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<div name="messageBodySection" style="font-size: 14px; font-family: -apple-system, BlinkMacSystemFont, sans-serif;">Hi,
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<div>The function `join` flattens a double-layered monad into one layer and its type signature is </div>
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<div> join :: (Monad m) => m (m a) -> m a</div>
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<div>But when the first argument supplied is `(,)`, the type signature becomes </div>
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<div> join (,) :: b -> (b, b)</div>
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<div>in ghci. The monad constraint is lost when supplied the first argument. So my question is why the type constraint is lost and what monad is supplied here.</div>
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Regards,
<div>Qingbo Liu</div>
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