Changes between Version 104 and Version 105 of TypeFunctionsSolving


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Timestamp:
Apr 21, 2009 3:41:40 AM (6 years ago)
Author:
chak
Comment:

--

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  • TypeFunctionsSolving

    v104 v105  
    255255  * '''Step A:''' For any (local or wanted) variable equality of the form `co :: x ~ t`, we apply the substitution `[t/x]` to the '''right-hand side''' of all equalities (wanteds only to wanteds).  We also perform the same substitution on class constraints (again, wanteds only to wanteds). 
    256256  * '''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 non-local 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 right-hand 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 non-local flexible. 
    258258   * ''In inference mode,'' we proceed as in checking mode, but we do not substitute into variable equalities. 
    259259 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!!!'''