66,7 @@ private:
   void OnTestButtonPressed();
   void OnRangeChanged(int range);
 
-  void AppendSelectedOption(const std::string& prefix);
+  void AppendSelectedOption();
   void UpdateOptionList();
   void UpdateDeviceList();
 
@@ -70,19 +85,18 @@ private:
 
   // Shared actions
   QPushButton* m_select_button;
-  QPushButton* m_or_button;
+  QComboBox* m_operators_combo;
 
   // Input actions
   QPushButton* m_detect_button;
-  QPushButton* m_and_button;
-  QPushButton* m_not_button;
-  QPushButton* m_add_button;
+  QComboBox* m_functions_combo;
 
   // Output actions
   QPushButton* m_test_button;
 
   // Textarea
   QPlainTextEdit* m_expression_text;
+  QLineEdit* m_parse_text;
 
   // Buttonbox
   QDialogButtonBox* m_button_box;

Source/Core/DolphinQt/Config/Mapping/MappingButton.cpp

@@ -100,7 +100,7 @@ void MappingButton::Detect()
     return;
 
   m_reference->SetExpression(expression.toStdString());
-  m_parent->GetController()->UpdateReferences(g_controller_interface);
+  m_parent->GetController()->UpdateSingleControlReference(g_controller_interface, m_reference);
 
   ConfigChanged();
   m_parent->SaveSettings();
@@ -111,7 +111,7 @@ void MappingButton::Clear()
   m_reference->range = 100.0 / SLIDER_TICK_COUNT;
 
   m_reference->SetExpression("");
-  m_parent->GetController()->UpdateReferences(g_controller_interface);
+  m_parent->GetController()->UpdateSingleControlReference(g_controller_interface, m_reference);
 
   m_parent->SaveSettings();
   ConfigChanged();

Source/Core/InputCommon/CMakeLists.txt

@@ -45,6 +45,8 @@ add_library(inputcommon
   ControlReference/ControlReference.h
   ControlReference/ExpressionParser.cpp
   ControlReference/ExpressionParser.h
+  ControlReference/FunctionExpression.cpp
+  ControlReference/FunctionExpression.h
 )
 
 target_link_libraries(inputcommon PUBLIC

Source/Core/InputCommon/ControlReference/ControlReference.cpp

@@ -25,12 +25,12 @@ bool ControlReference::InputGateOn()
 // Updates a controlreference's binded devices/controls
 // need to call this to re-bind a control reference after changing its expression
 //
-void ControlReference::UpdateReference(const ciface::Core::DeviceContainer& devices,
-                                       const ciface::Core::DeviceQualifier& default_device)
+void ControlReference::UpdateReference(ciface::ExpressionParser::ControlEnvironment& env)
 {
-  ControlFinder finder(devices, default_device, IsInput());
   if (m_parsed_expression)
-    m_parsed_expression->UpdateReferences(finder);
+  {
+    m_parsed_expression->UpdateReferences(env);
+  }
 }
 
 int ControlReference::BoundCount() const
@@ -54,7 +54,9 @@ std::string ControlReference::GetExpression() const
 void ControlReference::SetExpression(std::string expr)
 {
   m_expression = std::move(expr);
-  std::tie(m_parse_status, m_parsed_expression) = ParseExpression(m_expression);
+  auto parse_result = ParseExpression(m_expression);
+  m_parse_status = parse_result.status;
+  m_parsed_expression = std::move(parse_result.expr);
 }
 
 ControlReference::ControlReference() : range(1), m_parsed_expression(nullptr)

Source/Core/InputCommon/ControlReference/ControlReference.h

@@ -30,8 +30,7 @@ public:
 
   int BoundCount() const;
   ciface::ExpressionParser::ParseStatus GetParseStatus() const;
-  void UpdateReference(const ciface::Core::DeviceContainer& devices,
-                       const ciface::Core::DeviceQualifier& default_device);
+  void UpdateReference(ciface::ExpressionParser::ControlEnvironment& env);
   std::string GetExpression() const;
   void SetExpression(std::string expr);
 

