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+title = "Forest evaluable not needed in the end"
+date = "2023-02-14"
+author = "Yann Herklotz"
+tags = []
+categories = []
+backlinks = ["3c3f5"]
+forwardlinks = ["3c3f7", "3c3f6a"]
+zettelid = "3c3f6"
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+
+At first I had a definition of `forest_evaluable` which said that the
+whole tree of predicate expressions could always be evaluated. However,
+in addition to that I had strict semantics of predicates, which is why
+to evaluate a predicate I had to know that I could evaluate both sides
+of the predicate before actually giving it a value. There were two
+problems:
+
+1.  With the strict evaluation of predicates, the evaluability of the
+    predicates was actually not right, because there were some cases
+    where the predicates would not be evaluable by design. For example,
+    when we have a predicate assignment that itself is gated:
+    `if (p) p2 = c`. In this case, when the predicate `p` evaluates to
+    `false`, then one cannot know if the condition `c` can be evaluated.
+    This means that one cannot actually evaluate the predicate
+    $p \implies p_2 := c$. Strict semantics dictate that one has to be
+    able to get a value for $p_2 := c$ though.
+2.  Many problems go away when one does not have strict evaluation
+    anymore, because one will always be able to evaluate on of the
+    predicates and therefore know the result of predicate. This also
+    solves the previous problem, which is actually quite subtle, that
+    when a predicate is maybe not evaluable, it is hidden behind an
+    implication.