MODULE ::= EXPR*
EXPR ::=
  bool
| int
| ident
| VARDECL
| FUNCALL
| LAMBDA
VARDECL ::= opar decl ident EXPR cpar
FUNCALL ::= opar EXPR EXPR* cpar
LAMBDA ::= opar lambda opar PARAMS cpar BODY cpar
PARAMS ::= ident*
BODY ::= EXPR*