Refactor coercion holes
authorSimon Peyton Jones <simonpj@microsoft.com>
Thu, 21 Dec 2017 13:31:13 +0000 (13:31 +0000)
committerSimon Peyton Jones <simonpj@microsoft.com>
Thu, 21 Dec 2017 14:14:21 +0000 (14:14 +0000)
commita492af06d3264530d134584f22ffb726a16c78ec
tree294b0c21775d6a7cb9b79c86145d7b6ca47c81ea
parent72938f5890dac81afad52bf58175c1e29ffbc6dd
Refactor coercion holes

In fixing Trac #14584 I found that it would be /much/ more
convenient if a "hole" in a coercion (much like a unification
variable in a type) acutally had a CoVar associated with it
rather than just a Unique.  Then I can ask what the free variables
of a coercion is, and get a set of CoVars including those
as-yet-un-filled in holes.

Once that is done, it makes no sense to stuff coercion holes
inside UnivCo.  They were there before so we could know the
kind and role of a "hole" coercion, but once there is a CoVar
we can get that info from the CoVar.  So I removed HoleProv
from UnivCoProvenance and added HoleCo to Coercion.

In summary:

* Add HoleCo to Coercion and remove HoleProv from UnivCoProvanance

* Similarly in IfaceCoercion

* Make CoercionHole have a CoVar in it, not a Unique

* Make tyCoVarsOfCo return the free coercion-hole variables
  as well as the ordinary free CoVars.  Similarly, remember
  to zonk the CoVar in a CoercionHole

We could go further, and remove CoercionHole as a distinct type
altogther, just collapsing it into HoleCo.  But I have not done
that yet.
25 files changed:
compiler/backpack/RnModIface.hs
compiler/coreSyn/CoreFVs.hs
compiler/coreSyn/CoreLint.hs
compiler/iface/IfaceSyn.hs
compiler/iface/IfaceType.hs
compiler/iface/TcIface.hs
compiler/iface/ToIface.hs
compiler/typecheck/TcCanonical.hs
compiler/typecheck/TcEnv.hs
compiler/typecheck/TcErrors.hs
compiler/typecheck/TcHsSyn.hs
compiler/typecheck/TcInteract.hs
compiler/typecheck/TcMType.hs
compiler/typecheck/TcPluginM.hs
compiler/typecheck/TcRnTypes.hs
compiler/typecheck/TcSMonad.hs
compiler/typecheck/TcTyDecls.hs
compiler/typecheck/TcType.hs
compiler/typecheck/TcUnify.hs
compiler/typecheck/TcValidity.hs
compiler/types/Coercion.hs
compiler/types/FamInstEnv.hs
compiler/types/OptCoercion.hs
compiler/types/TyCoRep.hs
compiler/types/Type.hs