Implement string interpolation

debug/app.ona

@@ -1,9 +1,6 @@
 
-let wrench = "wrench"
+let tool = "wrench"
-
+var test_param = `monkey {tool} {2 + 1 - 1}`
-var test_param = "monkey {wrench}"
-
-test_param = "monkey"
 
 let printer = lambda (pfx):
 	@print(test_param)

source/ona/kym.zig

@@ -133,6 +133,80 @@ pub const RuntimeEnv = struct {
 		};
 	}
 
+	pub fn concat(self: *RuntimeEnv, values: []const *const RuntimeRef) RuntimeError!*RuntimeRef {
+		if (values.len == 0) {
+			return self.new_string("");
+		}
+
+		var remaining_value_count = values.len;
+
+		errdefer {
+			var poppable_value_count = values.len - remaining_value_count;
+
+			while (poppable_value_count != 0) {
+				poppable_value_count -= 1;
+
+				const popped_value = self.pop_local() catch unreachable;
+
+				coral.debug.assert(popped_value != null);
+				self.discard(popped_value.?);
+			}
+		}
+
+		var length = @as(usize, 0);
+
+		while (remaining_value_count != 0) {
+			remaining_value_count -= 1;
+
+			const value_string = try self.to_string(values[remaining_value_count]);
+
+			errdefer self.discard(value_string);
+
+			const string = value_string.as_string();
+
+			coral.debug.assert(string != null);
+
+			try self.locals.push_one(value_string);
+
+			length += string.?.len;
+		}
+
+		const buffer = try coral.io.allocate_many(self.allocator, length, @as(coral.io.Byte, 0));
+
+		errdefer self.allocator.deallocate(buffer);
+
+		var written = @as(usize, 0);
+
+		while (remaining_value_count != values.len) : (remaining_value_count += 1) {
+			const value_string = try self.pop_local();
+
+			coral.debug.assert(value_string != null);
+
+			defer self.discard(value_string.?);
+
+			const string = value_string.?.as_string();
+
+			coral.debug.assert(string != null);
+
+			coral.io.copy(buffer[written ..], string.?);
+
+			written += string.?.len;
+
+			coral.debug.assert(written <= length);
+		}
+
+		return RuntimeRef.allocate(self.allocator, .{
+			.ref_count = 1,
+
+			.payload = .{
+				.string = .{
+					.ptr = buffer.ptr,
+					.len = @intCast(buffer.len),
+				},
+			},
+		});
+	}
+
 	pub fn discard(self: *RuntimeEnv, value: *RuntimeRef) void {
 		var object = value.object();
 
@@ -573,8 +647,9 @@ pub const RuntimeEnv = struct {
 
 				if (callable.as_dynamic(Chunk.typeinfo)) |chunk_userdata| {
 					const chunk = @as(*Chunk, @ptrCast(@alignCast(chunk_userdata)));
+					const line = chunk.lines.values[chunk.cursor];
 
-					const chunk_name = try coral.utf8.alloc_formatted(self.allocator, "{name}@{line}", .{
+					const chunk_name = try coral.utf8.alloc_formatted(self.allocator, "{name}@{line_number}", .{
 						.name = get_name: {
 							const string = name.as_string();
 
@@ -583,7 +658,7 @@ pub const RuntimeEnv = struct {
 							break: get_name string.?;
 						},
 
-						.line = chunk.lines.values[chunk.cursor],
+						.line_number = line.number,
 					});
 
 					defer self.allocator.deallocate(chunk_name);
@@ -1013,6 +1088,8 @@ pub const Typeinfo = struct {
 };
 
 pub fn assert(env: *RuntimeEnv, condition: bool) RuntimeError!void {
+	coral.debug.assert(condition);
+
 	if (!condition) {
 		return env.raise(error.IllegalState, "assertion", .{});
 	}

source/ona/kym/Chunk.zig

@@ -1,7 +1,3 @@
-const Expr = @import("./Expr.zig");
-
-const Stmt = @import("./Stmt.zig");
-
 const app = @import("../app.zig");
 
 const coral = @import("coral");
@@ -10,6 +6,8 @@ const file = @import("../file.zig");
 
 const kym = @import("../kym.zig");
 
