feat: Allow any Expr at the top level of a Policy Expression

This will enable testing policy expressions with a plain `#t` or `#f` to force
success or failure, as well as permit a JSON Pointer at the top level.

hipcheck/src/policy_exprs/expr.rs

@@ -183,7 +183,7 @@ fn parse_function(input: Input<'_>) -> IResult<Input<'_>, Expr> {
 
 pub fn parse(input: &str) -> Result<Expr> {
 	let tokens = Tokens::new(input);
-	let mut parser = all_consuming(parse_function);
+	let mut parser = all_consuming(parse_expr);
 
 	match parser(tokens).finish() {
 		Ok((rest, expr)) if rest.is_empty() => Ok(expr),
@@ -238,6 +238,14 @@ mod tests {
 		Expr::Array(vals)
 	}
 
+	#[test]
+	fn parse_bool() {
+		let input = "#t";
+		let expected = boolean(true).into_expr();
+		let result = parse(input).unwrap();
+		assert_eq!(result, expected);
+	}
+
 	#[test]
 	fn parse_function() {
 		let input = "(add 2 3)";

hipcheck/src/policy_exprs/mod.rs

@@ -80,6 +80,14 @@ mod tests {
 	use super::*;
 	use test_log::test;
 
+	#[test]
+	fn run_bool() {
+		let program = "#t";
+		let context = Value::Null;
+		let is_true = Executor::std().run(program, &context).unwrap();
+		assert!(is_true);
+	}
+
 	#[test]
 	fn run_basic() {
 		let program = "(eq (add 1 2) 3)";