... | @@ -238,7 +238,8 @@ Pros: |
... | @@ -238,7 +238,8 @@ Pros: |
|
|
|
|
|
Cons:
|
|
Cons:
|
|
|
|
|
|
- Potential trouble with inference of type family arguments. The type family has to be injective, which can be guaranteed in practice
|
|
- Potential trouble with inference of type family arguments. The `WrapL` type family has to be injective, which can be guaranteed in practice
|
|
|
|
-
|
|
|
|
|
|
## An example to illustrate
|
|
## An example to illustrate
|
|
|
|
|
... | @@ -284,6 +285,8 @@ module BasicGHCTypes where |
... | @@ -284,6 +285,8 @@ module BasicGHCTypes where |
|
data Phase = Ps | Rn | Tc
|
|
data Phase = Ps | Rn | Tc
|
|
data GHC (p :: Phase)
|
|
data GHC (p :: Phase)
|
|
|
|
|
|
|
|
data TH
|
|
|
|
|
|
data NoExt = NoExt
|
|
data NoExt = NoExt
|
|
data NoNewCon
|
|
data NoNewCon
|
|
|
|
|
... | @@ -301,7 +304,7 @@ data SrcSpan -- = the definition of SrcSpan |
... | @@ -301,7 +304,7 @@ data SrcSpan -- = the definition of SrcSpan |
|
data Located a = L SrcSpan a
|
|
data Located a = L SrcSpan a
|
|
|
|
|
|
noSrcSpan :: SrcSpan
|
|
noSrcSpan :: SrcSpan
|
|
noSrcSpan = ... -- an empty SrcSpan
|
|
noSrcSpan = undefined -- an empty SrcSpan
|
|
|
|
|
|
type family XAppGHC (p :: Phase)
|
|
type family XAppGHC (p :: Phase)
|
|
type instance XAppGHC Ps = NoExt
|
|
type instance XAppGHC Ps = NoExt
|
... | @@ -333,7 +336,7 @@ family. |
... | @@ -333,7 +336,7 @@ family. |
|
|
|
|
|
|
|
|
|
Here is a representation of lambda expressions in the ping-pong style.
|
|
Here is a representation of lambda expressions in the ping-pong style.
|
|
Unfortunately, this forces us to redefine the base TTG data type,
|
|
Unfortunately, this forces us to redefine the base TTG data type for e.g. TH,
|
|
forcing it into ping-pong style, which is why we don't like it for the reasons mentioned above.
|
|
forcing it into ping-pong style, which is why we don't like it for the reasons mentioned above.
|
|
|
|
|
|
|
|
|
... | @@ -375,69 +378,17 @@ type instance XNew (GHC p) = XNewGHC p |
... | @@ -375,69 +378,17 @@ type instance XNew (GHC p) = XNewGHC p |
|
type instance XId (GHC p) = XIdGHC p
|
|
type instance XId (GHC p) = XIdGHC p
|
|
|
|
|
|
-- ----------------------------------------------
|
|
-- ----------------------------------------------
|
|
-- Example Function
|
|
-- TH-Specific Decorations
|
|
-- ----------------------------------------------
|
|
|
|
par :: LExp (GHC x) -> LExp (GHC x)
|
|
|
|
par l@(L sp (App{})) = L sp (Par NoExt l)
|
|
|
|
par l = l
|
|
|
|
```
|
|
|
|
|
|
|
|
### Ping-pong style revamped (solution D)
|
|
|
|
|
|
|
|
Here's an example for solution D:
|
|
|
|
|
|
|
|
### Ping-pong style
|
|
|
|
|
|
|
|
|
|
|
|
Here is a representation of lambda expressions in the ping-pong style.
|
|
|
|
Unfortunately, this forces us to redefine the base TTG data type,
|
|
|
|
forcing it into ping-pong style, which is why we don't like it for the reasons mentioned above.
|
|
|
|
|
|
|
|
|
|
|
|
```
|
|
|
|
{-# OPTIONS_GHC -Wall -fno-warn-unticked-promoted-constructors #-}
|
|
|
|
{-# LANGUAGE TypeFamilies, DataKinds #-}
|
|
|
|
|
|
|
|
module Original where
|
|
|
|
|
|
|
|
import BasicGHCTypes
|
|
|
|
|
|
|
|
-- | Only wraps a `Located` around `f` when `p` is a `GhcPass`.
