%token CONST
%token VAR
%token IMP
%token FUN
%token LPAREN
%token RPAREN
%token APP

%nonassoc FUN
%nonassoc VAR CONST LPAREN
%left APP

%%

expr: CONST { my $litval = $_[1]; sub { $litval } }
    | VAR { my $varname = $_[1]; sub { my %args_ = @_; $args_{$varname} } }
    | FUN VAR IMP expr { my ($param, $term) = ($_[2], $_[4]); sub { my %args = @_; sub { $args{$param} = shift; $term->(%args) } } }
    | LPAREN expr RPAREN { $_[2] }
    | expr expr %prec APP { my ($op, $arg) = ($_[1], $_[2]); sub { my %args_ = @_; $op->(%args_)->($arg->(%args_)) } }
;

%%