Source/Core/InputCommon/ControlReference/ExpressionParser.h

@@ -4,56 +4,58 @@
 
 #pragma once
 
+#include <map>
 #include <memory>
+#include <optional>
 #include <string>
-#include <utility>
+
 #include "InputCommon/ControllerInterface/Device.h"
 
 namespace ciface::ExpressionParser
 {
-class ControlQualifier
+enum TokenType
 {
-public:
-  bool has_device;
-  Core::DeviceQualifier device_qualifier;
-  std::string control_name;
-
-  ControlQualifier() : has_device(false) {}
-  operator std::string() const
-  {
-    if (has_device)
-      return device_qualifier.ToString() + ":" + control_name;
-    else
-      return control_name;
-  }
+  TOK_WHITESPACE,
+  TOK_INVALID,
+  TOK_EOF,
+  TOK_LPAREN,
+  TOK_RPAREN,
+  TOK_NOT,
+  TOK_CONTROL,
+  TOK_LITERAL,
+  TOK_VARIABLE,
+  TOK_BAREWORD,
+  TOK_COMMENT,
+  // Binary Ops:
+  TOK_BINARY_OPS_BEGIN,
+  TOK_AND = TOK_BINARY_OPS_BEGIN,
+  TOK_OR,
+  TOK_ADD,
+  TOK_SUB,
+  TOK_MUL,
+  TOK_DIV,
+  TOK_MOD,
+  TOK_ASSIGN,
+  TOK_LTHAN,
+  TOK_GTHAN,
+  TOK_COMMA,
+  TOK_BINARY_OPS_END,
 };
 
-class ControlFinder
+class Token
 {
 public:
-  ControlFinder(const Core::DeviceContainer& container_, const Core::DeviceQualifier& default_,
-                const bool is_input_)
-      : container(container_), default_device(default_), is_input(is_input_)
-  {
-  }
-  std::shared_ptr<Core::Device> FindDevice(ControlQualifier qualifier) const;
-  Core::Device::Control* FindControl(ControlQualifier qualifier) const;
+  TokenType type;
+  std::string data;
 
-private:
-  const Core::DeviceContainer& container;
-  const Core::DeviceQualifier& default_device;
-  bool is_input;
-};
+  // Position in the input string:
+  std::size_t string_position = 0;
+  std::size_t string_length = 0;
 
-class Expression
-{
-public:
-  virtual ~Expression() = default;
-  virtual ControlState GetValue() const = 0;
-  virtual void SetValue(ControlState state) = 0;
-  virtual int CountNumControls() const = 0;
-  virtual void UpdateReferences(ControlFinder& finder) = 0;
-  virtual operator std::string() const = 0;
+  explicit Token(TokenType type_);
+  Token(TokenType type_, std::string data_);
+
+  bool IsBinaryOperator() const;
 };
 
 enum class ParseStatus
@@ -63,5 +65,129 @@ enum class ParseStatus
   EmptyExpression,
 };
 
-std::pair<ParseStatus, std::unique_ptr<Expression>> ParseExpression(const std::string& expr);
+class Lexer
+{
+public:
+  std::string expr;
+  std::string::iterator it;
+
+  explicit Lexer(std::string expr_);
+
+  ParseStatus Tokenize(std::vector<Token>& tokens);
+
+private:
+  template <typename F>
+  std::string FetchCharsWhile(F&& func)
+  {
+    std::string value;
+    while (it != expr.end() && func(*it))
+    {
+      value += *it;
+      ++it;
+    }
+    return value;
+  }
+
+  std::string FetchDelimString(char delim);
+  std::string FetchWordChars();
+  Token GetDelimitedLiteral();
+  Token GetVariable();
+  Token GetFullyQualifiedControl();
+  Token GetBareword(char c);
+  Token GetRealLiteral(char c);
+
+  Token PeekToken();
+  Token NextToken();
+};
+
+class ControlQualifier
+{
+public:
+  bool has_device;
+  Core::DeviceQualifier device_qualifier;
+  std::string control_name;
+
+  ControlQualifier() : has_device(false) {}
+
+  operator std::string() const
+  {
+    if (has_device)
+      return device_qualifier.ToString() + ":" + control_name;
+    else
+      return control_name;
+  }
+
+  void FromString(const std::string& str)
+  {
+    const auto col_pos = str.find_last_of(':');
+
+    has_device = (str.npos != col_pos);
+    if (has_device)
+    {
+      device_qualifier.FromString(str.substr(0, col_pos));
+      control_name = str.substr(col_pos + 1);
+    }
+    else
+    {
+      device_qualifier.FromString("");
+      control_name = str;
+    }
+  }
+};
+
+class ControlEnvironment
+{
+public:
+  using VariableContainer = std::map<std::string, ControlState>;
+
+  ControlEnvironment(const Core::DeviceContainer& container_, const Core::DeviceQualifier& default_,
+                     VariableContainer& vars)
+      : m_variables(vars), container(container_), default_device(default_)
+  {
+  }
+
+  std::shared_ptr<Core::Device> FindDevice(ControlQualifier qualifier) const;
+  Core::Device::Input* FindInput(ControlQualifier qualifier) const;
+  Core::Device::Output* FindOutput(ControlQualifier qualifier) const;
+  ControlState* GetVariablePtr(const std::string& name);
+
+private:
+  VariableContainer& m_variables;
+  const Core::DeviceContainer& container;
+  const Core::DeviceQualifier& default_device;
+};
+
+class Expression
+{
+public:
+  virtual ~Expression() = default;
+  virtual ControlState GetValue() const = 0;
+  virtual void SetValue(ControlState state) = 0;
+  virtual int CountNumControls() const = 0;
+  virtual void UpdateReferences(ControlEnvironment& finder) = 0;
+};
+
+class ParseResult
+{
+public:
+  static ParseResult MakeEmptyResult();
+  static ParseResult MakeSuccessfulResult(std::unique_ptr<Expression>&& expr);
+  static ParseResult MakeErrorResult(Token token, std::string description);
+
+  ParseStatus status;
+  std::unique_ptr<Expression> expr;
+
+  // Used for parse errors:
+  // TODO: This should probably be moved elsewhere:
+  std::optional<Token> token;
+  std::optional<std::string> description;
+
+private:
+  ParseResult() = default;
+};
+
+ParseResult ParseExpression(const std::string& expr);
+ParseResult ParseTokens(const std::vector<Token>& tokens);
+void RemoveInertTokens(std::vector<Token>* tokens);
+
 }  // namespace ciface::ExpressionParser

