Join points

This major patch implements Join Points, as described in
https://ghc.haskell.org/trac/ghc/wiki/SequentCore.  You have
to read that page, and especially the paper it links to, to
understand what's going on; but it is very cool.

It's Luke Maurer's work, but done in close collaboration with Simon PJ.

This Phab is a squash-merge of wip/join-points branch of
http://github.com/lukemaurer/ghc. There are many, many interdependent
changes.

Reviewers: goldfire, mpickering, bgamari, simonmar, dfeuer, austin

Subscribers: simonpj, dfeuer, mpickering, Mikolaj, thomie

Differential Revision: https://phabricator.haskell.org/D2853

1 files changed, 13 insertions, 0 deletions

diff --git a/compiler/utils/Outputable.hs b/compiler/utils/Outputable.hs
index 7d79f93bb2..3f94a68413 100644
--- a/compiler/utils/Outputable.hs
+++ b/compiler/utils/Outputable.hs
@@ -944,6 +944,19 @@ class Outputable a => OutputableBndr a where
       -- prefix position of an application, thus   (f a b) or  ((+) x)
       -- or infix position,                 thus   (a `f` b) or  (x + y)
 
+   pprNonRecBndrKeyword, pprRecBndrKeyword :: a -> SDoc
+      -- Print which keyword introduces the binder in Core code. This should be
+      -- "let" or "letrec" for a value but "join" or "joinrec" for a join point.
+   pprNonRecBndrKeyword _ = text "let"
+   pprRecBndrKeyword    _ = text "letrec"
+
+   pprLamsOnLhs :: a -> Int
+      -- For a join point of join arity n, we want to print j = \x1 ... xn -> e
+      -- as "j x1 ... xn = e" to differentiate when a join point returns a
+      -- lambda (the first rendering looks like a nullary join point returning
+      -- an n-argument function).
+   pprLamsOnLhs _ = 0
+
 {-
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