Finish dirty first pass over parser

src/parse/error.rs

@@ -28,6 +28,7 @@ pub enum Kind
 	UnexpectedToken,
 	EmptyExpression,
 	ExpectedLogicalConnectiveArgument(String),
+	ExpectedTerm,
 	MultipleComparisonOperators(crate::ComparisonOperator, crate::ComparisonOperator),
 }
 
@@ -101,6 +102,11 @@ impl Error
 		Self::new(Kind::ExpectedLogicalConnectiveArgument(logical_connective_name), location)
 	}
 
+	pub(crate) fn new_expected_term(location: Location) -> Self
+	{
+		Self::new(Kind::ExpectedTerm, location)
+	}
+
 	pub(crate) fn new_multiple_comparison_operators(
 		comparison_operator_1: crate::ComparisonOperator,
 		comparison_operator_2: crate::ComparisonOperator, location: Location)
@@ -134,12 +140,13 @@ impl std::fmt::Debug for Error
 			Kind::MixedImplicationDirections(_location_2) =>
 				write!(formatter, "-> and <- implications may not be mixed within the same scope")?,
 			Kind::ExpectedVariableDeclaration =>
-				write!(formatter, "expected variable declaration")?,
+				write!(formatter, "expected a variable declaration")?,
 			Kind::UnexpectedToken => write!(formatter, "unexpected token")?,
 			Kind::EmptyExpression => write!(formatter, "empty expression")?,
 			Kind::ExpectedLogicalConnectiveArgument(ref logical_connective_name) =>
 				write!(formatter, "this “{}” logical connective is missing an argument",
 					logical_connective_name)?,
+			Kind::ExpectedTerm => write!(formatter, "expected a term")?,
 			Kind::MultipleComparisonOperators(comparison_operator_1, comparison_operator_2) =>
 				write!(formatter, "chained comparisons aren’t supported (found “{:?}” and “{:?}” in the same formula), consider separating them with “and”",
 					comparison_operator_1, comparison_operator_2)?,

src/parse/formulas.rs

@@ -68,28 +68,15 @@ impl<'i> FormulaStr<'i>
 		}
 	}
 
-	fn tokens(&self) -> Tokens<'i, impl FnMut(Token<'i>) -> Option<Token<'i>>>
-	{
-		Tokens::new_iter(self.input)
-	}
-
 	fn logical_connectives(&self) -> Tokens<'i, impl FnMut(Token<'i>) -> Option<LogicalConnective>>
 	{
 		let functor = |token| match token
 		{
-			Token::Identifier(ref identifier) => match *identifier
-			{
-				"and" => Some(LogicalConnective::And),
-				"or" => Some(LogicalConnective::Or),
-				_ => None,
-			},
-			Token::Symbol(ref symbol) => match symbol
-			{
-				Symbol::ArrowLeft => Some(LogicalConnective::ImpliesRightToLeft),
-				Symbol::ArrowLeftAndRight => Some(LogicalConnective::IfAndOnlyIf),
-				Symbol::ArrowRight => Some(LogicalConnective::ImpliesLeftToRight),
-				_ => None,
-			},
+			Token::Identifier("and") => Some(LogicalConnective::And),
+			Token::Identifier("or") => Some(LogicalConnective::Or),
+			Token::Symbol(Symbol::ArrowLeft) => Some(LogicalConnective::ImpliesRightToLeft),
+			Token::Symbol(Symbol::ArrowLeftAndRight) => Some(LogicalConnective::IfAndOnlyIf),
+			Token::Symbol(Symbol::ArrowRight) => Some(LogicalConnective::ImpliesLeftToRight),
 			_ => None,
 		};
 
