fn expr(&mut self) -> WeldResult<Box<Expr>> {
        if *self.peek() == TLet {
            self.let_expr()
        } else if *self.peek() == TBar || *self.peek() == TLogicalOr {
            self.lambda_expr()
        } else {
            self.operator_expr()
        }
    }
Parse an expression starting at the current position.
weld/src/syntax/parser.rs