Source/Core/InputCommon/ControlReference/FunctionExpression.h

@@ -0,0 +1,55 @@
+// Copyright 2019 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+#include <string>
+#include <variant>
+#include <vector>
+
+#include "InputCommon/ControlReference/ExpressionParser.h"
+#include "InputCommon/ControlReference/FunctionExpression.h"
+
+namespace ciface
+{
+namespace ExpressionParser
+{
+class FunctionExpression : public Expression
+{
+public:
+  struct ArgumentsAreValid
+  {
+  };
+
+  struct ExpectedArguments
+  {
+    std::string text;
+  };
+
+  using ArgumentValidation = std::variant<ArgumentsAreValid, ExpectedArguments>;
+
+  int CountNumControls() const override;
+  void UpdateReferences(ControlEnvironment& env) override;
+
+  ArgumentValidation SetArguments(std::vector<std::unique_ptr<Expression>>&& args);
+
+  void SetValue(ControlState value) override;
+
+protected:
+  virtual ArgumentValidation
+  ValidateArguments(const std::vector<std::unique_ptr<Expression>>& args) = 0;
+
+  Expression& GetArg(u32 number);
+  const Expression& GetArg(u32 number) const;
+  u32 GetArgCount() const;
+
+private:
+  std::vector<std::unique_ptr<Expression>> m_args;
+};
+
+std::unique_ptr<FunctionExpression> MakeFunctionExpression(std::string name);
+
+}  // namespace ExpressionParser
+}  // namespace ciface

Source/Core/InputCommon/ControllerEmu/ControllerEmu.cpp

@@ -38,23 +38,38 @@ std::unique_lock<std::recursive_mutex> EmulatedController::GetStateLock()
 
 void EmulatedController::UpdateReferences(const ControllerInterface& devi)
 {
-  const auto lock = GetStateLock();
   m_default_device_is_connected = devi.HasConnectedDevice(m_default_device);
 
+  ciface::ExpressionParser::ControlEnvironment env(devi, GetDefaultDevice(), m_expression_vars);
+
+  UpdateReferences(env);
+}
+
+void EmulatedController::UpdateReferences(ciface::ExpressionParser::ControlEnvironment& env)
+{
+  const auto lock = GetStateLock();
+
   for (auto& ctrlGroup : groups)
   {
     for (auto& control : ctrlGroup->controls)
-      control->control_ref.get()->UpdateReference(devi, GetDefaultDevice());
+      control->control_ref->UpdateReference(env);
 
     // Attachments:
     if (ctrlGroup->type == GroupType::Attachments)
     {
       for (auto& attachment : static_cast<Attachments*>(ctrlGroup.get())->GetAttachmentList())
-        attachment->UpdateReferences(devi);
+        attachment->UpdateReferences(env);
     }
   }
 }
 