@@ -101,19 +88,14 @@ impl<'i> FormulaStr<'i>
 	{
 		let predicate = move |token: &_| match token
 		{
-			Token::Identifier(ref identifier) => match *identifier
-			{
-				"and" => logical_connective == LogicalConnective::And,
-				"or" => logical_connective == LogicalConnective::Or,
-				_ => false,
-			},
-			Token::Symbol(ref symbol) => match symbol
-			{
-				Symbol::ArrowLeft => logical_connective == LogicalConnective::ImpliesRightToLeft,
-				Symbol::ArrowLeftAndRight => logical_connective == LogicalConnective::IfAndOnlyIf,
-				Symbol::ArrowRight => logical_connective == LogicalConnective::ImpliesLeftToRight,
-				_ => false,
-			},
+			Token::Identifier("and") => logical_connective == LogicalConnective::And,
+			Token::Identifier("or") => logical_connective == LogicalConnective::Or,
+			Token::Symbol(Symbol::ArrowLeft) =>
+				logical_connective == LogicalConnective::ImpliesRightToLeft,
+			Token::Symbol(Symbol::ArrowLeftAndRight) =>
+				logical_connective == LogicalConnective::IfAndOnlyIf,
+			Token::Symbol(Symbol::ArrowRight) =>
+				logical_connective == LogicalConnective::ImpliesLeftToRight,
 			_ => false,
 		};
 
@@ -247,14 +229,38 @@ impl<'i> FormulaStr<'i>
 		// Parse quantified formulas
 		if let Some((identifier, input)) = identifier(input)
 		{
-			if identifier == "not"
+			match identifier
 			{
-				let input = input.trim_start();
-				println!("{}  parsing “not” formula body: {}", indentation, input);
+				"not" =>
+				{
+					let input = input.trim_start();
+					println!("{}  parsing “not” formula body: {}", indentation, input);
 
-				let argument = FormulaStr::new(input).parse(level + 1)?;
+					let argument = FormulaStr::new(input).parse(level + 1)?;
 
-				return Ok(crate::Formula::not(Box::new(argument)));
+					return Ok(crate::Formula::not(Box::new(argument)));
+				},
+				"true" =>
+				{
+					if !input.trim().is_empty()
+					{
+						return Err(crate::parse::Error::new_unexpected_token(
+							crate::parse::error::Location::new(0, Some(0))))
+					}
+
+					return Ok(crate::Formula::true_());
+				},
+				"false" =>
+				{
+					if !input.trim().is_empty()
+					{
+						return Err(crate::parse::Error::new_unexpected_token(
+							crate::parse::error::Location::new(0, Some(0))))
+					}
+
+					return Ok(crate::Formula::false_());
+				},
+				_ => (),
 			}
 
 			let quantifier = match identifier
@@ -340,25 +346,19 @@ impl<'i> FormulaStr<'i>
 				crate::PredicateDeclaration::new(predicate_name.to_string(), arguments.len());
 			let declaration = std::rc::Rc::new(declaration);
 
-			// TODO: handle unexpected input after end of parenthesized expression
-
 			return Ok(crate::Formula::predicate(declaration, arguments));
 		}
 
 		// Parse parenthesized formulas
-		match parenthesized_expression(input)?
+		if let Some((parenthesized_expression, input)) = parenthesized_expression(input)?
 		{
-			Some((parenthesized_expression, input)) =>
+			if !input.trim().is_empty()
 			{
-				if !input.trim().is_empty()
-				{
-					return Err(crate::parse::Error::new_unexpected_token(
-						crate::parse::error::Location::new(0, Some(0))));
-				}
+				return Err(crate::parse::Error::new_unexpected_token(
+					crate::parse::error::Location::new(0, Some(0))));
+			}
 
-				return FormulaStr::new(parenthesized_expression).parse(level);
-			},
-			None => (),
+			return FormulaStr::new(parenthesized_expression).parse(level + 1);
 		}
 
 		Err(crate::parse::Error::new_unexpected_token(

src/parse/terms.rs

@@ -49,6 +49,45 @@ fn variable_name(input: &str) -> Option<(&str, &str)>
 	None
 }
 
+pub fn is_function_name(identifier: &str) -> bool
+{
+	if is_keyword(identifier)
+	{
+		return false;
+	}
+
+	let mut characters = identifier.chars();
+
+	while let Some(character) = characters.next()
+	{
+		match character
+		{
+			'_' => continue,
+			_ if character.is_ascii_lowercase() => return true,
+			_ => return false,
+		}
+	}
+
+	false
+}
+
+fn is_variable_name(identifier: &str) -> bool
+{
+	let mut characters = identifier.chars();
+
+	while let Some(character) = characters.next()
+	{
+		match character
+		{
+			'_' => continue,
+			_ if character.is_ascii_uppercase() => return true,
+			_ => return false,
+		}
+	}
+
+	false
+}
+
 pub(crate) fn variable_declaration(input: &str) -> Option<(crate::VariableDeclaration, &str)>
 {
 	variable_name(input)
@@ -96,45 +135,35 @@ pub(crate) fn variable_declarations(input: &str)
 }
 