+const tokens = @import("./tokens.zig");
+
 const tree = @import("./tree.zig");
 
 name: *kym.RuntimeRef,
@@ -31,7 +29,7 @@ const Compiler = struct {
 	chunk: *Self,
 	env: *kym.RuntimeEnv,
 
-	fn compile_argument(self: *const Compiler, environment: *const tree.Environment, initial_argument: ?*const Expr) kym.RuntimeError!u8 {
+	fn compile_argument(self: *const Compiler, environment: *const tree.Environment, initial_argument: ?*const tree.Expr) kym.RuntimeError!u8 {
 		// TODO: Exceeding 255 arguments will make the VM crash.
 		var maybe_argument = initial_argument;
 		var argument_count = @as(u8, 0);
@@ -46,7 +44,7 @@ const Compiler = struct {
 		return argument_count;
 	}
 
-	fn compile_expression(self: *const Compiler, environment: *const tree.Environment, expression: *const Expr, name: ?[]const coral.io.Byte) kym.RuntimeError!void {
+	fn compile_expression(self: *const Compiler, environment: *const tree.Environment, expression: *const tree.Expr, name: ?[]const coral.io.Byte) kym.RuntimeError!void {
 		const number_format = coral.utf8.DecimalFormat{
 			.delimiter = "_",
 			.positive_prefix = .none,
@@ -75,6 +73,24 @@ const Compiler = struct {
 				try self.chunk.write(expression.line, .{.push_const = try self.declare_string(literal)});
 			},
 
+			.string_template => {
+				var current_expression = expression.next orelse {
+					return self.chunk.write(expression.line, .{.push_const = try self.declare_string("")});
+				};
+
+				var component_count = @as(u8, 0);
+
+				while (true) {
+					try self.compile_expression(environment, current_expression, null);
+
+					component_count += 1;
+
+					current_expression = current_expression.next orelse {
+						return self.chunk.write(expression.line, .{.push_concat = component_count});
+					};
+				}
+			},
+
 			.symbol_literal => |literal| {
 				try self.chunk.write(expression.line, .{.push_const = try self.declare_symbol(literal)});
 			},
@@ -256,7 +272,7 @@ const Compiler = struct {
 		}
 	}
 
-	fn compile_statement(self: *const Compiler, environment: *const tree.Environment, initial_statement: *const Stmt) kym.RuntimeError!*const Stmt {
+	fn compile_statement(self: *const Compiler, environment: *const tree.Environment, initial_statement: *const tree.Stmt) kym.RuntimeError!*const tree.Stmt {
 		var current_statement = initial_statement;
 
 		while (true) {
@@ -445,7 +461,7 @@ const Compiler = struct {
 
 const ConstList = coral.list.Stack(*kym.RuntimeRef);
 
-const LineList = coral.list.Stack(u32);
+const LineList = coral.list.Stack(tokens.Line);
 
 pub const Opcode = union (enum) {
 	ret,
@@ -459,6 +475,7 @@ pub const Opcode = union (enum) {
 	push_table: u32,
 	push_builtin: Builtin,
 	push_binding: u8,
+	push_concat: u8,
 	push_boxed,
 	set_local: u8,
 	get_dynamic,
@@ -540,6 +557,10 @@ pub fn dump(chunk: Self, env: *kym.RuntimeEnv) kym.RuntimeError!*kym.RuntimeRef
 				.binding = push_binding,
 			}),
 
+			.push_concat => |push_concat| coral.utf8.print_formatted(writer, "push concat ({count})\n", .{
+				.count = push_concat,
+			}),
+
 			.push_builtin => |push_builtin| coral.utf8.print_formatted(writer, "push builtin ({builtin})\n", .{
 				.builtin = switch (push_builtin) {
 					.import => "import",
@@ -670,6 +691,33 @@ pub fn execute(self: *Self, env: *kym.RuntimeEnv, frame: *const kym.Frame) kym.R
 				try env.locals.push_one(if (self.bindings[push_binding]) |value| value.acquire() else null);
 			},
 
