Improve handling of `?`-variables #1933

Job	Run time
Stack / Unit Tests	1m 16s
Formatting and Style	20s
Nix / All Tests (self-hosted, linux, normal, Ubuntu-22.04, x86_64-linux)	1m 15s
Nix / All Tests (MacM1, self-macos-12, aarch64-darwin)	1m 15s
Nix / All Tests (macos-12, macos-12, x86_64-darwin)	57s
	5m 3s

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