1 files changed, 343 insertions, 0 deletions
diff --git a/src/ast.rs b/src/ast.rs
new file mode 100644
index 0000000..5584975
--- /dev/null
+++ b/src/ast.rs
@@ -0,0 +1,343 @@
+use std::iter::Peekable;
+use std::sync::Arc;
+
+use rust_decimal::Decimal;
+
+use crate::tokens::{Lexer, Token};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Program {
+	pub commands: Arc<[Command]>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Command {
+	Statement(Statement),
+	Expression(Expression),
+	PanicMode(Arc<[Token]>),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Statement {
+	pub function_name: Arc<str>,
+	pub function_token: Token,
+	pub args: Arc<[Expression]>,
+	pub newline: Option<Token>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Expression {
+	pub prefix: Arc<[Token]>,
+	pub suffix: ExpressionSuffix,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ExpressionSuffix {
+	Nothing,
+	Number { value: Decimal, token: Token },
+	String { value: Arc<str>, token: Token },
+	Identifier { name: Arc<str>, token: Token },
+	List(List),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct List {
+	pub left_paren: Token,
+	pub items: Arc<[ListItem]>,
+	pub right_paren: Option<Token>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ListItem {
+	Dot(Token),
+	Expression(Expression),
+}
+
+impl Command {
+	pub fn is_empty(&self) -> bool {
+		if let Self::PanicMode(tokens) = self {
+			tokens.is_empty()
+		} else {
+			false
+		}
+	}
+
+	pub fn expression(&self) -> Option<&Expression> {
+		if let Self::Expression(expr) = self {
+			Some(expr)
+		} else {
+			None
+		}
+	}
+
+	pub fn statement(&self) -> Option<&Statement> {
+		if let Self::Statement(statement) = self {
+			Some(statement)
+		} else {
+			None
+		}
+	}
+}
+
+impl Expression {
+	pub fn is_quoted(&self) -> bool {
+		self.prefix.len() == 1 && self.prefix[0].is_apostrophe()
+	}
+}
+
+impl ExpressionSuffix {
+	pub fn is_empty(&self) -> bool {
+		matches!(self, Self::Nothing)
+	}
+
+	pub fn number(&self) -> Option<&Decimal> {
+		if let Self::Number { value, .. } = self {
+			Some(value)
+		} else {
+			None
+		}
+	}
+
+	pub fn string(&self) -> Option<&Arc<str>> {
+		if let Self::String { value, .. } = self {
+			Some(value)
+		} else {
+			None
+		}
+	}
+
+	pub fn identifier(&self) -> Option<&Arc<str>> {
+		if let Self::Identifier { name, .. } = self {
+			Some(name)
+		} else {
+			None
+		}
+	}
+
+	pub fn list(&self) -> Option<&List> {
+		if let Self::List(list) = self {
+			Some(list)
+		} else {
+			None
+		}
+	}
+}
+
+impl List {
+	pub fn contains_dot(&self) -> bool {
+		self.items.iter().any(|item| item.dot().is_some())
+	}
+}
+
+impl ListItem {
+	pub fn dot(&self) -> Option<&Token> {
+		if let Self::Dot(token) = self {
+			Some(token)
+		} else {
+			None
+		}
+	}
+
+	pub fn expression(&self) -> Option<&Expression> {
+		if let Self::Expression(expression) = self {
+			Some(expression)
+		} else {
+			None
+		}
+	}
+}
+
+fn parse_many<R>(
+	lexer: &mut Peekable<Lexer>,
+	predicate: fn(&Token) -> bool,
+	parser: fn(&mut Peekable<Lexer>) -> Result<R, String>,
+) -> Result<Vec<R>, String> {
+	let mut items = Vec::new();
+	while let Some(next) = lexer.peek() {
+		if !predicate(next) {
+			break;
+		}
+
+		items.push(parser(lexer)?)
