PROG ::= FUNCALL*
EXPR ::=
LITERAL
| FUNCALL
| VARDECL
| LAMBDA
LAMBDA ::= opar rarrow opar PARAMS cpar BODY cpar
PARAMS ::= ident*
BODY ::= expr*
VARDECL ::= opar decl ident EXPR cpar
FUNCALL ::= opar ident EXPR* cpar
LITERAL ::= int | ident