 #[derive(Clone, Copy, Eq, PartialEq)]
-pub(crate) enum TermInfixOperator
+pub(crate) enum ArithmeticOperatorClass
 {
-	Add,
-	Divide,
-	Exponentiate,
-	Modulo,
-	Multiply,
-	Subtract,
+	Exponential,
+	Multiplicative,
+	Additive,
 }
 
-impl TermInfixOperator
+impl ArithmeticOperatorClass
 {
 	fn level(&self) -> usize
 	{
 		match self
 		{
-			Self::Exponentiate => 1,
-			Self::Multiply
-			| Self::Divide
-			| Self::Modulo => 2,
-			Self::Add
-			| Self::Subtract => 3,
+			Self::Exponential => 1,
+			Self::Multiplicative => 2,
+			Self::Additive => 3,
 		}
 	}
 }
 
-impl std::fmt::Debug for TermInfixOperator
+impl std::fmt::Debug for ArithmeticOperatorClass
 {
 	fn fmt(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result
 	{
 		match &self
 		{
-			Self::Add => write!(formatter, "+"),
-			Self::Divide => write!(formatter, "/"),
-			Self::Exponentiate => write!(formatter, "**"),
-			// TODO: conflicts with single-line comments
-			Self::Modulo => write!(formatter, "%"),
-			Self::Multiply => write!(formatter, "*"),
-			Self::Subtract => write!(formatter, "-"),
+			Self::Exponential => write!(formatter, "exponential"),
+			Self::Multiplicative => write!(formatter, "multiplicative"),
+			Self::Additive => write!(formatter, "additive"),
 		}
 	}
 }
@@ -154,15 +183,118 @@ impl<'i> TermStr<'i>
 		}
 	}
 
-	pub fn iter_infix_operators(&self) -> TermInfixOperatorIterator<'i>
+	fn arithmetic_operator_classes(&self) -> Tokens<'i, impl FnMut(Token<'i>)
+		-> Option<ArithmeticOperatorClass>>
 	{
-		TermInfixOperatorIterator::new(self.input)
+		let functor = |token| match token
+		{
+			Token::Symbol(Symbol::Exponentiation) => Some(ArithmeticOperatorClass::Exponential),
+			Token::Symbol(Symbol::Multiplication) => Some(ArithmeticOperatorClass::Multiplicative),
+			Token::Symbol(Symbol::Division) => Some(ArithmeticOperatorClass::Multiplicative),
+			Token::Symbol(Symbol::Percent) => Some(ArithmeticOperatorClass::Multiplicative),
+			Token::Symbol(Symbol::Plus) => Some(ArithmeticOperatorClass::Additive),
+			Token::Symbol(Symbol::Minus) => Some(ArithmeticOperatorClass::Additive),
+			_ => None,
+		};
+
+		// TODO: refactor so that self.input is always set correctly
+		Tokens::new_filter_map(self.input, functor)
 	}
 
