xnyhps / ghc Goto Github PK
View Code? Open in Web Editor NEWThis project forked from ghc/ghc
Mirror of ghc repository. DO NOT SUBMIT PULL REQUESTS HERE
Home Page: http://www.haskell.org/ghc/
License: Other
ghc's People
Contributors
Stargazers
Watchers
ghc's Issues
No -XNoMonomorphismRestriction: GHC.Prim.Any * types show up
Without -XNoMonomorphismRestriction, the type of the module:
f = _?h >>= _?gis found to be:
f :: GHC.Prim.Any (* -> *) (GHC.Prim.Any *)(Even when interpreting GHC.Prim.Any * as forall a. a, this is incorrect as the Monad constraint is not on the first * -> *)
With -XNoMonomorphismRestriction, the type is correctly:
f :: Monad m => m b-XNoMonomorphismRestriction: Holes aren't reported
Opening the following module with -XNoMonomorphismRestriction:
f = _?h >>= _?gCauses the holes to not be reported.
One of the differences in the log:
-XNoMonomorphismRestriction on:
solveWanteds finished with
remaining_unsolved_flats = {}
subst = [TvSubst In scope: InScope [] Type env: []]
simplifyCheck } unsolved = WC {}
Off:
solveWanteds finished with
remaining_unsolved_flats = {[W] $dMonad :: Monad
m_b {0} (CDictCan),
[W] _?h :: _?h (m_b a_c) {0} (CHoleCan),
[W] _?g :: _?g (a_c -> m_b b_d) {0} (CHoleCan)}
subst = [TvSubst In scope: InScope [] Type env: []]
simplifyCheck }
unsolved = WC {wc_flat = [W] $dMonad :: Monad m_b {0} (CDictCan)
[W] _?h :: _?h (m_b a_c) {0} (CHoleCan)
[W] _?g :: _?g (a_c -> m_b b_d) {0} (CHoleCan)}
-XNoMonomorphismRestriction: Named holes aren't shared
Probably directly a consequence of #1.
With -XNoMonomorphismRestriction the holes that are found (which are only visible in the debug messages from the constraint solver, because #1), don't share their type with the holes in other functions in the same module. For example:
f = _?h >>= _?g
g = [_?h, Just ()]Logs:
tcRnSrcDecls: WC {wc_impl = Implic {Untouchables = No untouchables
Skolems = []
Given = _?h :: _?h (Maybe ())
Wanted = WC {wc_flat = [W] _?h :: _?h
(Maybe
()) {0} (CNonCanonical)}
Binds = EvBindsVar<auS>
the inferred type of g :: (_?h (Maybe ())) => t_a
test.hs:3:1-18}
Implic {Untouchables = No untouchables
Skolems = [m, a, b]
Given = $dMonad :: Monad m_f
_?h :: _?h (m_f a_g)
_?g :: _?g (a_g -> m_f b_h)
Wanted = WC {wc_flat = [W] $dMonad :: Monad
m_f {0} (CNonCanonical)
[W] _?h :: _?h
(m_f a_g) {0} (CNonCanonical)
[W] _?g :: _?g
(a_g
-> m_f b_h) {0} (CNonCanonical)}
Binds = EvBindsVar<avb>
the inferred type of
f :: (Monad m_f, _?h (m_f a_g), _?g (a_g -> m_f b_h)) => t_e
test.hs:1:1-15}}
Without -XNoMonomorphismRestriction, the result is:
tcRnSrcDecls: WC {wc_flat = [W] _?h :: _?h
(Maybe ()) {0} (CNonCanonical)
[W] $dMonad :: Monad m_f {0} (CNonCanonical)
[W] _?h :: _?h (m_f a_g) {0} (CNonCanonical)
[W] _?g :: _?g (a_g -> m_f b_h) {0} (CNonCanonical)}
After that, _?h becomes shared (and this information propagates to _?g):
test.hs:1:13: Warning:
Found hole _?g with type () -> Maybe b0
In the second argument of `(>>=)', namely `_?g'
In the expression: _?h >>= _?g
In an equation for `f': f = _?h >>= _?g
test.hs:3:6: Warning:
Found hole _?h with type Maybe ()
In the expression: _?h
In the expression: [_?h, Just ()]
In an equation for `g': g = [_?h, Just ()]
Ok, modules loaded: Main.
-XNoMonomorphismRestriction: Show and IO leak to the type of the hole
With the following module:
f = _?hand -XNoMonomorphismRestriction on, running f gives:
<interactive>:4:1: Warning:
Found hole _?h with type Show a0 => IO a0
In a stmt of an interactive GHCi command: it <- f
<interactive>:4:1: Warning:
No instance for (Show a0) arising from a use of `print'
The type variable `a0' is ambiguous
Possible fix: add a type signature that fixes these type variable(s)
Note: there are several potential instances:
instance Show Double -- Defined in `GHC.Float'
instance Show Float -- Defined in `GHC.Float'
instance Show () -- Defined in `GHC.Show'
...plus 24 others
In a stmt of an interactive GHCi command: print it
*** Exception: <interactive>:4:1:
Found hole _?h with type Show a0 => IO a0
In a stmt of an interactive GHCi command: it <- f
(deferred type error)
In short, it shows the type of the hole to be Show a0 => IO a0, which is caused by the print it ghci calls internally to run the expression.
This is probably related to #1 and #3.
Recommend Projects
-
React
A declarative, efficient, and flexible JavaScript library for building user interfaces.
-
Vue.js
🖖 Vue.js is a progressive, incrementally-adoptable JavaScript framework for building UI on the web.
-
Typescript
TypeScript is a superset of JavaScript that compiles to clean JavaScript output.
-
TensorFlow
An Open Source Machine Learning Framework for Everyone
-
Django
The Web framework for perfectionists with deadlines.
-
Laravel
A PHP framework for web artisans
-
D3
Bring data to life with SVG, Canvas and HTML. 📊📈🎉
-
Recommend Topics
-
javascript
JavaScript (JS) is a lightweight interpreted programming language with first-class functions.
-
web
Some thing interesting about web. New door for the world.
-
server
A server is a program made to process requests and deliver data to clients.
-
Machine learning
Machine learning is a way of modeling and interpreting data that allows a piece of software to respond intelligently.
-
Visualization
Some thing interesting about visualization, use data art
-
Game
Some thing interesting about game, make everyone happy.
Recommend Org
-
Facebook
We are working to build community through open source technology. NB: members must have two-factor auth.
-
Microsoft
Open source projects and samples from Microsoft.
-
Google
Google ❤️ Open Source for everyone.
-
Alibaba
Alibaba Open Source for everyone
-
D3
Data-Driven Documents codes.
-
Tencent
China tencent open source team.