Implement qualified do

This allows do blocks to be qualified with the namespace that the (>>=)
operator is defined in. Inspired by Purescript's version of the same
thing, and this ghc proposal:
https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0216-qualified-do.rst

CHANGELOG.md

@@ -20,6 +20,8 @@ Language changes:
 * Add `import X as Y`
    + This imports the module `X`, adding aliases for the definitions in
      namespace `Y`, so they can be referred to as `Y`.
+* `do` notation can now be qualified with a namespace
+   + `MyDo.do` opens a `do` block where the `>>=` operator used is `MyDo.(>>=)`
 
 Library changes:
 

src/Idris/Desugar.idr

@@ -269,8 +269,8 @@ mutual
       = pure $ IMustUnify fc UserDotted !(desugarB side ps x)
   desugarB side ps (PImplicit fc) = pure $ Implicit fc True
   desugarB side ps (PInfer fc) = pure $ Implicit fc False
-  desugarB side ps (PDoBlock fc block)
+  desugarB side ps (PDoBlock fc ns block)
-      = expandDo side ps fc block
+      = expandDo side ps fc ns block
   desugarB side ps (PBang fc term)
       = do itm <- desugarB side ps term
            bs <- get Bang
@@ -319,7 +319,7 @@ mutual
                    [PatClause fc (IVar fc (UN "True")) !(desugar side ps t),
                     PatClause fc (IVar fc (UN "False")) !(desugar side ps e)]
   desugarB side ps (PComprehension fc ret conds)
-      = desugarB side ps (PDoBlock fc (map guard conds ++ [toPure ret]))
+      = desugarB side ps (PDoBlock fc Nothing (map guard conds ++ [toPure ret]))
     where
       guard : PDo -> PDo
       guard (DoExp fc tm) = DoExp fc (PApp fc (PRef fc (UN "guard")) tm)
@@ -379,56 +379,61 @@ mutual
       = pure $ apply (IVar fc (UN "::"))
                 [!(desugarB side ps x), !(expandList side ps fc xs)]
 
