Trees that Grow in the hsSyn AST
Simon Peyton Jones
simonpj at microsoft.com
Thu May 25 22:48:47 UTC 2017
Do take a look at this:
· We propose to re-engineer HsSyn itself. This will touch a lot of code.
· But it’s very neat, and will bring big long-term advantages
· And we can do it a bit at a time
The wiki page https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow has the details.
It’s entirely an internal change, not a change to GHC’s specification, so it’s independent of the GHC proposals process. But I’d value the opinion of other GHC devs.
Alan has done a prototype first step, which worked out rather well. Rather than having
(which we all know means “HsExpr after the typechecker” but tha’s a bit inexplicit, we have
meaning “HsExpr after GHC’s Tc pass”. In some ways this is quite superficial, but it unlocks the Trees That Grow machiney.
Please ask questions etc. Alan and Shayan can record the answers in the wiki. I’m inclined to go ahead with this, so yell soon if you disagree.
From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Alan & Kim Zimmerman
Sent: 24 May 2017 22:52
To: ghc-devs at haskell.org
Subject: Trees that Grow in the hsSyn AST
You may be aware that Shayan Najd presented the paper "Trees that Grow" at HIW last year.
Based on the following mandate
> As in my previous email to Shayan (attached). Wiki page, describe goals, design,
> approach. Point to prototype implementation. Seek comments. You can say that
>I am supportive!
We have set up a Wiki page at  describing a prototype implementation of the first stage of this for the hsSyn AST, which is to change the polymorphic variable from one of RdrName / Name / Id to an index type. This is presented as a fabricator diff at .
Please take a look and provide feedback.
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