codesnippets:fnowarnorphans
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| codesnippets:fnowarnorphans [2021/04/10 20:45] – created f2b216 | codesnippets:fnowarnorphans [2025/10/08 00:48] (current) – external edit 127.0.0.1 | ||
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| ====== {-# OPTIONS_GHC -fno-warn-orphans #-} ====== | ====== {-# OPTIONS_GHC -fno-warn-orphans #-} ====== | ||
| + | ~~DISCUSSION~~ | ||
| * prevents warnings of orphan instance, meaning: | * prevents warnings of orphan instance, meaning: | ||
| * instance declaration of a type is not declared in the module of the class | * instance declaration of a type is not declared in the module of the class | ||
| + | * NOTE: Orphan instances may be useful. | ||
| + | * see also [[https:// | ||
| + | * NOTE: The purpose of the examples here is only to demonstrate the impact on the compiler. The examples may not make sense as a use case of type classes. | ||
| + | * example that may make more sense: [[codesnippets: | ||
| * example: | * example: | ||
| * code of module Lib:< | * code of module Lib:< | ||
| Line 35: | Line 40: | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^... | | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^... | ||
| </ | </ | ||
| + | * example, with GHC option: | ||
| + | * code:< | ||
| + | {-# OPTIONS_GHC -fno-warn-orphans #-} | ||
| + | import Lib (MyClass(..)) | ||
| + | |||
| + | main :: IO () | ||
| + | main = print x1 | ||
| + | |||
| + | instance MyClass Double where | ||
| + | fMy x = (x * x) + x + 1 | ||
| + | |||
| + | x1 :: Double | ||
| + | x1 = fMy 3.4 | ||
| + | </ | ||
| + | * compiles, error and warning free, with compiler: GHC 8.10.4, using compiler option -Wall | ||
| + | * executes, with output:< | ||
| + | 15.959999999999999 | ||
| + | </ | ||
| + | |||
| + | |||
| + | ===== ✎ ===== | ||
| + | ~~DISCUSSION~~ | ||
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