[GHC] #8318: GHC does not infer type of `tagToEnum#` expression
#8318: GHC does not infer type of `tagToEnum#` expression ----------------------------+---------------------------------------------- Reporter: | Owner: jstolarek | Status: new Type: bug | Milestone: Priority: normal | Version: 7.7 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects valid program Architecture: | Test Case: Unknown/Multiple | Blocking: Difficulty: Unknown | Blocked By: | Related Tickets: | ----------------------------+---------------------------------------------- Compiling this program: {{{ {-# LANGUAGE MagicHash #-} module TTE where import GHC.Prim f = case tagToEnum# 1# of True -> "True" False -> "False" }}} gives a compilation error: {{{ [1 of 1] Compiling TTE ( tte.hs, tte.o ) tte.hs:6:10: tagToEnum# must appear applied to one argument In the expression: tagToEnum# 1# In the expression: case tagToEnum# 1# of { True -> "True" False -> "False" } In an equation for ‛f’: f = case tagToEnum# 1# of { True -> "True" False -> "False" } }}} To make it work one needs to supply type annotation for `tagToEnum#`: `case tagToEnum# 1# :: Bool of`. I would expect however that type will be inferred from type of patterns in the branches. Although I can imagine that things might get complicated for an ill-typed program: {{{ f = case tagToEnum# 1# of True -> "True" 3 -> "What now?" }}} If it is not possible to infer type of scrutinee based on patterns then I would expect to get more informative error message. Current one - `tagToEnum# must appear applied to one argument` - is very misleading. When I saw it for the first time it took me about 15 minutes to actually figure out what GHC expects me to do. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8318 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8318: GHC does not infer type of `tagToEnum#` expression ----------------------------------------------+---------------------------- Reporter: jstolarek | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by jstolarek): Compiling this program: {{{ {-# LANGUAGE MagicHash, UnboxedTuples #-} module TTE where import GHC.Prim import GHC.Base g :: IO Bool g = IO $ \s# -> (# s#, tagToEnum# 1# #) }}} produces: {{{ [1 of 1] Compiling TTE ( tte.hs, tte.o ) tte.hs:11:24: Bad call to tagToEnum# at type a_azp Specify the type by giving a type signature e.g. (tagToEnum# x) :: Bool In the expression: tagToEnum# 1# In the expression: (# s#, tagToEnum# 1# #) In the second argument of ‛($)’, namely ‛\ s# -> (# s#, tagToEnum# 1# #) }}} So the informative error message is already somewhere in the compiler. I wonder why don't we infer the type here? After all the error message clearly states what type is necessary. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8318#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8318: GHC does not infer type of `tagToEnum#` expression ----------------------------------------------+---------------------------- Reporter: jstolarek | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Changes (by parcs): * cc: patrick@… (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8318#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8318: GHC does not infer type of `tagToEnum#` expression
-------------------------------------+-------------------------------------
Reporter: jstolarek | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.7
(Type checker) | Keywords:
Resolution: | Architecture: Unknown/Multiple
Operating System: | Difficulty: Unknown
Unknown/Multiple | Blocked By:
Type of failure: GHC | Related Tickets:
rejects valid program |
Test Case: |
Blocking: |
Differential Revisions: |
-------------------------------------+-------------------------------------
Changes (by thomie):
* component: Compiler => Compiler (Type checker)
Comment:
The error message for the code from the description is improved using ghc
HEAD. A regression test should be added.
{{{
$ ghc-7.9.20141115 test.hs
[1 of 1] Compiling TTE ( test.hs, test.o )
test.hs:6:10:
Bad call to tagToEnum# at type r_alE
Specify the type by giving a type signature
e.g. (tagToEnum# x) :: Bool
In the expression: tagToEnum# 1#
In the expression:
case tagToEnum# 1# of {
True -> "True"
False -> "False" }
In an equation for ‘f’:
f = case tagToEnum# 1# of {
True -> "True"
False -> "False" }
}}}
See also commit 706c439fb5d3f1e30ad7b3953fde17dd01dae1bc:
{{{
Author: simonpj
participants (1)
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