Cleanup error code

src/librustc_error_codes/error_codes/E0080.md

@@ -1,14 +1,18 @@
-This error indicates that the compiler was unable to sensibly evaluate a
-constant expression that had to be evaluated. Attempting to divide by 0
-or causing integer overflow are two ways to induce this error. For example:
+A constant value failed to get evaluated.
+
+Erroneous code example:
 
 ```compile_fail,E0080
 enum Enum {
     X = (1 << 500),
-    Y = (1 / 0)
+    Y = (1 / 0),
 }
 ```
 
+This error indicates that the compiler was unable to sensibly evaluate a
+constant expression that had to be evaluated. Attempting to divide by 0
+or causing an integer overflow are two ways to induce this error.
+
 Ensure that the expressions given can be evaluated as the desired integer type.
 See the FFI section of the Reference for more information about using a custom
 integer type:

src/librustc_error_codes/error_codes/E0081.md

@@ -1,21 +1,23 @@
-Enum discriminants are used to differentiate enum variants stored in memory.
-This error indicates that the same value was used for two or more variants,
-making them impossible to tell apart.
+A discrimant value is present more than once.
+
+Erroneous code example:
 
 ```compile_fail,E0081
-// Bad.
 enum Enum {
     P = 3,
-    X = 3,
+    X = 3, // error!
     Y = 5,
 }
 ```
 
+Enum discriminants are used to differentiate enum variants stored in memory.
+This error indicates that the same value was used for two or more variants,
+making it impossible to distinguish them.
+
 ```
-// Good.
 enum Enum {
     P,
-    X = 3,
+    X = 3, // ok!
     Y = 5,
 }
 ```
@@ -27,7 +29,7 @@ variants.
 ```compile_fail,E0081
 enum Bad {
     X,
-    Y = 0
+    Y = 0, // error!
 }
 ```
 

src/librustc_error_codes/error_codes/E0091.md

@@ -1,5 +1,6 @@
-You gave an unnecessary type or const parameter in a type alias. Erroneous
-code example:
+An unnecessary type or const parameter was given in a type alias.
+
+Erroneous code example:
 
 ```compile_fail,E0091
 type Foo<T> = u32; // error: type parameter `T` is unused