%if False

> module Let8
> where
> import MLexer2
>
> data Expr                     =   Const Int | Var String | Bin Expr Op Expr | Let Decl Expr
>                                   deriving (Show)
>
> data Decl                     =   String :=: Expr
>                                   deriving (Show)

%endif

> expr                          ::  Lex IO Expr

%if False

> %{
>
> Terminal                      =   Numeral {Int}
>                               |   Ident {String}
>                               |   Addop {Op}
>                               |   Mulop {Op}
>                               |   KWLet  as "let"
>                               |   KWIn   as "in"
>                               |   Equal  as "="
>                               |   LParen as "("
>                               |   RParen as ")"
>                               |   *EOF;
>
> left     6 Addop {Op};
> left     7 Mulop {Op};
> nonassoc 0 "in";

%endif

> expr  {Expr};
> expr  {Const n}               :   Numeral {n};
>       {Var s}                 |   Ident {s};
>       {Bin e1 op e2}          |   expr {e1}, Addop {op}, expr {e2};
>       {Bin e1 op e2}          |   expr {e1}, Mulop {op}, expr {e2};
>       {Let d e}               |   "let", decl {d}, "in", expr {e};
>       {e}                     |   "(", expr {e}, close {_};
>
> close  {()};
> close  {()}                   :   ")";
>        {% insert ")"}         |   insert ")";

%if False

> decl  {Decl};
> decl  {s :=: e}               :   Ident {s}, "=", expr {e};
>
> }%

%endif

> insert                        ::  String -> Lex IO ()
> insert s                      =   lift (putStrLn ("Warning: " ++ s ++ " inserted"))