-	pub fn split_at_infix_operator(&self, infix_operator: TermInfixOperator)
-		-> SplitTermAtInfixOperator<'i>
+	fn filter_by_arithmetic_operator_class(&self,
+		arithmetic_operator_class: ArithmeticOperatorClass)
+		-> Tokens<'i, impl FnMut(Token<'i>) -> Option<crate::BinaryOperator>>
 	{
-		SplitTermAtInfixOperator::new(self, infix_operator)
+		let functor = move |token| match token
+		{
+			Token::Symbol(Symbol::Exponentiation) =>
+				if arithmetic_operator_class == ArithmeticOperatorClass::Exponential
+				{
+					Some(crate::BinaryOperator::Exponentiate)
+				}
+				else
+				{
+					None
+				},
+			Token::Symbol(Symbol::Multiplication) =>
+				if arithmetic_operator_class == ArithmeticOperatorClass::Multiplicative
+				{
+					Some(crate::BinaryOperator::Multiply)
+				}
+				else
+				{
+					None
+				},
+			Token::Symbol(Symbol::Division) =>
+				if arithmetic_operator_class == ArithmeticOperatorClass::Multiplicative
+				{
+					Some(crate::BinaryOperator::Divide)
+				}
+				else
+				{
+					None
+				},
+			Token::Symbol(Symbol::Percent) =>
+				if arithmetic_operator_class == ArithmeticOperatorClass::Multiplicative
+				{
+					Some(crate::BinaryOperator::Modulo)
+				}
+				else
+				{
+					None
+				},
+			Token::Symbol(Symbol::Plus) =>
+				if arithmetic_operator_class == ArithmeticOperatorClass::Additive
+				{
+					Some(crate::BinaryOperator::Add)
+				}
+				else
+				{
+					None
+				},
+			Token::Symbol(Symbol::Minus) =>
+				if arithmetic_operator_class == ArithmeticOperatorClass::Additive
+				{
+					Some(crate::BinaryOperator::Subtract)
+				}
+				else
+				{
+					None
+				},
+			_ => None,
+		};
+
+		Tokens::new_filter_map(self.input, functor)
+	}
+
+	pub fn top_level_arithmetic_operator_class(&self)
+		-> Result<Option<ArithmeticOperatorClass>, crate::parse::Error>
+	{
+		let mut top_level_arithmetic_operator_class = None;
+
+		for arithmetic_operator_class in self.arithmetic_operator_classes()
+		{
+			let (_, arithmetic_operator_class) = arithmetic_operator_class?;
+
+			top_level_arithmetic_operator_class = match top_level_arithmetic_operator_class
+			{
+				None => Some(arithmetic_operator_class),
+				Some(top_level_arithmetic_operator_class) =>
+				{
+					if arithmetic_operator_class.level()
+						> top_level_arithmetic_operator_class.level()
+					{
+						Some(arithmetic_operator_class)
+					}
+					else
+					{
+						Some(top_level_arithmetic_operator_class)
+					}
+				},
+			}
+		}
+
+		Ok(top_level_arithmetic_operator_class)
 	}
 
 	pub fn parse(&self, level: usize) -> Result<crate::Term, crate::parse::Error>
@@ -172,181 +304,235 @@ impl<'i> TermStr<'i>
 
 		let input = self.input.trim_start();
 
-		// TODO: implement
-		Ok(crate::Term::true_())
-	}
-}
-
-pub(crate) struct TermInfixOperatorIterator<'i>
-{
-	original_input: &'i str,
-	input: &'i str,
-}
-
-impl<'i> TermInfixOperatorIterator<'i>
-{
-	pub fn new(input: &'i str) -> Self
-	{
-		Self
+		match input.chars().next()
 		{
-			original_input: input,
-			input,
+			Some(')') => return Err(crate::parse::Error::new_unmatched_parenthesis(
+				crate::parse::error::Location::new(0, Some(0)))),
+			// TODO: implement absolute value function
+			Some('|') => unimplemented!(),
+			None => return Err(crate::parse::Error::new_empty_expression(
+				crate::parse::error::Location::new(0, Some(0)))),
+			_ => (),
 		}
-	}
-}
 
-impl<'i> std::iter::Iterator for TermInfixOperatorIterator<'i>
-{
-	type Item = Result<(&'i str, &'i str, TermInfixOperator), crate::parse::Error>;
-
-	fn next(&mut self) -> Option<Self::Item>
-	{
-		loop
+		// Parse arithmetic infix operations
+		if let Some(top_level_arithmetic_operator_class) =
+			self.top_level_arithmetic_operator_class()?
 		{
-			self.input = self.input.trim_start();
+			println!("{}  parsing {:?} arithmetic term", indentation,
+				top_level_arithmetic_operator_class);
 
-			let first_character = match self.input.chars().next()
+			if top_level_arithmetic_operator_class == ArithmeticOperatorClass::Exponential
 			{
-				None => return None,
-				Some(first_character) => first_character,
-			};
-
-			// TODO: implement
-			if self.input.starts_with("|")
-			{
-				unimplemented!();
+				return exponentiate(
+					self.filter_by_arithmetic_operator_class(top_level_arithmetic_operator_class)
+						.split(), level + 1);
 			}
 
