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don't say 'thing'

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Niko Matsakis 2018-03-09 04:19:36 -05:00
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src/traits-canonicalization.md
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@ -2,13 +2,15 @@
Canonicalization is the process of **isolating** an inference value
from its context. It is really based on a very simple concept: every
[inference variable](./type-inference.html#vars) is always in one of two
states: either it is **unbound**, in which case we don't know yet what
type it is, or it is **bound**, in which case we do. So to isolate
some thing T from its environment, we just walk down and find the
unbound variables that appear in T; those variables get renumbered in
a canonical order (left to right, for the most part, but really it
doesn't matter as long as it is consistent).
[inference variable](./type-inference.html#vars) is always in one of
two states: either it is **unbound**, in which case we don't know yet
what type it is, or it is **bound**, in which case we do. So to
isolate some data-structure T that contains types/regions from its
environment, we just walk down and find the unbound variables that
appear in T; those variables get replaced with "canonical variables",
starting from zero and numbered in a fixed order (left to right, for
the most part, but really it doesn't matter as long as it is
consistent).
So, for example, if we have the type `X = (?T, ?U)`, where `?T` and
`?U` are distinct, unbound inference variables, then the canonical