Visible type application

This re-working of the typechecker algorithm is based on
the paper "Visible type application", by Richard Eisenberg,
Stephanie Weirich, and Hamidhasan Ahmed, to be published at
ESOP'16.

This patch introduces -XTypeApplications, which allows users
to say, for example `id @Int`, which has type `Int -> Int`. See
the changes to the user manual for details.

This patch addresses tickets #10619, #5296, #10589.

1 files changed, 67 insertions, 41 deletions

diff --git a/testsuite/tests/ado/ado002.stderr b/testsuite/tests/ado/ado002.stderr
index cdfdbc4b19..9e7eba0a67 100644
--- a/testsuite/tests/ado/ado002.stderr
+++ b/testsuite/tests/ado/ado002.stderr
@@ -1,55 +1,81 @@
 
 ado002.hs:8:8: error:
-    Couldn't match expected type ‘Char -> IO t1’
-                with actual type ‘IO Char’
-    The function ‘getChar’ is applied to one argument,
-    but its type ‘IO Char’ has none
-    In a stmt of a 'do' block: y <- getChar 'a'
-    In the expression:
-      do { x <- getChar;
-           y <- getChar 'a';
-           print (x, y) }
+    • Couldn't match expected type ‘Char -> IO t1’
+                  with actual type ‘IO Char’
+    • The function ‘getChar’ is applied to one argument,
+      but its type ‘IO Char’ has none
+      In a stmt of a 'do' block: y <- getChar 'a'
+      In the expression:
+        do { x <- getChar;
+             y <- getChar 'a';
+             print (x, y) }
 
 ado002.hs:9:3: error:
-    Couldn't match type ‘()’ with ‘Int’
-    Expected type: IO Int
-      Actual type: IO ()
-    In a stmt of a 'do' block: print (x, y)
-    In the expression:
-      do { x <- getChar;
-           y <- getChar 'a';
-           print (x, y) }
+    • Couldn't match type ‘()’ with ‘Int’
+      Expected type: IO Int
+        Actual type: IO ()
+    • In a stmt of a 'do' block: print (x, y)
+      In the expression:
+        do { x <- getChar;
+             y <- getChar 'a';
+             print (x, y) }
+      In an equation for ‘f’:
+          f = do { x <- getChar;
+                   y <- getChar 'a';
+                   print (x, y) }
 
 ado002.hs:15:11: error:
-    Couldn't match expected type ‘Int’ with actual type ‘Char’
-    In the expression: y
-    In a stmt of a 'do' block: return (y, x)
+    • Couldn't match expected type ‘Int’ with actual type ‘Char’
+    • In the expression: y
+      In a stmt of a 'do' block: return (y, x)
+      In the expression:
+        do { x <- getChar;
+             y <- getChar;
+             return (y, x) }
 
 ado002.hs:15:13: error:
-    Couldn't match expected type ‘Int’ with actual type ‘Char’
-    In the expression: x
-    In a stmt of a 'do' block: return (y, x)
+    • Couldn't match expected type ‘Int’ with actual type ‘Char’
+    • In the expression: x
+      In a stmt of a 'do' block: return (y, x)
+      In the expression:
+        do { x <- getChar;
+             y <- getChar;
+             return (y, x) }
 
 ado002.hs:23:9: error:
-    Couldn't match expected type ‘Char -> IO t0’
-                with actual type ‘IO Char’
-    The function ‘getChar’ is applied to one argument,
-    but its type ‘IO Char’ has none
-    In a stmt of a 'do' block: x5 <- getChar x4
-    In the expression:
-      do { x1 <- getChar;
-           x2 <- getChar;
-           x3 <- const (return ()) x1;
-           x4 <- getChar;
-           x5 <- getChar x4;
-           return (x2, x4) }
+    • Couldn't match expected type ‘Char -> IO t0’
+                  with actual type ‘IO Char’
+    • The function ‘getChar’ is applied to one argument,
+      but its type ‘IO Char’ has none
+      In a stmt of a 'do' block: x5 <- getChar x4
+      In the expression:
+        do { x1 <- getChar;
+             x2 <- getChar;
+             x3 <- const (return ()) x1;
+             x4 <- getChar;
+             x5 <- getChar x4;
+             return (x2, x4) }
 
 ado002.hs:24:11: error:
-    Couldn't match expected type ‘Int’ with actual type ‘Char’
-    In the expression: x2
-    In a stmt of a 'do' block: return (x2, x4)
+    • Couldn't match expected type ‘Int’ with actual type ‘Char’
+    • In the expression: x2
+      In a stmt of a 'do' block: return (x2, x4)
+      In the expression:
+        do { x1 <- getChar;
+             x2 <- getChar;
+             x3 <- const (return ()) x1;
+             x4 <- getChar;
+             x5 <- getChar x4;
+             return (x2, x4) }
 
 ado002.hs:24:14: error:
-    Couldn't match expected type ‘Int’ with actual type ‘Char’
-    In the expression: x4
-    In a stmt of a 'do' block: return (x2, x4)
+    • Couldn't match expected type ‘Int’ with actual type ‘Char’
+    • In the expression: x4
+      In a stmt of a 'do' block: return (x2, x4)
+      In the expression:
+        do { x1 <- getChar;
+             x2 <- getChar;
+             x3 <- const (return ()) x1;
+             x4 <- getChar;
+             x5 <- getChar x4;
+             return (x2, x4) }