|
|
|
|
type family WrapL p (f :: * -> *) = r | r -> p f where
|
|
|
|
WrapL (GhcPass p) f = Located (f (GhcPass p))
|
|
|
|
-- This bogus instance is unfortunate, but needed for injectivity and thus
|
|
|
|
-- type inference.
|
|
|
|
WrapL p Located = Located (Located p)
|
|
|
|
WrapL p f = f p
|
|
|
|
|
|
|
|
-- ----------------------------------------------
|
|
|
|
-- AST Base
|
|
|
|
-- ----------------------------------------------
|
|
-- ----------------------------------------------
|
|
type LExp x = WrapL x Exp
|
|
type instance WrapL TH f = f TH
|
|
|
|
|
|
data Exp x -- Notice the alternation between LExp and Exp
|
|
|
|
= Var (XVar x) (XId x)
|
|
|
|
| Abs (XAbs x) (XId x) (LExp x)
|
|
|
|
| App (XApp x) (LExp x) (LExp x)
|
|
|
|
| Par (XPar x) (LExp x)
|
|
|
|
| New (XNew x) -- The extension constructor
|
|
|
|
|
|
|
|
type family XVar x
|
|
|
|
type family XAbs x
|
|
|
|
type family XApp x
|
|
|
|
type family XPar x
|
|
|
|
type family XNew x
|
|
|
|
type family XId x
|
|
|
|
|
|
|
|
-- ----------------------------------------------
|
|
-- Or whatever the instances for TH are
|
|
-- GHC-Specific Decorations
|
|
type instance XVar TH = NoExt
|
|
-- ----------------------------------------------
|
|
type instance XAbs TH = NoExt
|
|
type instance XVar (GHC _) = NoExt
|
|
type instance XApp TH = NoExt
|
|
type instance XAbs (GHC _) = NoExt
|
|
type instance XPar TH = NoExt
|
|
type instance XApp (GHC p) = XAppGHC p
|
|
type instance XNew TH = NoExt
|
|
type instance XPar (GHC _) = NoExt
|
|
type instance XId TH = NoExt
|
|
type instance XNew (GHC p) = XNewGHC p
|
|
|
|
type instance XId (GHC p) = XIdGHC p
|
|
|
|
|
|
|
|
-- ----------------------------------------------
|
|
-- ----------------------------------------------
|
|
-- Example Function
|
|
-- Example Function
|
... | @@ -445,6 +396,13 @@ type instance XId (GHC p) = XIdGHC p |
... | @@ -445,6 +396,13 @@ type instance XId (GHC p) = XIdGHC p |
|
par :: LExp (GHC x) -> LExp (GHC x)
|
|
par :: LExp (GHC x) -> LExp (GHC x)
|
|
par l@(L sp (App{})) = L sp (Par NoExt l)
|
|
par l@(L sp (App{})) = L sp (Par NoExt l)
|
|
par l = l
|
|
par l = l
|
|
|
|
|
|
|
|
-- ----------------------------------------------
|
|
|
|
-- Example Function in TH
|
|
|
|
-- ----------------------------------------------
|
|
|
|
parTH :: LExp TH -> LExp TH
|
|
|
|
parTH l@(L sp (App{})) = L sp (Par NoExt l) -- Yikes! TH doesn't care for SrcLocs...