-			if self.input.starts_with(")")
+			// Parse arguments of arithmetic infix operations
+			let mut argument_iterator =
+				self.filter_by_arithmetic_operator_class(top_level_arithmetic_operator_class);
+
+			let (first_argument, first_binary_operator) = argument_iterator.next().ok_or_else(||
+				crate::parse::Error::new_expected_term(
+					crate::parse::error::Location::new(0, Some(0))))??;
+			let first_argument = TermStr::new(first_argument).parse(level + 1)?;
+			// TODO: improve error handling if the terms between the operators are invalid
+
+			let (accumulator, last_binary_operator) =
+				argument_iterator.try_fold((first_argument, first_binary_operator),
+					|(accumulator, binary_operator), argument|
+					{
+						let (argument, next_binary_operator) = argument?;
+						let argument = TermStr::new(argument).parse(level + 1)?;
+						let binary_operation =
+							crate::BinaryOperation::new(binary_operator, Box::new(accumulator),
+								Box::new(argument));
+						let formula = crate::Term::BinaryOperation(binary_operation);
+
+						Ok((formula, next_binary_operator))
+					})?;
+
+			// The last item hasn’t been consumed yet, so it’s safe to unwrap it
+			let last_argument = argument_iterator.remaining_input().unwrap();
+			let last_argument = TermStr::new(last_argument).parse(level + 1)?;
+			let last_binary_operation =
+				crate::BinaryOperation::new(last_binary_operator, Box::new(accumulator),
+					Box::new(last_argument));
+
+			return Ok(crate::Term::BinaryOperation(last_binary_operation));
+		}
+
+		if let Some((number, input)) = number(input)?
+		{
+			if !input.trim().is_empty()
 			{
-				return Some(Err(crate::parse::Error::new_unmatched_parenthesis(
-					crate::parse::error::Location::new(0, Some(1)))));
+				return Err(crate::parse::Error::new_unexpected_token(
+					crate::parse::error::Location::new(0, Some(0))));
 			}
 
-			match parenthesized_expression(self.input)
+			return Ok(crate::Term::integer(number as i32));
+		}
+
+		if let Some((identifier, input)) = identifier(input)
+		{
+			match identifier
 			{
-				Ok(Some((_, remaining_input))) =>
+				"inf" =>
 				{
-					self.input = remaining_input;
-					continue;
+					if !input.trim().is_empty()
+					{
+						return Err(crate::parse::Error::new_unexpected_token(
+							crate::parse::error::Location::new(0, Some(0))))
+					}
+
+					return Ok(crate::Term::infimum());
 				},
-				Ok(None) => (),
-				Err(error) => return Some(Err(error)),
-			}
-
-			match number(self.input)
-			{
-				Ok(Some((_, remaining_input))) =>
+				"sup" =>
 				{
-					self.input = remaining_input;
-					continue;
-				}
-				Ok(None) => (),
-				Err(error) => return Some(Err(error)),
-			}
+					if !input.trim().is_empty()
+					{
+						return Err(crate::parse::Error::new_unexpected_token(
+							crate::parse::error::Location::new(0, Some(0))))
+					}
 
-			let index_left = self.input.as_ptr() as usize - self.original_input.as_ptr() as usize;
-			let input_left = self.original_input.split_at(index_left).0.trim_end();
-
-			if let Some((_, remaining_input)) = identifier(self.input)
-			{
-				self.input = remaining_input;
-				continue;
-			}
-
-			if let Some((symbol, remaining_input)) = symbol(self.input)
-			{
-				self.input = remaining_input;
-
-				match symbol
+					return Ok(crate::Term::supremum());
+				},
+				"true" =>
 				{
-					Symbol::Division => return Some(Ok((input_left, remaining_input,
-						TermInfixOperator::Divide))),
-					Symbol::Exponentiation => return Some(Ok((input_left, remaining_input,
-						TermInfixOperator::Exponentiate))),
-					Symbol::Minus => return Some(Ok((input_left, remaining_input,
-						TermInfixOperator::Subtract))),
-					Symbol::Multiplication => return Some(Ok((input_left, remaining_input,
-						TermInfixOperator::Multiply))),
-					Symbol::Percent => return Some(Ok((input_left, remaining_input,
-						TermInfixOperator::Modulo))),
-					Symbol::Plus => return Some(Ok((input_left, remaining_input,
-						TermInfixOperator::Add))),
-					_ => continue,
-				}
-			}
+					if !input.trim().is_empty()
+					{
+						return Err(crate::parse::Error::new_unexpected_token(
+							crate::parse::error::Location::new(0, Some(0))))
+					}
 
