--- At a variable occurrence, add in any free variables of its rule rhss
--- Curiously, we gather the Id's free *type* variables from its binding
--- site, but its free *rule-rhs* variables from its usage sites. This
--- is a little weird. The reason is that the former is more efficient,
--- but the latter is more fine grained, and a makes a difference when
--- a variable mentions itself one of its own rule RHSs
+-- Comment about obselete code
+-- We used to gather the free variables the RULES at a variable occurrence
+-- with the following cryptic comment:
+-- "At a variable occurrence, add in any free variables of its rule rhss
+-- Curiously, we gather the Id's free *type* variables from its binding
+-- site, but its free *rule-rhs* variables from its usage sites. This
+-- is a little weird. The reason is that the former is more efficient,
+-- but the latter is more fine grained, and a makes a difference when
+-- a variable mentions itself one of its own rule RHSs"
+-- Not only is this "weird", but it's also pretty bad because it can make
+-- a function seem more recursive than it is. Suppose
+-- f = ...g...
+-- g = ...
+-- RULE g x = ...f...
+-- Then f is not mentioned in its own RHS, and needn't be a loop breaker
+-- (though g may be). But if we collect the rule fvs from g's occurrence,
+-- it looks as if f mentions itself. (This bites in the eftInt/eftIntFB
+-- code in GHC.Enum.)
+--
+-- Anyway, it seems plain wrong. The RULE is like an extra RHS for the
+-- function, so its free variables belong at the definition site.
+--
+-- Deleted code looked like
+-- foldVarSet add_rule_var var_itself_set (idRuleVars var)
+-- add_rule_var var set | keep_it fv_cand in_scope var = extendVarSet set var
+-- | otherwise = set
+-- SLPJ Feb06
+