Now, only `(<- ...)`s occurring in the condition of a pure if-then-else
are lifted.
That is, `if (<- foo) then ... else ...` is ok, but `if ... then (<-
foo) else ...` is not. See #3713closes#3713
This PR also adjusts this repo. Note that some of the `(<- ...)` were
harmless since they were just accessing some
read-only state.