+			.push_concat => |push_concat| {
+				const frame_locals = env.locals.values[frame.locals_top ..];
+
+				try kym.assert(env, push_concat <= frame_locals.len);
+
+				const concat_locals = frame_locals[(frame_locals.len - push_concat) .. frame_locals.len];
+
+				for (concat_locals) |value| {
+					_ = try env.expect(value);
+				}
+
+				const concatenated_value = try env.concat(@ptrCast(concat_locals));
+
+				errdefer env.discard(concatenated_value);
+
+				var to_pop = concat_locals.len;
+
+				while (to_pop != 0) : (to_pop -= 1) {
+					const popped = env.pop_local() catch unreachable;
+
+					coral.debug.assert(popped != null);
+					env.discard(popped.?);
+				}
+
+				try env.locals.push_one(concatenated_value);
+			},
+
 			.bind => |bind| {
 				const callable = try env.expect(try env.pop_local());
 
@@ -1071,7 +1119,7 @@ fn typeinfo_to_string(env: *kym.RuntimeEnv, userdata: []coral.io.Byte) coral.io.
 	return env.to_string(@as(*Self, @ptrCast(@alignCast(userdata))).name);
 }
 
-pub fn write(self: *Self, line: u32, opcode: Opcode) coral.io.AllocationError!void {
+pub fn write(self: *Self, line: tokens.Line, opcode: Opcode) coral.io.AllocationError!void {
 	try self.opcodes.push_one(opcode);
 	try self.lines.push_one(line);
 }

source/ona/kym/tokens.zig

@@ -1,5 +1,9 @@
 const coral = @import("coral");
 
+pub const Line = struct {
+	number: u32,
+};
+
 pub const Token = union(enum) {
 	end,
 	unknown: coral.io.Byte,
@@ -105,7 +109,7 @@ pub const Token = union(enum) {
 
 pub const Stream = struct {
 	source: []const coral.io.Byte,
-	lines_stepped: u32 = 1,
+	line: Line = .{.number = 1},
 	token: Token = .newline,
 
 	pub fn skip_newlines(self: *Stream) void {
@@ -136,7 +140,7 @@ pub const Stream = struct {
 				'\n' => {
 					cursor += 1;
 					self.token = .newline;
-					self.lines_stepped += 1;
+					self.line.number += 1;
 
 					return;
 				},

source/ona/kym/tree.zig

@@ -1,6 +1,6 @@
-const Expr = @import("./Expr.zig");
+pub const Expr = @import("./tree/Expr.zig");
 
-const Stmt = @import("./Stmt.zig");
+pub const Stmt = @import("./tree/Stmt.zig");
 
 const coral = @import("coral");
 
@@ -163,22 +163,22 @@ pub const Root = struct {
 
 	const MessageList = coral.list.Stack([]coral.io.Byte);
 
-	pub fn report_error(self: *Root, stream: *tokens.Stream, comptime format: []const u8, args: anytype) ParseError {
+	pub fn report_error(self: *Root, line: tokens.Line, comptime format: []const u8, args: anytype) ParseError {
 		const allocator = self.arena.as_allocator();
 
-		try self.error_messages.push_one(try coral.utf8.alloc_formatted(allocator, "{line}: {message}", .{
+		try self.error_messages.push_one(try coral.utf8.alloc_formatted(allocator, "{line_number}: {message}", .{
 			.message = try coral.utf8.alloc_formatted(allocator, format, args),
-			.line = stream.lines_stepped,
+			.line_number = line.number,
 		}));
 
 		return error.BadSyntax;
 	}
 
-	pub fn report_declare_error(self: *Root, stream: *tokens.Stream, identifier: []const coral.io.Byte, @"error": Environment.DeclareError) ParseError {
+	pub fn report_declare_error(self: *Root, line: tokens.Line, identifier: []const coral.io.Byte, @"error": Environment.DeclareError) ParseError {
 		return switch (@"error") {
 			error.OutOfMemory => error.OutOfMemory,
 