+void EmulatedController::UpdateSingleControlReference(const ControllerInterface& devi,
+                                                      ControlReference* ref)
+{
+  ciface::ExpressionParser::ControlEnvironment env(devi, GetDefaultDevice(), m_expression_vars);
+  ref->UpdateReference(env);
+}
+
 bool EmulatedController::IsDefaultDeviceConnected() const
 {
   return m_default_device_is_connected;

Source/Core/InputCommon/ControllerEmu/ControllerEmu.h

@@ -13,6 +13,7 @@
 
 #include "Common/Common.h"
 #include "Common/IniFile.h"
+#include "InputCommon/ControlReference/ExpressionParser.h"
 #include "InputCommon/ControllerInterface/Device.h"
 
 class ControllerInterface;
@@ -20,6 +21,8 @@ class ControllerInterface;
 const char* const named_directions[] = {_trans("Up"), _trans("Down"), _trans("Left"),
                                         _trans("Right")};
 
+class ControlReference;
+
 namespace ControllerEmu
 {
 class ControlGroup;
@@ -43,6 +46,7 @@ public:
   void SetDefaultDevice(ciface::Core::DeviceQualifier devq);
 
   void UpdateReferences(const ControllerInterface& devi);
+  void UpdateSingleControlReference(const ControllerInterface& devi, ControlReference* ref);
 
   // This returns a lock that should be held before calling State() on any control
   // references and GetState(), by extension. This prevents a race condition
@@ -75,6 +79,12 @@ public:
       return T(std::lround((zero_value - neg_1_value) * input_value + zero_value));
   }
 
+protected:
+  // TODO: Wiimote attachment has its own member that isn't being used..
+  ciface::ExpressionParser::ControlEnvironment::VariableContainer m_expression_vars;
+
+  void UpdateReferences(ciface::ExpressionParser::ControlEnvironment& env);
+
 private:
   ciface::Core::DeviceQualifier m_default_device;
   bool m_default_device_is_connected{false};

Source/Core/InputCommon/InputCommon.vcxproj

@@ -64,6 +64,7 @@
     <ClCompile Include="ControllerInterface\ForceFeedback\ForceFeedbackDevice.cpp" />
     <ClCompile Include="ControllerInterface\Win32\Win32.cpp" />
     <ClCompile Include="ControllerInterface\XInput\XInput.cpp" />
+    <ClCompile Include="ControlReference\FunctionExpression.cpp" />
     <ClCompile Include="GCAdapter.cpp">
       <!--
       Disable "nonstandard extension used : zero-sized array in struct/union" warning,
@@ -100,6 +101,7 @@
     <ClInclude Include="ControllerInterface\DInput\DInputKeyboardMouse.h" />
     <ClInclude Include="ControllerInterface\DInput\XInputFilter.h" />
     <ClInclude Include="ControlReference\ControlReference.h" />
+    <ClInclude Include="ControlReference\FunctionExpression.h" />
     <ClInclude Include="ControlReference\ExpressionParser.h" />
     <ClInclude Include="ControllerInterface\ForceFeedback\ForceFeedbackDevice.h" />
     <ClInclude Include="ControllerInterface\Win32\Win32.h" />

Source/Core/InputCommon/InputCommon.vcxproj.filters

@@ -113,6 +113,9 @@
     <ClCompile Include="ControlReference\ControlReference.cpp">
       <Filter>ControllerInterface</Filter>
     </ClCompile>
+    <ClCompile Include="ControlReference\FunctionExpression.cpp">
+      <Filter>ControllerInterface</Filter>
+    </ClCompile>
     <ClCompile Include="InputProfile.cpp" />
     <ClCompile Include="ControllerEmu\ControlGroup\Attachments.cpp">
       <Filter>ControllerEmu\ControlGroup</Filter>
@@ -206,6 +209,9 @@
     <ClInclude Include="ControlReference\ControlReference.h">
       <Filter>ControllerInterface</Filter>
     </ClInclude>
+    <ClCompile Include="ControlReference\FunctionExpression.h">
+      <Filter>ControllerInterface</Filter>
+    </ClCompile>
     <ClInclude Include="InputProfile.h" />
     <ClInclude Include="ControllerEmu\ControlGroup\Attachments.h">
       <Filter>ControllerEmu\ControlGroup</Filter>