appfreeexpr:
 | LET IDENT EQUAL expr IN expr { ExprLet($2, [], $4, $6) }

expr:
   exprapplist { match $1 with [x] -> x | x -> ExprApp x}

exprapplist:
   appfreeexpr { [$1] }
 | appfreeexpr exprapplist { $1 :: $2 }