-			error.DeclarationExists => self.report_error(stream, "declaration `{identifier}` already exists", .{
+			error.DeclarationExists => self.report_error(line, "declaration `{identifier}` already exists", .{
 				.identifier = identifier,
 			}),
 		};

source/ona/kym/tree/Expr.zig

@@ -2,12 +2,12 @@ const Stmt = @import("./Stmt.zig");
 
 const coral = @import("coral");
 
-const tokens = @import("./tokens.zig");
+const tokens = @import("../tokens.zig");
 
-const tree = @import("./tree.zig");
+const tree = @import("../tree.zig");
 
 next: ?*const Self = null,
-line: u32,
+line: tokens.Line,
 
 kind: union (enum) {
 	nil_literal,
@@ -15,6 +15,7 @@ kind: union (enum) {
 	false_literal,
 	number_literal: []const coral.io.Byte,
 	string_literal: []const coral.io.Byte,
+	string_template,
 	symbol_literal: []const coral.io.Byte,
 	table_construct: TableConstruct,
 	key_value: KeyValue,
@@ -74,14 +75,14 @@ pub const BinaryOp = struct {
 						stream.step();
 
 						if (stream.token == .end) {
-							return root.report_error(stream, "expected other half of expression after `" ++ comptime token.text() ++ "`", .{});
+							return root.report_error(stream.line, "expected other half of expression after `" ++ comptime token.text() ++ "`", .{});
 						}
 
 						// TODO: Remove once Zig has fixed struct self-reassignment.
 						const unnecessary_temp = expression;
 
 						expression = try root.create_expr(.{
-							.line = stream.lines_stepped,
+							.line = stream.line,
 
 							.kind = .{
 								.binary_op = .{
@@ -155,6 +156,68 @@ pub const TableConstruct = struct {
 	entry: ?*const Self,
 };
 
+const TemplateToken = union (enum) {
+	invalid: []const coral.io.Byte,
+	literal: []const coral.io.Byte,
+	expression: []const coral.io.Byte,
+
+	fn extract(source: *[]const coral.io.Byte) ?TemplateToken {
+		var cursor = @as(usize, 0);
+
+		defer source.* = source.*[cursor ..];
+
+		while (cursor < source.len) {
+			switch (source.*[cursor]) {
+				'{' => {
+					cursor += 1;
+
+					while (true) : (cursor += 1) {
+						if (cursor == source.len) {
+							return .{.invalid = source.*[0 .. cursor]};
+						}
+
+						if (source.*[cursor] == '}') {
+							const token = TemplateToken{.expression = source.*[1 .. cursor]};
+
+							cursor += 1;
+
+							return token;
+						}
+					}
+				},
+
+				else => {
+					cursor += 1;
+
+					while (true) : (cursor += 1) {
+						if (cursor == source.len) {
+							return .{.literal = source.*[0 .. cursor]};
+						}
+
+						if (source.*[cursor] == '{') {
+							const cursor_next = cursor + 1;
+
+							if (cursor_next == source.len) {
+								return .{.invalid = source.*[0 .. cursor]};
+							}
+
+							if (source.*[cursor_next] == '{') {
+								cursor = cursor_next;
+
+								return .{.literal = source.*[0 .. cursor]};
+							}
+
+							return .{.literal = source.*[0 .. cursor]};
+						}
+					}
+				}
+			}
+		}
+
+		return null;
+	}
+};
+
 pub const UnaryOp = struct {
 	operand: *Self,
 	operation: Operation,
@@ -172,16 +235,16 @@ pub fn parse(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Enviro
 		stream.skip_newlines();
 
 		if (stream.token == .end) {
-			return root.report_error(stream, "expected assignment after `=`", .{});
+			return root.report_error(stream.line, "expected assignment after `=`", .{});
 		}
 
 		return root.create_expr(.{
-			.line = stream.lines_stepped,
+			.line = stream.line,
 
