Changes between Version 104 and Version 105 of TypeFunctionsSolving
 Timestamp:
 Apr 21, 2009 3:41:40 AM (7 years ago)
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TypeFunctionsSolving
v104 v105 255 255 * '''Step A:''' For any (local or wanted) variable equality of the form `co :: x ~ t`, we apply the substitution `[t/x]` to the '''righthand side''' of all equalities (wanteds only to wanteds). We also perform the same substitution on class constraints (again, wanteds only to wanteds). 256 256 * '''Step B:''' We have two cases: 257 * ''In checking mode,'' for any wanted family equality of the form `co :: F t1..tn ~ alpha`, we apply the substitution `[F t1..tn/alpha]` to '''both sides''' of all wanted variable and family equalities with the exception that, if `alpha` is a local flexible (introduced during flattening of wanteds), we do '''not''' substitute into family equalities of the form `co' :: G s1..sm ~ delta`, where `delta` is a nonlocal flexible.257 * ''In checking mode,'' for any wanted family equality of the form `co :: F t1..tn ~ alpha`, we apply the substitution `[F t1..tn/alpha]` to the righthand side of all wanted variable equalities and to both sides of all wanted family equalities with the exception that, if `alpha` is a local flexible (introduced during flattening of wanteds), we do '''not''' substitute into family equalities of the form `co' :: G s1..sm ~ delta`, where `delta` is a nonlocal flexible. 258 258 * ''In inference mode,'' we proceed as in checking mode, but we do not substitute into variable equalities. 259 259 2. '''Instantiation:''' For any variable equality of the form `co :: alpha ~ t` or `co :: a ~ alpha`, where `co` is wanted, we instantiate `alpha` with `t` or `a`, respectively, and set `co := id`. Moreover, we have to do the same for equalities of the form `co :: F t1..tn ~ alpha` unless we are in inference mode and `alpha` appears in the environment or any other wanteds. (We never instantiate any flexibles introduced by flattening locals.) '''!!!FIXME: Take the escaped locals into account!!!'''