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# Pattern Synonyms
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Pattern synonyms were (most recently, at least) proposed by Conor McBride at the Haskell' list. Briefly:
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> Hi folks
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> Having spent the last week hacking, I've found a common irritation, so I have a proposal to mitigate it. Of course, this issue may not bug anyone else, so I'm a little
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> hesitant. In pessimal pedagogical order, the proposal: pattern synonyms. I want to be allowed to write stuff like
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> ```wiki
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> P x y z = C x (y, [z])
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> ```
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> defining a capitalised symbol with parameters used linearly in a pattern on the right-hand side. Pattern synonyms should be fully applied and expand macro-style wherever
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> patterns or terms appear, hence should not give rise to cycles, just like type synonyms.
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> It seems (and is) trivial. Why would it help? Well, it would help me, because I often write more complex types than strictly necessary to represent data in order to expose
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> its structure and thus gain free equipment.
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Note that the original suggestion was that pattern synonyms also would be allowed as expressions, for construction.
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(In that context, one might want an underscore to stand for undefined.)
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This is related to [Views](views).
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