 			.kind = switch (expression.kind) {
 				.declaration_get => |declaration_get| convert: {
 					if (declaration_get.declaration.is.readonly) {
-						return root.report_error(stream, "readonly declarations cannot be re-assigned", .{});
+						return root.report_error(stream.line, "readonly declarations cannot be re-assigned", .{});
 					}
 
 					break: convert .{
@@ -208,7 +271,7 @@ pub fn parse(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Enviro
 					},
 				},
 
-				else => return root.report_error(stream, "expected local or field on left-hand side of expression", .{}),
+				else => return root.report_error(stream.line, "expected local or field on left-hand side of expression", .{}),
 			},
 		});
 	}
@@ -244,13 +307,13 @@ fn parse_factor(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Env
 				const unnecessary_temp = expression;
 
 				expression = try root.create_expr(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 
 					.kind = .{
 						.field_get = .{
 							.identifier = switch (stream.token) {
 								.identifier => |field_identifier| field_identifier,
-								else => return root.report_error(stream, "expected identifier after `.`", .{}),
+								else => return root.report_error(stream.line, "expected identifier after `.`", .{}),
 							},
 
 							.object = unnecessary_temp,
@@ -268,7 +331,7 @@ fn parse_factor(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Env
 				const unnecessary_temp = expression;
 
 				expression = try root.create_expr(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 
 					.kind = .{
 						.subscript_get = .{
@@ -279,14 +342,14 @@ fn parse_factor(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Env
 				});
 
 				if (stream.token != .symbol_bracket_right) {
-					return root.report_error(stream, "expected closing `]` on subscript", .{});
+					return root.report_error(stream.line, "expected closing `]` on subscript", .{});
 				}
 
 				stream.skip_newlines();
 			},
 
 			.symbol_paren_left => {
-				const lines_stepped = stream.lines_stepped;
+				const lines_stepped = stream.line;
 
 				stream.skip_newlines();
 
@@ -301,7 +364,7 @@ fn parse_factor(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Env
 						switch (stream.token) {
 							.symbol_comma => stream.skip_newlines(),
 							.symbol_paren_right => break,
-							else => return root.report_error(stream, "expected `,` or `)` after lambda argument", .{}),
+							else => return root.report_error(stream.line, "expected `,` or `)` after lambda argument", .{}),
 						}
 
 						const next_argument = try parse(root, stream, environment);
@@ -343,13 +406,13 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			const expression = try parse(root, stream, environment);
 
 			if (stream.token != .symbol_paren_right) {
-				return root.report_error(stream, "expected a closing `)` after expression", .{});
+				return root.report_error(stream.line, "expected a closing `)` after expression", .{});
 			}
 
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .{.group = expression},
 			});
 		},
@@ -358,7 +421,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .nil_literal,
 			});
 		},
@@ -367,7 +430,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .true_literal,
 			});
 		},
@@ -376,7 +439,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .false_literal,
 			});
 		},
@@ -385,7 +448,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .{.number_literal = value},
 			});
 		},
@@ -394,50 +457,58 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .{.string_literal = value},
 			});
 		},
 
+		.template_string => |value| {
+			const line = stream.line;
+
+			stream.skip_newlines();
+
+			return parse_template(root, value, line, environment);
+		},
+
 		.symbol_at => {
 			stream.step();
 
 			const identifier = switch (stream.token) {
 				.identifier => |identifier| identifier,
-				else => return root.report_error(stream, "expected identifier after `@`", .{}),
+				else => return root.report_error(stream.line, "expected identifier after `@`", .{}),
 			};
 
 			stream.skip_newlines();
 
 			if (coral.io.are_equal(identifier, "import")) {
 				return root.create_expr(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 					.kind = .import_builtin,
 				});
 			}
 
 			if (coral.io.are_equal(identifier, "print")) {
 				return root.create_expr(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 					.kind = .print_builtin,
 				});
 			}
 
 			if (coral.io.are_equal(identifier, "vec2")) {
 				return root.create_expr(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 					.kind = .vec2_builtin,
 				});
 			}
 
 			if (coral.io.are_equal(identifier, "vec3")) {
 				return root.create_expr(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 					.kind = .vec3_builtin,
 				});
 			}
 
