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, 13 insertions, 11 deletions

diff --git a/testsuite/tests/typecheck/should_fail/mc21.stderr b/testsuite/tests/typecheck/should_fail/mc21.stderr
index 3017d2221c..74a13b14bc 100644
--- a/testsuite/tests/typecheck/should_fail/mc21.stderr
+++ b/testsuite/tests/typecheck/should_fail/mc21.stderr
@@ -1,11 +1,13 @@
-

-mc21.hs:12:26: error:

-    Couldn't match type ‘a’ with ‘[a]’

-    ‘a’ is a rigid type variable bound by

-    a type expected by the context:

-      forall a. [a] -> [[a]]

-    at mc21.hs:11:9

-    Expected type: [a] -> [[a]]

-      Actual type: [[a]] -> [[a]]

-    In the expression: take 5

-    In a stmt of a monad comprehension: then group using take 5

+
+mc21.hs:12:26: error:
+    • Couldn't match type ‘a’ with ‘[a]’
+      ‘a’ is a rigid type variable bound by
+        a type expected by the context:
+          forall a. [a] -> [[a]]
+        at mc21.hs:11:9
+      Expected type: [a] -> [[a]]
+        Actual type: [[a]] -> [[a]]
+    • In the expression: take 5
+      In a stmt of a monad comprehension: then group using take 5
+      In the expression:
+        [GHC.List.length x | x <- [Gnorf, Brain], then group using take 5]