Qualified names in TH?
I'm trying to write some Template Haskell code that (among other things) manipulates IntSets. So, for example, I'd like a splice to generate a call to Data.IntSet.fromList. However, I'm not sure how IntSet will be imported in the target module. Is there a way to resolve the fully qualified name (or similar) to a TH Name, without having to know how it's imported in the splicing module? (The obvious approach---mkName "Data.IntSet.fromList"---seems not to work in GHC 7.8.) Thanks! /g -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.
Using {-# LANGUAGE TemplateHaskell #-} you can use 'foo and ''Foo to get
access to the names in scope in the module that is building the splice,
rather than worrying about what names are in scope in the module the code
gets spliced into.
-Edward
On Mon, Mar 16, 2015 at 10:54 PM, J. Garrett Morris wrote: I'm trying to write some Template Haskell code that (among other
things) manipulates IntSets. So, for example, I'd like a splice to
generate a call to Data.IntSet.fromList. However, I'm not sure how
IntSet will be imported in the target module. Is there a way to
resolve the fully qualified name (or similar) to a TH Name, without
having to know how it's imported in the splicing module? (The obvious
approach---mkName "Data.IntSet.fromList"---seems not to work in GHC
7.8.) Thanks! /g --
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336. _______________________________________________
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What Edward says also applies to code quotations. So, for example:
module M
import IntSet
f :: Q Exp -> Q Exp
f blah = [| fromList $blah |]
module N where
import M
h x = $(f [| [x,x] |])
The splice expands to (fromList [x,x]), but the fromList guaranteed to be the fromList in scope where f is defined (in M), and NOT whatever other fromList might be in scope at the splice site in N.
Moreover, you do not need to import IntSet.
I hope that helps. Would someone like to add a section to https://wiki.haskell.org/Template_Haskell, to explain? There are several tutorials there as well.
Simon
From: Glasgow-haskell-users [mailto:glasgow-haskell-users-bounces@haskell.org] On Behalf Of Edward Kmett
Sent: 17 March 2015 05:01
To: J. Garrett Morris
Cc: GHC users
Subject: Re: Qualified names in TH?
Using {-# LANGUAGE TemplateHaskell #-} you can use 'foo and ''Foo to get access to the names in scope in the module that is building the splice, rather than worrying about what names are in scope in the module the code gets spliced into.
-Edward
On Mon, Mar 16, 2015 at 10:54 PM, J. Garrett Morris
participants (3)
-
Edward Kmett -
J. Garrett Morris -
Simon Peyton Jones