Add docs for GHC-04584

Author: TauOmicronMu

message-index/messages/GHC-04584/index.md

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+---
+title: Expression syntax in pattern
+summary: There has been an attempt to pattern match on Expression syntax. 
+severity: error
+introduced: 9.6.1
+---
+
+## Example Text
+
+```   
+Expression syntax in pattern: [1 .. 10]
+```
+

message-index/messages/GHC-04584/matchingdots/after/Matchingdots.hs

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+module Matchingdots where
+
+-- If the input is [1..10], return 0, otherwise return 1 
+f :: [Int] -> Int
+f xs 
+    | xs == [1..10] = 0 
+    | otherwise = 1      
+

message-index/messages/GHC-04584/matchingdots/before/Matchingdots.hs

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+module Matchingdots where
+
+-- If the input is [1..10], return 0, otherwise return 1 
+f :: [Int] -> Int
+f [1..10] = 0 
+f _ = 1 
+

message-index/messages/GHC-04584/matchingdots/index.md

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+---
+title: Using .. in pattern 
+---
+
+When pattern matching, Expressions are not allowed as patterns to be matched against. Instead, consider matching on a list, and using a conditional. 
+
+
+# Error Message
+
+```
+before_dots.hs:3:3: error: [GHC-04584]
+    Expression syntax in pattern: [1 .. 10]
+  |
+3 | f [1..10] = 0 
+  |   ^^^^^^^
+```