-			return Some(Err(crate::parse::Error::new_character_not_allowed(first_character,
-				crate::parse::error::Location::new(0, Some(0)))));
+					return Ok(crate::Term::true_());
+				},
+				"false" =>
+				{
+					if !input.trim().is_empty()
+					{
+						return Err(crate::parse::Error::new_unexpected_token(
+							crate::parse::error::Location::new(0, Some(0))))
+					}
+
+					return Ok(crate::Term::false_());
+				},
+				_ if is_variable_name(identifier) =>
+				{
+					if !input.trim().is_empty()
+					{
+						return Err(crate::parse::Error::new_unexpected_token(
+							crate::parse::error::Location::new(0, Some(0))))
+					}
+
+					// TODO: implement look-up
+					let declaration = crate::VariableDeclaration::new(identifier.to_string());
+					let declaration = std::rc::Rc::new(declaration);
+					return Ok(crate::Term::variable(declaration));
+				},
+				_ if is_function_name(identifier) =>
+				{
+					let function_name = identifier;
+					println!("{}  parsing function {}", indentation, function_name);
+
+					let input = input.trim_start();
+
+					// Parse arguments if there are any
+					let (arguments, input) = match parenthesized_expression(input)?
+					{
+						Some((parenthesized_expression, input)) =>
+						{
+							let functor = |token: &_| *token == Token::Symbol(Symbol::Comma);
+							let arguments = Tokens::new_filter(parenthesized_expression, functor).split()
+								.map(|argument| TermStr::new(argument?).parse(level + 1))
+								.collect::<Result<_, _>>()?;
+
+							(arguments, input)
+						}
+						None => (vec![], input),
+					};
+
+					if !input.trim().is_empty()
+					{
+						return Err(crate::parse::Error::new_unexpected_token(
+							crate::parse::error::Location::new(0, Some(0))))
+					}
+
+					// TODO: implement look-up
+					let declaration =
+						crate::FunctionDeclaration::new(function_name.to_string(), arguments.len());
+					let declaration = std::rc::Rc::new(declaration);
+
+					return Ok(crate::Term::function(declaration, arguments));
+				},
+				_ => (),
+			}
 		}
+
+		// TODO: parse negative value
+
+		// Parse parenthesized terms
+		if let Some((parenthesized_expression, input)) = parenthesized_expression(input)?
+		{
+			if !input.trim().is_empty()
+			{
+				return Err(crate::parse::Error::new_unexpected_token(
+					crate::parse::error::Location::new(0, Some(0))));
+			}
+
+			return TermStr::new(parenthesized_expression).parse(level + 1);
+		}
+
+		Err(crate::parse::Error::new_unexpected_token(
+			crate::parse::error::Location::new(0, Some(0))))
 	}
 }
 
-pub(crate) struct SplitTermAtInfixOperator<'i>
+// TODO: refactor
+fn exponentiate_inner<'i, T>(mut argument_iterator: T, level: usize)
+	-> Result<Option<crate::Term>, crate::parse::Error>
+where
+	T: std::iter::Iterator<Item = Result<&'i str, crate::parse::Error>>
 {
-	infix_operator_iterator: TermInfixOperatorIterator<'i>,
-	infix_operator: TermInfixOperator,
-	previous_index: usize,
-}
-
-impl<'i> SplitTermAtInfixOperator<'i>
-{
-	pub fn new(input: &TermStr<'i>, infix_operator: TermInfixOperator)
-		-> Self
+	match argument_iterator.next()
 	{
-		Self
+		Some(argument) =>
 		{
-			infix_operator_iterator: input.iter_infix_operators(),
-			infix_operator,
-			previous_index: 0,
-		}
+			// TODO: improve error handling if antecedent cannot be parsed
+			let argument = TermStr::new(argument?).parse(level)?;
+			match exponentiate_inner(argument_iterator, level)?
+			{
+				Some(next_argument) => Ok(Some(crate::Term::exponentiate(Box::new(argument),
+					Box::new(next_argument)))),
+				None => Ok(Some(argument)),
+			}
+		},
+		None => Ok(None),
 	}
 }
 