-			return root.report_error(stream, "unexpected identifier after `@`", .{});
+			return root.report_error(stream.line, "unexpected identifier after `@`", .{});
 		},
 
 		.symbol_period => {
@@ -445,13 +516,13 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 
 			const identifier = switch (stream.token) {
 				.identifier => |identifier| identifier,
-				else => return root.report_error(stream, "expected identifier after `.`", .{}),
+				else => return root.report_error(stream.line, "expected identifier after `.`", .{}),
 			};
 
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .{.symbol_literal = identifier},
 			});
 		},
@@ -460,12 +531,12 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 
 				.kind = .{
 					.declaration_get = .{
 						.declaration = (try environment.resolve_declaration(identifier)) orelse {
-							return root.report_error(stream, "undefined identifier `{identifier}`", .{
+							return root.report_error(stream.line, "undefined identifier `{identifier}`", .{
 								.identifier = identifier,
 							});
 						}
@@ -478,7 +549,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			if (stream.token != .symbol_paren_left) {
-				return root.report_error(stream, "expected `(` after opening lambda block", .{});
+				return root.report_error(stream.line, "expected `(` after opening lambda block", .{});
 			}
 
 			stream.skip_newlines();
@@ -488,11 +559,11 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			while (stream.token != .symbol_paren_right) {
 				const identifier = switch (stream.token) {
 					.identifier => |identifier| identifier,
-					else => return root.report_error(stream, "expected identifier", .{}),
+					else => return root.report_error(stream.line, "expected identifier", .{}),
 				};
 
 				_ = lambda_environment.declare_argument(identifier) catch |declare_error| {
-					return root.report_declare_error(stream, identifier, declare_error);
+					return root.report_declare_error(stream.line, identifier, declare_error);
 				};
 
 				stream.skip_newlines();
@@ -500,14 +571,14 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 				switch (stream.token) {
 					.symbol_comma => stream.skip_newlines(),
 					.symbol_paren_right => break,
-					else => return root.report_error(stream, "expected `,` or `)` after identifier", .{}),
+					else => return root.report_error(stream.line, "expected `,` or `)` after identifier", .{}),
 				}
 			}
 
 			stream.skip_newlines();
 
 			if (stream.token != .symbol_colon) {
-				return root.report_error(stream, "expected `:` after closing `)` of lambda identifiers", .{});
+				return root.report_error(stream.line, "expected `:` after closing `)` of lambda identifiers", .{});
 			}
 
 			stream.skip_newlines();
@@ -529,7 +600,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .{.lambda_construct = .{.environment = lambda_environment}},
 			});
 		},
@@ -539,7 +610,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 
 			if (stream.token == .symbol_brace_right) {
 				return root.create_expr(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 					.kind = .{.table_construct = .{.entry = null}},
 				});
 			}
@@ -561,13 +632,13 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			}
 
 			if (stream.token != .symbol_brace_right) {
-				return root.report_error(stream, "expected closing `}` on table construct", .{});
+				return root.report_error(stream.line, "expected closing `}` on table construct", .{});
 			}
 
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .{.table_construct = .{.entry = first_entry}},
 			});
 		},
@@ -576,7 +647,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 
 				.kind = .{
 					.unary_op = .{
@@ -591,7 +662,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 
 				.kind = .{
 					.unary_op = .{
@@ -602,7 +673,7 @@ fn parse_operand(root: *tree.Root, stream: *tokens.Stream, environment: *tree.En
 			});
 		},
 
-		else => return root.report_error(stream, "unexpected token in expression", .{}),
+		else => return root.report_error(stream.line, "unexpected token in expression", .{}),
 	}
 }
 
