lambda_hnf_capture.chr

:- module(lambda_hnf_capture, [result/2, fun adder_from_pair/1, type(tags/0)]).
:- chr_constraint result/2.
:- chr_type tags ---> pair(any, any) ; test1.
:- function adder_from_pair/1.

% adder_from_pair(pair(A, _)) takes a compound argument whose first
% field is extracted into A by an HNF-generated GuardGetArg guard. The
% RHS is a closure that captures A. This exercises the liftEquation
% scope fix: before the fix, A was not visible to the lambda-lifter
% (eq.params only contained the top-level _hnf_0), so the closure was
% lifted without capturing A and the reference dangled at runtime.
adder_from_pair(pair(A, _)) -> fun(X) -> X + A end.

result(test1, R) <=> F is adder_from_pair(pair(10, 99)), R is '$call'(F, 5).