+  addNS : Maybe (List String) -> Name -> Name
+  addNS (Just ns) n@(NS _ _) = n
+  addNS (Just ns) n = NS ns n
+  addNS _ n = n
+
   expandDo : {auto s : Ref Syn SyntaxInfo} ->
              {auto c : Ref Ctxt Defs} ->
              {auto u : Ref UST UState} ->
              {auto m : Ref MD Metadata} ->
-             Side -> List Name -> FC -> List PDo -> Core RawImp
+             Side -> List Name -> FC -> Maybe (List String) -> List PDo -> Core RawImp
-  expandDo side ps fc [] = throw (GenericMsg fc "Do block cannot be empty")
+  expandDo side ps fc ns [] = throw (GenericMsg fc "Do block cannot be empty")
-  expandDo side ps _ [DoExp fc tm] = desugar side ps tm
+  expandDo side ps _ _ [DoExp fc tm] = desugar side ps tm
-  expandDo side ps fc [e]
+  expandDo side ps fc ns [e]
       = throw (GenericMsg (getLoc e)
                   "Last statement in do block must be an expression")
-  expandDo side ps topfc (DoExp fc tm :: rest)
+  expandDo side ps topfc ns (DoExp fc tm :: rest)
       = do tm' <- desugar side ps tm
-           rest' <- expandDo side ps topfc rest
+           rest' <- expandDo side ps topfc ns rest
            -- A free standing 'case' block must return ()
            let ty = case tm' of
                          ICase _ _ _ _ => IVar fc (UN "Unit")
                          _ => Implicit fc False
            gam <- get Ctxt
-           pure $ IApp fc (IApp fc (IVar fc (UN ">>=")) tm')
+           pure $ IApp fc (IApp fc (IVar fc (addNS ns (UN ">>="))) tm')
                           (ILam fc top Explicit Nothing
                                 ty rest')
-  expandDo side ps topfc (DoBind fc n tm :: rest)
+  expandDo side ps topfc ns (DoBind fc n tm :: rest)
       = do tm' <- desugar side ps tm
-           rest' <- expandDo side ps topfc rest
+           rest' <- expandDo side ps topfc ns rest
-           pure $ IApp fc (IApp fc (IVar fc (UN ">>=")) tm')
+           pure $ IApp fc (IApp fc (IVar fc (addNS ns (UN ">>="))) tm')
                      (ILam fc top Explicit (Just n)
                            (Implicit fc False) rest')
-  expandDo side ps topfc (DoBindPat fc pat exp alts :: rest)
+  expandDo side ps topfc ns (DoBindPat fc pat exp alts :: rest)
       = do pat' <- desugar LHS ps pat
            (newps, bpat) <- bindNames False pat'
            exp' <- desugar side ps exp
            alts' <- traverse (desugarClause ps True) alts
            let ps' = newps ++ ps
-           rest' <- expandDo side ps' topfc rest
+           rest' <- expandDo side ps' topfc ns rest
-           pure $ IApp fc (IApp fc (IVar fc (UN ">>=")) exp')
+           pure $ IApp fc (IApp fc (IVar fc (addNS ns (UN ">>="))) exp')
                     (ILam fc top Explicit (Just (MN "_" 0))
                           (Implicit fc False)
                           (ICase fc (IVar fc (MN "_" 0))
                                (Implicit fc False)
                                (PatClause fc bpat rest'
                                   :: alts')))
-  expandDo side ps topfc (DoLet fc n rig ty tm :: rest)
+  expandDo side ps topfc ns (DoLet fc n rig ty tm :: rest)
       = do b <- newRef Bang initBangs
            tm' <- desugarB side ps tm
            ty' <- desugar side ps ty
-           rest' <- expandDo side ps topfc rest
+           rest' <- expandDo side ps topfc ns rest
            let bind = ILet fc rig n ty' tm' rest'
            bd <- get Bang
            pure $ bindBangs (bangNames bd) bind
-  expandDo side ps topfc (DoLetPat fc pat ty tm alts :: rest)
+  expandDo side ps topfc ns (DoLetPat fc pat ty tm alts :: rest)
       = do b <- newRef Bang initBangs
            pat' <- desugar LHS ps pat
            ty' <- desugar side ps ty
@@ -436,18 +441,18 @@ mutual
            tm' <- desugarB side ps tm
            alts' <- traverse (desugarClause ps True) alts
            let ps' = newps ++ ps
-           rest' <- expandDo side ps' topfc rest
+           rest' <- expandDo side ps' topfc ns rest
            bd <- get Bang
            pure $ bindBangs (bangNames bd) $
                     ICase fc tm' ty'
                        (PatClause fc bpat rest'
                                   :: alts')
-  expandDo side ps topfc (DoLetLocal fc decls :: rest)
+  expandDo side ps topfc ns (DoLetLocal fc decls :: rest)
-      = do rest' <- expandDo side ps topfc rest
+      = do rest' <- expandDo side ps topfc ns rest
            decls' <- traverse (desugarDecl ps) decls
            pure $ ILocal fc (concat decls') rest'
-  expandDo side ps topfc (DoRewrite fc rule :: rest)
+  expandDo side ps topfc ns (DoRewrite fc rule :: rest)
-      = do rest' <- expandDo side ps topfc rest
+      = do rest' <- expandDo side ps topfc ns rest
            rule' <- desugar side ps rule
            pure $ IRewrite fc rule' rest'
 