@@ -613,26 +684,26 @@ fn parse_table_entry(root: *tree.Root, stream: *tokens.Stream, environment: *tre
 
 			const field = switch (stream.token) {
 				.identifier => |identifier| identifier,
-				else => return root.report_error(stream, "expected identifier in field symbol literal", .{}),
+				else => return root.report_error(stream.line, "expected identifier in field symbol literal", .{}),
 			};
 
 			stream.skip_newlines();
 
 			if (stream.token != .symbol_equals) {
-				return root.report_error(stream, "expected `=` after table symbol key", .{});
+				return root.report_error(stream.line, "expected `=` after table symbol key", .{});
 			}
 
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 
 				.kind = .{
 					.key_value = .{
 						.value = try parse(root, stream, environment),
 
 						.key = try root.create_expr(.{
-							.line = stream.lines_stepped,
+							.line = stream.line,
 							.kind = .{.symbol_literal = field},
 						}),
 					},
@@ -646,19 +717,19 @@ fn parse_table_entry(root: *tree.Root, stream: *tokens.Stream, environment: *tre
 			const key = try parse(root, stream, environment);
 
 			if (stream.token != .symbol_bracket_right)  {
-				return root.report_error(stream, "expected `]` after subscript index expression", .{});
+				return root.report_error(stream.line, "expected `]` after subscript index expression", .{});
 			}
 
 			stream.skip_newlines();
 
 			if (stream.token != .symbol_equals) {
-				return root.report_error(stream, "expected `=` after table expression key", .{});
+				return root.report_error(stream.line, "expected `=` after table expression key", .{});
 			}
 
 			stream.skip_newlines();
 
 			return root.create_expr(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 
 				.kind = .{
 					.key_value = .{
@@ -673,6 +744,45 @@ fn parse_table_entry(root: *tree.Root, stream: *tokens.Stream, environment: *tre
 	}
 }
 
+fn parse_template(root: *tree.Root, template: []const coral.io.Byte, line: tokens.Line, environment: *tree.Environment) tree.ParseError!*Self {
+	const expression_head = try root.create_expr(.{
+		.line = line,
+		.kind = .string_template,
+	});
+
+	var expression_tail = expression_head;
+	var source = template;
+
+	while (TemplateToken.extract(&source)) |token| {
+		const expression = try switch (token) {
+			.invalid => |invalid| root.report_error(line, "invalid template format: `{invalid}`", .{
+				.invalid = invalid,
+			}),
+
+			.literal => |literal| root.create_expr(.{
+				.line = line,
+				.kind = .{.string_literal = literal},
+			}),
+
+			.expression => |expression| create: {
+				var stream = tokens.Stream{
+					.source = expression,
+					.line = line,
+				};
+
+				stream.step();
+
+				break: create try parse(root, &stream, environment);
+			},
+		};
+
+		expression_tail.next = expression;
+		expression_tail = expression;
+	}
+
+	return expression_head;
+}
+
 const parse_term = BinaryOp.parser(parse_factor, &.{
 	.multiplication,
 	.divsion,

source/ona/kym/tree/Stmt.zig

@@ -2,12 +2,12 @@ const Expr = @import("./Expr.zig");
 
 const coral = @import("coral");
 
-const tokens = @import("./tokens.zig");
+const tokens = @import("../tokens.zig");
 
-const tree = @import("./tree.zig");
+const tree = @import("../tree.zig");
 
 next: ?*const Self = null,
-line: u32,
+line: tokens.Line,
 
 kind: union (enum) {
 	top_expression: *const Expr,
@@ -46,17 +46,17 @@ pub fn parse(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Enviro
 
 			if (stream.token != .end and stream.token != .newline) {
 				return root.create_stmt(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 					.kind = .{.@"return" = .{.returned_expression = try Expr.parse(root, stream, environment)}},
 				});
 			}
 
 			if (stream.token != .end and stream.token != .newline) {
-				return root.report_error(stream, "expected end or newline after return statement", .{});
+				return root.report_error(stream.line, "expected end or newline after return statement", .{});
 			}
 
