Is there a way to connect this to template-haskell or haskell-src-exts code? On Fri, May 6, 2016 at 4:40 PM, Edward Z. Yang wrote:

Thanks Simon, that has all the ingredients I need.

I wrote some more docs for the function: https://phabricator.haskell.org/D2180

Edward

Excerpts from Simon Peyton Jones's message of 2016-05-06 02:05:31 -0700:

...

You probably want a variant on TcDeriv.simplifyDeriv, shorn of its complex error reporting.

Simon

| -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of | Edward Z. Yang | Sent: 06 May 2016 00:21 | To: ghc-devs | Subject: Determining if an instance is provided by the environment | | Hello all, | | Suppose I have a ClsInst from typechecking the following instance | declaration: | | instance Show [Char] -- i.e. String | | I'd now like to answer the question: "Is this instance 'provided' | by the instance environment?" For example, this instance is provided | given that I have these two instances in the environment: | | instance Show a => Show [a] -- (1) | instance Show Char -- (2) | | However, if I have just instance (1) in the environment, it's not | provided (and if you tried to use show "foo", you'd get the error that | Char is not an instance of Show.) | | Is there are convenient way to do this from TcM? With 'tcMatchTys' | and I can easily test if there is some instance in the environment | which *matches* my instance head (e.g., Show [a] matches Show [Char]) | but this doesn't tell me if all the resulting constraints are solvable. | | Thanks, | Edward | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail.ha | skell.org%2fcgi-bin%2fmailman%2flistinfo%2fghc- | devs&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com %7c8c304d9b355244c6 | ee7208d3753be740%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=iWdrnb6hC | 8pexyVkWNG22G%2fgdO10tCBy8nuCxhnO0M8%3d

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| I think I need to pass in a 'CtGiven' for 'Show a'. However, I don't | know what to pass as the evidence to the 'CtGiven' | constraints. My guess is that it doesn't matter? Correct, since you just want a yes/no answer. Just make up some fresh Ids with newEvVar. Simon | -----Original Message----- | From: Edward Z. Yang [mailto:ezyang@mit.edu] | Sent: 07 May 2016 01:34 | To: David Fox | Cc: Simon Peyton Jones ; ghc-devs | Subject: Re: Determining if an instance is provided by the environment | | Well, I have to write the new variant of this function :) | | Simon, I ran into a minor complication: if my instance is something | like: | | instance Show a => Show [a] | | I think I need to pass in a 'CtGiven' for 'Show a'. However, I don't | know what to pass as the evidence to the 'CtGiven' | constraints. My guess is that it doesn't matter? | | Edward | | Excerpts from David Fox's message of 2016-05-06 17:06:41 -0700: | > Is there a way to connect this to template-haskell or haskell-src- | exts code? | > | > On Fri, May 6, 2016 at 4:40 PM, Edward Z. Yang | wrote: | > | > > Thanks Simon, that has all the ingredients I need. | > > | > > I wrote some more docs for the function: | > > https://phabricator.haskell.org/D2180 | > > | > > Edward | > > | > > Excerpts from Simon Peyton Jones's message of 2016-05-06 02:05:31 - | 0700: | > > > You probably want a variant on TcDeriv.simplifyDeriv, shorn of | its | > > complex error reporting. | > > > | > > > Simon | > > > | > > > | -----Original Message----- | > > > | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf | > > > | Of Edward Z. Yang | > > > | Sent: 06 May 2016 00:21 | > > > | To: ghc-devs | > > > | Subject: Determining if an instance is provided by the | > > > | environment | > > > | | > > > | Hello all, | > > > | | > > > | Suppose I have a ClsInst from typechecking the following | > > > | instance | > > > | declaration: | > > > | | > > > | instance Show [Char] -- i.e. String | > > > | | > > > | I'd now like to answer the question: "Is this instance | 'provided' | > > > | by the instance environment?" For example, this instance is | > > > | provided given that I have these two instances in the | environment: | > > > | | > > > | instance Show a => Show [a] -- (1) | > > > | instance Show Char -- (2) | > > > | | > > > | However, if I have just instance (1) in the environment, it's | > > > | not provided (and if you tried to use show "foo", you'd get | the | > > > | error that Char is not an instance of Show.) | > > > | | > > > | Is there are convenient way to do this from TcM? With | 'tcMatchTys' | > > > | and I can easily test if there is some instance in the | > > > | environment which *matches* my instance head (e.g., Show [a] | > > > | matches Show [Char]) but this doesn't tell me if all the | > > > | resulting constraints are | > > solvable. | > > > | | > > > | Thanks, | > > > | Edward | > > > | _______________________________________________ | > > > | ghc-devs mailing list | > > > | ghc-devs@haskell.org | > > > | | > > | https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail | > > .ha | > > > | skell.org%2fcgi-bin%2fmailman%2flistinfo%2fghc- | > > > | devs&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com | > > %7c8c304d9b355244c6 | > > > | | > > | ee7208d3753be740%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=iWdrnb | > > 6hC | > > > | 8pexyVkWNG22G%2fgdO10tCBy8nuCxhnO0M8%3d | > > _______________________________________________ | > > ghc-devs mailing list | > > ghc-devs@haskell.org | > > | https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail | > > .haskell.org%2fcgi-bin%2fmailman%2flistinfo%2fghc- | devs&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7c7183659043984718 | 62ec08d3760f3aa2%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=LU%2fYHTo | y3Y4lSkMdJZD4PrHyAvuWiMOOg0Xm9RE5OTg%3d | > >