|
|
|
|
parTH l = l
|
|
```
|
|
```
|
|
|
|
|
|
### The SrcSpan Accessor Typeclass
|
|
### The SrcSpan Accessor Typeclass
|
... | @@ -622,6 +580,85 @@ par l@(LL sp (App{})) = Par (L sp NoExt) l |
... | @@ -622,6 +580,85 @@ par l@(LL sp (App{})) = Par (L sp NoExt) l |
|
par l = l
|
|
par l = l
|
|
```
|
|
```
|
|
|
|
|
|
|
|
### Solution D - Example Code
|
|
|
|
|
|
|
|
|
|
|
|
In the code below, as compared to the old ping-pong style, we have the following key changes:
|
|
|
|
|
|
|
|
- `LExp` becomes `WrapL x Exp` and reduces to `Located (Exp x)` for `x ~ GHC p` and to `Exp x` for `x ~ TH`
|
|
|
|
- That's it
|
|
|
|
|
|
|
|
```
|
|
|
|
{-# OPTIONS_GHC -Wall -fno-warn-unticked-promoted-constructors #-}
|
|
|
|
{-# LANGUAGE TypeFamilies, TypeFamilyDependencies, DataKinds #-}
|
|
|
|
|
|
|
|
module SolutionD where
|
|
|
|
|
|
|
|
import BasicGHCTypes
|
|
|
|
|
|
|
|
-- | We use this to only wrap a `Located` around `f` when `p` is `GHC`.
|
|
|
|
-- Injectivity is important for inference.
|
|
|
|
type family WrapL p (f :: * -> *) = r | r -> p f
|
|
|
|
|
|
|
|
-- ----------------------------------------------
|
|
|
|
-- AST Base
|
|
|
|
-- ----------------------------------------------
|
|
|
|
type LExp x = WrapL x Exp
|
|
|
|
|
|
|
|
data Exp x -- Notice the alternation between LExp and Exp
|
|
|
|
= Var (XVar x) (XId x)
|
|
|
|
| Abs (XAbs x) (XId x) (LExp x)
|
|
|
|
| App (XApp x) (LExp x) (LExp x)
|
|
|
|
| Par (XPar x) (LExp x)
|
|
|
|
| New (XNew x) -- The extension constructor
|
|
|
|
|
|
|
|
type family XVar x
|
|
|
|
type family XAbs x
|
|
|
|
type family XApp x
|
|
|
|
type family XPar x
|
|
|
|
type family XNew x
|
|
|
|
type family XId x
|
|
|
|
|
|
|
|
-- ----------------------------------------------
|
|
|
|
-- GHC-Specific Decorations
|
|
|
|
-- ----------------------------------------------
|
|
|
|
type instance WrapL (GHC p) f = Located (f (GHC p))
|
|
|
|
|
|
|
|
type instance XVar (GHC _) = NoExt
|
|
|
|
type instance XAbs (GHC _) = NoExt
|
|
|
|
type instance XApp (GHC p) = XAppGHC p
|
|
|
|
type instance XPar (GHC _) = NoExt
|
|
|
|
type instance XNew (GHC p) = XNewGHC p
|
|
|
|
type instance XId (GHC p) = XIdGHC p
|
|
|
|
|
|
|
|
-- ----------------------------------------------
|
|
|
|
-- TH-Specific Decorations
|
|
|
|
-- ----------------------------------------------
|
|
|
|
type instance WrapL TH f = f TH
|
|
|
|
|
|
|
|
-- Or whatever the instances for TH are
|
|
|
|
type instance XVar TH = NoExt
|
|
|
|
type instance XAbs TH = NoExt
|
|
|
|
type instance XApp TH = NoExt
|
|
|
|
type instance XPar TH = NoExt
|
|
|
|
type instance XNew TH = NoExt
|
|
|
|
type instance XId TH = NoExt
|
|
|
|
|
|
|
|
-- ----------------------------------------------
|
|
|
|
-- Example Function
|
|
|
|
-- ----------------------------------------------
|
|
|
|
par :: LExp (GHC x) -> LExp (GHC x)
|
|
|
|
par l@(L sp (App{})) = L sp (Par NoExt l)
|
|
|
|
par l = l
|
|
|
|
|
|
|
|
-- ----------------------------------------------
|
|
|
|
-- Example Function in TH
|
|
|
|
-- ----------------------------------------------
|
|
|
|
parTH :: LExp TH -> LExp TH
|
|
|
|
parTH l@App{} = Par NoExt l -- Nice!
|
|
|
|
parTH l = l
|
|
|
|
```
|
|
|
|
|
|
## Implementation Details
|
|
## Implementation Details
|
|
|
|
|
|
### General Plan
|
|
### General Plan
|
... | | ... | |