Merge branch 'reorganize'

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diff --git a/dhall/src/error/text/HandlerInputTypeMismatch.txt b/dhall/src/error/text/HandlerInputTypeMismatch.txt
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+Explanation: You can ❰merge❱ the alternatives of a union using a record with one
+handler per alternative, like this:
+
+
+    ┌─────────────────────────────────────────────────────────────────────┐
+    │     let union    = < Left = +2 | Right : Bool >                     │
+    │ in  let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
+    │ in  merge handlers union : Bool                                     │
+    └─────────────────────────────────────────────────────────────────────┘
+
+
+... as long as the input type of each handler function matches the type of the
+corresponding alternative:
+
+
+    ┌───────────────────────────────────────────────────────────┐
+    │ union    : < Left : Natural       | Right : Bool        > │
+    └───────────────────────────────────────────────────────────┘
+                          ⇧                       ⇧
+                   These must match        These must match
+                          ⇩                       ⇩
+    ┌───────────────────────────────────────────────────────────┐
+    │ handlers : { Left : Natural → Bool, Right : Bool → Bool } │
+    └───────────────────────────────────────────────────────────┘
+
+
+For example, the following expression is $_NOT valid:
+
+
+      Invalid: Doesn't match the type of the ❰Right❱ alternative
+                                                               ⇩
+    ┌──────────────────────────────────────────────────────────────────────┐
+    │     let handlers = { Left = Natural/even | Right = λ(x : Text) → x } │
+    │ in  let union    = < Left = +2 | Right : Bool >                      │
+    │ in  merge handlers union : Bool                                      │
+    └──────────────────────────────────────────────────────────────────────┘
+
+
+Your handler for the following alternative:
+
+↳ $txt0
+
+... needs to accept an input value of type:
+
+↳ $txt1
+
+... but actually accepts an input value of a different type:
+
+↳ $txt2