diff options
| author | Ryan Scott <ryan.gl.scott@gmail.com> | 2017-09-29 23:32:41 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2017-09-30 09:30:09 -0400 |
| commit | 626f0454ef1ca8f40c38064197dba97a36d52dbb (patch) | |
| tree | 66bdedc950adacd4651d7f70f995e29b400a79ac /libraries/template-haskell | |
| parent | 9c05fc4c31edde34a68317b45fdd71510d868f60 (diff) | |
| download | haskell-626f0454ef1ca8f40c38064197dba97a36d52dbb.tar.gz | |
Document a law for TH's Lift class
Inspired by the discussion in #14296, I've decided to
document a law which is usually in the back of my mind when I'm using
Template Haskell's `Lift` class, but isn't formally stated anywhere.
That is, every `Lift` instance should satisfy (for all `x`):
```lang=haskell
$(lift x) == x
```
Test Plan: Read it
Reviewers: austin, goldfire, bgamari
Subscribers: rwbarton, thomie
Differential Revision: https://phabricator.haskell.org/D4050
Diffstat (limited to 'libraries/template-haskell')
| -rw-r--r-- | libraries/template-haskell/Language/Haskell/TH/Syntax.hs | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/libraries/template-haskell/Language/Haskell/TH/Syntax.hs b/libraries/template-haskell/Language/Haskell/TH/Syntax.hs index 419d94480b..0541a088bf 100644 --- a/libraries/template-haskell/Language/Haskell/TH/Syntax.hs +++ b/libraries/template-haskell/Language/Haskell/TH/Syntax.hs @@ -565,6 +565,9 @@ sequenceQ = sequence -- Template Haskell has no way of knowing what value @x@ will take on at -- splice-time, so it requires the type of @x@ to be an instance of 'Lift'. -- +-- A 'Lift' instance must satisfy @$(lift x) ≡ x@ for all @x@, where @$(...)@ +-- is a Template Haskell splice. +-- -- 'Lift' instances can be derived automatically by use of the @-XDeriveLift@ -- GHC language extension: -- |