src/Idris/Parser.idr

@@ -122,11 +122,11 @@ mutual
   appExpr : ParseOpts -> FileName -> IndentInfo -> Rule PTerm
   appExpr q fname indents
       = case_ fname indents
+    <|> doBlock fname indents
     <|> lambdaCase fname indents
     <|> lazy fname indents
     <|> if_ fname indents
     <|> with_ fname indents
-    <|> doBlock fname indents
     <|> do start <- location
            f <- simpleExpr fname indents
            args <- many (argExpr q fname indents)
@@ -740,7 +740,17 @@ mutual
            actions <- block (doAct fname)
            end <- location
            end <- pure $ fromMaybe end $ map (endPos . getLoc) $ join $ last' <$> last' actions
-           pure (PDoBlock (MkFC fname start end) (concat actions))
+           pure (PDoBlock (MkFC fname start end) Nothing (concat actions))
+    <|> do start <- location
+           nsdo <- namespacedIdent
+           the (SourceEmptyRule PTerm) $ case nsdo of
+                ("do" :: ns) =>
+                   do actions <- block (doAct fname)
+                      end <- location
+                      end <- pure $ fromMaybe end $ map (endPos . getLoc) $ join $ last' <$> last' actions
+                      pure (PDoBlock (MkFC fname start end)
+                                     (Just (reverse ns)) (concat actions))
+                _ => fail "Not a namespaced 'do'"
 
   lowerFirst : String -> Bool
   lowerFirst "" = False

src/Idris/Syntax.idr

@@ -76,7 +76,7 @@ mutual
 
        -- Syntactic sugar
 
-       PDoBlock : FC -> List PDo -> PTerm
+       PDoBlock : FC -> Maybe (List String) -> List PDo -> PTerm
        PBang : FC -> PTerm -> PTerm
        PIdiom : FC -> PTerm -> PTerm
        PList : FC -> List PTerm -> PTerm
@@ -135,7 +135,7 @@ mutual
   getPTermLoc (PSectionR fc _ _) = fc
   getPTermLoc (PEq fc _ _) = fc
   getPTermLoc (PBracketed fc _) = fc
-  getPTermLoc (PDoBlock fc _) = fc
+  getPTermLoc (PDoBlock fc _ _) = fc
   getPTermLoc (PBang fc _) = fc
   getPTermLoc (PIdiom fc _) = fc
   getPTermLoc (PList fc _) = fc
@@ -546,7 +546,7 @@ mutual
     showPrec d (PSectionR _ x op) = "(" ++ showPrec d x ++ " " ++ showPrec d op ++ ")"
     showPrec d (PEq fc l r) = showPrec d l ++ " = " ++ showPrec d r
     showPrec d (PBracketed _ tm) = "(" ++ showPrec d tm ++ ")"
-    showPrec d (PDoBlock _ ds)
+    showPrec d (PDoBlock _ ns ds)
         = "do " ++ showSep " ; " (map showDo ds)
     showPrec d (PBang _ tm) = "!" ++ showPrec d tm
     showPrec d (PIdiom _ tm) = "[|" ++ showPrec d tm ++ "|]"
@@ -828,8 +828,8 @@ mapPTermM f = goPTerm where
     goPTerm (PBracketed fc x) =
       PBracketed fc <$> goPTerm x
       >>= f
-    goPTerm (PDoBlock fc xs) =
+    goPTerm (PDoBlock fc ns xs) =
-      PDoBlock fc <$> goPDos xs
+      PDoBlock fc ns <$> goPDos xs
       >>= f
     goPTerm (PBang fc x) =
       PBang fc <$> goPTerm x

tests/Main.idr

@@ -40,6 +40,7 @@ idrisTests
        "basic026", "basic027", "basic028", "basic029", "basic030",
        "basic031", "basic032", "basic033", "basic034", "basic035",
        "basic036", "basic037", "basic038", "basic039", "basic040",
+       "basic041",
        -- Coverage checking
        "coverage001", "coverage002", "coverage003", "coverage004",
        "coverage005", "coverage006", "coverage007", "coverage008",

tests/idris2/basic041/QDo.idr

@@ -0,0 +1,9 @@
+namespace MyDo
+  export
+  (>>=) : a -> (a -> IO b) -> IO b
+  (>>=) val k = k val
+
+foo : IO ()
+foo = MyDo.do
+         x <- "Silly"
+         putStrLn x

tests/idris2/basic041/expected

@@ -0,0 +1 @@
+1/1: Building QDo (QDo.idr)

tests/idris2/basic041/run

@@ -0,0 +1,3 @@
+$1 --check QDo.idr
+
+rm -rf build