+	}
+
+	Ok(items)
+}
+
+fn parse_if<R>(
+	lexer: &mut Peekable<Lexer>,
+	predicate: fn(&Token) -> bool,
+	parser: fn(&mut Peekable<Lexer>) -> Result<R, String>,
+) -> Option<Result<R, String>> {
+	let next = lexer.peek()?;
+	predicate(next).then(|| parser(lexer))
+}
+
+fn skip_whitespace_and_comments(lexer: &mut Peekable<Lexer>) {
+	while lexer
+		.next_if(|token| token.is_comment() || token.is_whitespace())
+		.is_some()
+	{}
+}
+
+fn skip_spaces_and_comments(lexer: &mut Peekable<Lexer>) {
+	while lexer
+		.next_if(|token: &Token| {
+			(token.is_whitespace() && !token.contains_newline()) || token.is_comment()
+		})
+		.is_some()
+	{}
+}
+
+fn skip_non_expression_tokens(lexer: &mut Peekable<Lexer>) -> Vec<Token> {
+	let mut tokens = Vec::new();
+	while let Some(token) = lexer.next_if(|token| !begins_expression(token)) {
+		tokens.push(token);
+	}
+
+	tokens
+}
+
+fn begins_expression(token: &Token) -> bool {
+	match &token.ty {
+		crate::tokens::TokenType::Whitespace(_) => false,
+		crate::tokens::TokenType::LineComment(_) => false,
+		crate::tokens::TokenType::BlockComment { .. } => false,
+		crate::tokens::TokenType::LeftParenthesis => true,
+		crate::tokens::TokenType::RightParenthesis => false,
+		crate::tokens::TokenType::Apostrophe => true,
+		crate::tokens::TokenType::Pound => true,
+		crate::tokens::TokenType::Dot => false,
+		crate::tokens::TokenType::Identifier(_) => true,
+		crate::tokens::TokenType::String { .. } => true,
+		crate::tokens::TokenType::Number(_) => true,
+	}
+}
+
+fn begins_list_item(token: &Token) -> bool {
+	begins_expression(token) || token.is_dot()
+}
+
+pub fn parse_program(lexer: &mut Peekable<Lexer>) -> Result<Program, String> {
+	skip_whitespace_and_comments(lexer);
+	let mut commands = parse_many(lexer, |_| true, parse_command)?;
+	if commands.last().map(|c| c.is_empty()).unwrap_or(false) {
+		commands.pop();
+	}
+
+	let commands = commands.into();
+	Ok(Program { commands })
+}
+
+fn parse_command(lexer: &mut Peekable<Lexer>) -> Result<Command, String> {
+	skip_whitespace_and_comments(lexer);
+	if let Some(result) = parse_if(lexer, |token| token.is_identifier(), parse_statement) {
+		result.map(Command::Statement)
+	} else if let Some(result) = parse_if(lexer, begins_expression, parse_expression) {
+		result.map(Command::Expression)
+	} else {
+		Ok(Command::PanicMode(skip_non_expression_tokens(lexer).into()))
+	}
+}
+
+fn parse_statement(lexer: &mut Peekable<Lexer>) -> Result<Statement, String> {
+	skip_whitespace_and_comments(lexer);
+	let function_token = lexer
+		.next()
+		.ok_or_else(|| String::from("expected a function name"))?;
+	let function_name = function_token
+		.identifier()
+		.ok_or_else(|| String::from("expected the function name to be an identifier"))?
+		.into();
+	skip_spaces_and_comments(lexer);
+	let args = parse_many(lexer, begins_expression, parse_expression)?.into();
+	skip_spaces_and_comments(lexer);
+	let newline = lexer.next_if(|token| token.contains_newline());
+
+	Ok(Statement {
+		function_name,
+		function_token,
+		args,
+		newline,
+	})
+}
+
+fn parse_expression(lexer: &mut Peekable<Lexer>) -> Result<Expression, String> {
+	skip_whitespace_and_comments(lexer);
+	let prefix = parse_many(
+		lexer,
+		|token| token.is_pound() || token.is_apostrophe(),
+		|parser| {
+			let result = parser.next().ok_or(String::new());
+			skip_whitespace_and_comments(parser);
+			result
+		},
+	)?
+	.into();
+	skip_whitespace_and_comments(lexer);
+	let suffix = parse_expression_suffix(lexer)?;
+	skip_spaces_and_comments(lexer);
+
+	Ok(Expression { prefix, suffix })
+}
+
+fn parse_expression_suffix(lexer: &mut Peekable<Lexer>) -> Result<ExpressionSuffix, String> {
+	skip_whitespace_and_comments(lexer);
+	if let Some(list) = parse_if(lexer, |token| token.is_left_parenthesis(), parse_list) {
+		list.map(ExpressionSuffix::List)
+	} else if let Some(identifier) = lexer.next_if(|token| token.is_identifier()) {
+		Ok(ExpressionSuffix::Identifier {
+			name: identifier
+				.identifier()
+				.ok_or_else(|| String::from("we just checked for an identifier"))?
+				.into(),
+			token: identifier,
+		})
+	} else if let Some(string) = lexer.next_if(|token| token.is_string()) {
+		Ok(ExpressionSuffix::String {
+			value: string
+				.computed_string()
+				.ok_or_else(|| String::from("we just checked for an string"))?
+				.into(),
+			token: string,
+		})
+	} else if let Some(number) = lexer.next_if(|token| token.is_number()) {
+		Ok(ExpressionSuffix::Number {
+			value: *number
+				.number()
+				.ok_or_else(|| String::from("we just checked for a number"))?,
+			token: number,
+		})
+	} else {
+		Ok(ExpressionSuffix::Nothing)
+	}
+}
+
+fn parse_list(lexer: &mut Peekable<Lexer>) -> Result<List, String> {
+	skip_whitespace_and_comments(lexer);
+	let left_paren = lexer
+		.next_if(|token| token.is_left_parenthesis())
+		.ok_or_else(|| String::from("Unexpected token. Expected a left parenthesis"))?;
+	skip_whitespace_and_comments(lexer);
+	let items = parse_many(lexer, begins_list_item, parse_list_item)?.into();
+	skip_whitespace_and_comments(lexer);
+	let right_paren = lexer.next_if(|token| token.is_right_parenthesis());
+
+	Ok(List {
+		left_paren,
+		items,
+		right_paren,
+	})
+}
+
+fn parse_list_item(lexer: &mut Peekable<Lexer>) -> Result<ListItem, String> {
+	skip_whitespace_and_comments(lexer);
+	if let Some(dot) = lexer.next_if(|token| token.is_dot()) {
+		skip_whitespace_and_comments(lexer);
+		Ok(ListItem::Dot(dot))
+	} else {
+		let result = parse_expression(lexer).map(ListItem::Expression);
+		skip_whitespace_and_comments(lexer);
+		result
+	}
+}