 			return root.create_stmt(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 				.kind = .{.@"return" = .{.returned_expression = null}},
 			});
 		},
@@ -69,7 +69,7 @@ pub fn parse(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Enviro
 			const condition_expression = try Expr.parse(root, stream, environment);
 
 			if (stream.token != .symbol_colon) {
-				return root.report_error(stream, "expected `:` after `while` statement", .{});
+				return root.report_error(stream.line, "expected `:` after `while` statement", .{});
 			}
 
 			stream.skip_newlines();
@@ -88,7 +88,7 @@ pub fn parse(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Enviro
 			}
 
 			return root.create_stmt(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 
 				.kind = .{
 					.@"while" = .{
@@ -106,13 +106,13 @@ pub fn parse(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Enviro
 
 			const identifier = switch (stream.token) {
 				.identifier => |identifier| identifier,
-				else => return root.report_error(stream, "expected identifier after declaration", .{}),
+				else => return root.report_error(stream.line, "expected identifier after declaration", .{}),
 			};
 
 			stream.skip_newlines();
 
 			if (stream.token != .symbol_equals) {
-				return root.report_error(stream, "expected `=` after declaration `{identifier}`", .{
+				return root.report_error(stream.line, "expected `=` after declaration `{identifier}`", .{
 					.identifier = identifier,
 				});
 			}
@@ -120,7 +120,7 @@ pub fn parse(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Enviro
 			stream.skip_newlines();
 
 			return root.create_stmt(.{
-				.line = stream.lines_stepped,
+				.line = stream.line,
 
 				.kind = .{
 					.declare = .{
@@ -129,12 +129,12 @@ pub fn parse(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Enviro
 						.declaration = declare: {
 							if (is_constant) {
 								break: declare environment.declare_constant(identifier) catch |declaration_error| {
-									return root.report_declare_error(stream, identifier, declaration_error);
+									return root.report_declare_error(stream.line, identifier, declaration_error);
 								};
 							}
 
 							break: declare environment.declare_variable(identifier) catch |declaration_error| {
-								return root.report_declare_error(stream, identifier, declaration_error);
+								return root.report_declare_error(stream.line, identifier, declaration_error);
 							};
 						},
 					},
@@ -145,7 +145,7 @@ pub fn parse(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Enviro
 		.keyword_if => return parse_branch(root, stream, environment),
 
 		else => return root.create_stmt(.{
-			.line = stream.lines_stepped,
+			.line = stream.line,
 			.kind = .{.top_expression = try Expr.parse(root, stream, environment)},
 		}),
 	}
@@ -157,7 +157,7 @@ fn parse_branch(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Env
 	const expression = try Expr.parse(root, stream, environment);
 
 	if (stream.token != .symbol_colon) {
-		return root.report_error(stream, "expected `:` after `{token}`", .{.token = stream.token.text()});
+		return root.report_error(stream.line, "expected `:` after `{token}`", .{.token = stream.token.text()});
 	}
 
 	stream.skip_newlines();
@@ -171,7 +171,7 @@ fn parse_branch(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Env
 				stream.skip_newlines();
 
 				return root.create_stmt(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 
 					.kind = .{
 						.@"if" = .{
@@ -187,7 +187,7 @@ fn parse_branch(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Env
 				stream.step();
 
 				if (stream.token != .symbol_colon) {
-					return root.report_error(stream, "expected `:` after `if` statement condition", .{});
+					return root.report_error(stream.line, "expected `:` after `if` statement condition", .{});
 				}
 
 				stream.skip_newlines();
@@ -205,7 +205,7 @@ fn parse_branch(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Env
 				stream.skip_newlines();
 
 				return root.create_stmt(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 
 					.kind = .{
 						.@"if" = .{
@@ -219,7 +219,7 @@ fn parse_branch(root: *tree.Root, stream: *tokens.Stream, environment: *tree.Env
 
 			.keyword_elif => {
 				return root.create_stmt(.{
-					.line = stream.lines_stepped,
+					.line = stream.line,
 
 					.kind = .{
 						.@"if" = .{