-impl<'i> std::iter::Iterator for SplitTermAtInfixOperator<'i>
+fn exponentiate<'i, T>(mut argument_iterator: T, level: usize)
+	-> Result<crate::Term, crate::parse::Error>
+where
+	T: std::iter::Iterator<Item = Result<&'i str, crate::parse::Error>>
 {
-	type Item = Result<&'i str, crate::parse::Error>;
-
-	fn next(&mut self) -> Option<Self::Item>
+	match argument_iterator.next()
 	{
-		loop
+		Some(argument) =>
 		{
-			let (input_left, input_right, infix_operator) =
-				match self.infix_operator_iterator.next()
+			// TODO: improve error handling if antecedent cannot be parsed
+			let argument = TermStr::new(argument?).parse(level)?;
+			match exponentiate_inner(argument_iterator, level)?
 			{
-				Some(Err(error)) => return Some(Err(error)),
-				Some(Ok(infix_operator_iterator_next)) => infix_operator_iterator_next,
-				None => break,
-			};
-
-			if infix_operator == self.infix_operator
-			{
-				// TODO: refactor
-				let index = input_left.as_ptr() as usize
-					+ input_left.len()
-					- self.infix_operator_iterator.original_input.as_ptr() as usize;
-				let split_input = &self.infix_operator_iterator
-					.original_input[self.previous_index..index].trim();
-				self.previous_index = input_right.as_ptr() as usize
-					- self.infix_operator_iterator.original_input.as_ptr() as usize;
-
-				return Some(Ok(split_input));
+				Some(next_argument) =>
+					Ok(crate::Term::exponentiate(Box::new(argument), Box::new(next_argument))),
+				None => Err(crate::parse::Error::new_expected_term(
+					crate::parse::error::Location::new(0, Some(0)))),
 			}
-		}
-
-		let remaining_input = self.infix_operator_iterator
-			.original_input[self.previous_index..].trim();
-
-		if remaining_input.is_empty()
-		{
-			None
-		}
-		else
-		{
-			self.previous_index = self.infix_operator_iterator.original_input.len();
-
-			Some(Ok(remaining_input))
-		}
+		},
+		None => Err(crate::parse::Error::new_expected_term(
+			crate::parse::error::Location::new(0, Some(0)))),
 	}
 }
 

src/parse/tokens.rs

@@ -10,8 +10,10 @@ pub(crate) enum Keyword
 	Exists,
 	False,
 	ForAll,
+	Infimum,
 	Not,
 	Or,
+	Supremum,
 	True,
 }
 
@@ -25,8 +27,10 @@ impl std::fmt::Debug for Keyword
 			Self::Exists => write!(formatter, "exists"),
 			Self::False => write!(formatter, "false"),
 			Self::ForAll => write!(formatter, "forall"),
+			Self::Infimum => write!(formatter, "inf"),
 			Self::Not => write!(formatter, "not"),
 			Self::Or => write!(formatter, "or"),
+			Self::Supremum => write!(formatter, "sup"),
 			Self::True => write!(formatter, "true"),
 		}
 	}
@@ -148,8 +152,10 @@ pub(crate) fn is_keyword(identifier: &str) -> bool
 		| "exists"
 		| "false"
 		| "forall"
+		| "inf"
 		| "not"
 		| "or"
+		| "sup"
 		| "true" => true,
 		_ => false,
 	}
@@ -467,7 +473,6 @@ where
 					};
 
 					let input_left = self.original_input[self.previous_index..index_left].trim();
-					assert!(!input_left.is_empty());
 
 					self.previous_index = index_right;