Changes between Version 87 and Version 88 of TypeFunctionsSolving
 Timestamp:
 Sep 7, 2008 9:10:55 AM (8 years ago)
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TypeFunctionsSolving
v87 v88 240 240 241 241 The finalisation step instantiates as many flexible type variables as possible, but it takes care not to instantiate variables occurring in the global environment with types containing synonym family applications. This is important to obtain principle types (c.f., Andrew Kennedy's thesis). We perform finalisation in two phases: 242 1. '''Substitution:''' For any variable equality of the form `co :: x ~ t` (both local and wanted), we apply the substitution `[t/x]` to all equalities.242 1. '''Substitution:''' For any variable equality of the form `co :: x ~ t` (both local and wanted), we apply the substitution `[t/x]` to the '''lefthand side''' of all equalities. 243 243 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`. 244 The substitution step can lead to recursive equalities; i.e., we need to apply an occurs check .244 The substitution step can lead to recursive equalities; i.e., we need to apply an occurs check after each substitution. It is an important property of propagation that we only need to substitute into righthand sides during finalisation. 245 245 246 246 == Examples ==