Lifting a function from where clause to top level causes compilation time to triple
I have this program that depends on the library "red-black-record" version 2.0.2.2 on Hackage:
{-# LANGUAGE DataKinds, TypeApplications #-}
module Main where
import Data.RBR (FromList,Delete,Variant,I,injectI,winnowI,match)
import GHC.TypeLits
type Phase01 = FromList '[
'("ctor1",Int), '("ctor2",Bool), '("ctor4",Char), '("ctor3",Char),
'("ctor6",Char), '("ctor5",Char), '("ctor10",Char), '("ctor11",Char),
'("ctor13",Char), '("ctor14",Char), '("ctor39",Char), '("ctor46",Char),
'("ctor47",Char), '("ctor44",Char), '("ctor43",Char), '("ctor7",Char),
'("ctor9",Char), '("ctor20",Char), '("ctor45",Char), '("ctor21",Char),
'("ctor48",Char), '("ctor49",Char), '("ctor50",Char), '("ctor41",Char),
'("ctor33",Char), '("ctor32",Char), '("ctor42",Char), '("ctor22",Char),
'("ctor23",Char), '("ctor8",Char), '("ctor40",Char), '("ctor29",Char),
'("ctor24",Char), '("ctor38",Char), '("ctor25",Char), '("ctor26",Char),
'("ctor27",Char), '("ctor28",Char), '("ctor36",Char), '("ctor52",Char),
'("ctor51",Char), '("ctor53",Char), '("ctor12",Char), '("ctor54",Char),
'("ctor15",Char), '("ctor31",Char), '("ctor30",Char), '("ctor34",Char),
'("ctor35",Char), '("ctor17",Char), '("ctor16",Char), '("ctor18",Char),
'("ctor19",Char), '("ctor37",Char)
]
type Phase02 = Delete "ctor1" Int Phase01
main :: IO ()
main = print (match @"ctor17" (fromPhase1ToPhase2 (injectI @"ctor1" 2)))
where
fromPhase1ToPhase2 :: Variant I Phase01 -> Variant I Phase02
fromPhase1ToPhase2 v = case winnowI @"ctor1" @Int v of
Right z -> injectI @"ctor2" False
Left l -> l
"red-black-record" provides extensible variants; the code is basically removing a branch from a variant with 50-plus branches, and then trying to match another branch. It is type family-heavy code.
The code as it is takes **~9 seconds** to compile on my machine. But when I move the fromPhase1ToPhase2
function to the top level (including the signature) compilation time balloons to **~ 29 seconds**. Is there a reason it should be so?
As another datapoint, moving the function to the top level but omitting the complex type-level map parameters (Phase01
, Phase02
) using partial type signatures (also requires a new type application) compiles in **~9 seconds** again.
{-# LANGUAGE PartialTypeSignatures #-}
{-# OPTIONS_GHC -Wno-partial-type-signatures #-}
-- ...
type Phase02 = Delete "ctor1" Int Phase01
fromPhase1ToPhase2 :: Variant I _ -> Variant I _
fromPhase1ToPhase2 v = case winnowI @"ctor1" @Int @Phase01 v of
Right z -> injectI @"ctor2" False
Left l -> l
main :: IO ()
main = print (match @"ctor17" (fromPhase1ToPhase2 (injectI @"ctor1" 2)))
Trac metadata
Trac field | Value |
---|---|
Version | 8.4.2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |