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Talk:TypeCompose - Revision history
2024-03-28T16:28:07Z
Revision history for this page on the wiki
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https://wiki.haskell.org/index.php?title=Talk:TypeCompose&diff=17187&oldid=prev
Wolfgang Jeltsch: addition of answer concerning App/Apply
2007-12-05T23:13:32Z
<p>addition of answer concerning App/Apply</p>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>No preference concerning <hask>App</hask> and <hask>Apply</hask> from my side at the moment.</div></td>
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Wolfgang Jeltsch
https://wiki.haskell.org/index.php?title=Talk:TypeCompose&diff=17185&oldid=prev
Conal: Reply to Wolfgang -- :$, :.
2007-12-05T17:15:56Z
<p>Reply to Wolfgang -- :$, :.</p>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Sorry, I <del class="diffchange diffchange-inline">hadn’t</del> looked that deeply into TypeCompose to discover App. Yes, this is what I meant.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Sorry, I <ins class="diffchange diffchange-inline">hadn't</ins> looked that deeply into TypeCompose to discover App. Yes, this is what I meant.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><hask>(:$)</hask> might be nice as its type constructor name (but not as its data constructor name since the data constructor is unary). But if we use <hask>(:$)</hask> instead of <hask>App</hask>, we should also use <hask>(:.)</hask> instead of <hask>O</hask>. In grapefruit-data, I had a module <hask>Data.Composition</hask> which used <hask>(:.:)</hask>. Actually, I <del class="diffchange diffchange-inline">don’t</del> like the <hask>O</hask>. While it looks similar to the function composition operator, it <del class="diffchange diffchange-inline">isn’t</del> the function composition operator. Instead, it is just a letter, and identifiers made of letters should be descriptive, in my opinion, like <hask>App</hask>, for example.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><hask>(:$)</hask> might be nice as its type constructor name (but not as its data constructor name since the data constructor is unary). But if we use <hask>(:$)</hask> instead of <hask>App</hask>, we should also use <hask>(:.)</hask> instead of <hask>O</hask>. In grapefruit-data, I had a module <hask>Data.Composition</hask> which used <hask>(:.:)</hask>. Actually, I <ins class="diffchange diffchange-inline">don't</ins> like the <hask>O</hask>. While it looks similar to the function composition operator, it <ins class="diffchange diffchange-inline">isn't</ins> the function composition operator. Instead, it is just a letter, and identifiers made of letters should be descriptive, in my opinion, like <hask>App</hask>, for example.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>I <del class="diffchange diffchange-inline">haven’t</del> played with <hask>(:*:)</hask> and its counterpart yet. No time. :-( </div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>I <ins class="diffchange diffchange-inline">haven't</ins> played with <hask>(:*:)</hask> and its counterpart yet. No time. :-( </div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>: Understood. I think you'll like it. [[User:Conal|Conal]] 17:15, 5 December 2007 (UTC)</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td>
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<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Grapefruit now dropped the modules <hask>Data.Monoid.Bonus</hask> and <hask>Data.Composition</hask> and uses TypeCompose&nbsp;0.2 instead.</div></td>
<td class="diff-marker"> </td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Grapefruit now dropped the modules <hask>Data.Monoid.Bonus</hask> and <hask>Data.Composition</hask> and uses TypeCompose&nbsp;0.2 instead.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>By the way, I <del class="diffchange diffchange-inline">don’t</del> like that in this wiki one <del class="diffchange diffchange-inline">isn’t</del> able to indent answers to previous comments if the answer contains multiple lines of Haskell code. Normally, one should (and should be able to) indent answers by preceding <del class="diffchange diffchange-inline">one’s</del> paragraphs with single colons. This <del class="diffchange diffchange-inline">doesn’t</del> really work with haskell tags. <del class="diffchange diffchange-inline">It’s</del> not composable. ;-) </div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>By the way, I <ins class="diffchange diffchange-inline">don't</ins> like that in this wiki one <ins class="diffchange diffchange-inline">isn't</ins> able to indent answers to previous comments if the answer contains multiple lines of Haskell code. Normally, one should (and should be able to) indent answers by preceding <ins class="diffchange diffchange-inline">one's</ins> paragraphs with single colons. This <ins class="diffchange diffchange-inline">doesn't</ins> really work with haskell tags. <ins class="diffchange diffchange-inline">It's</ins> not composable. ;-) </div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>-- [[User:Wolfgang Jeltsch|Wolfgang Jeltsch]] 16:57, 5 December 2007 (UTC)</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>-- [[User:Wolfgang Jeltsch|Wolfgang Jeltsch]] 16:57, 5 December 2007 (UTC)</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>----</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Thanks for catching my <hask>f :$ a</hask> mistake. Do you have a preference about data constructor name, e.g., <hask>App</hask> or <hask>Apply</hask>?</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>I like <hask>(:.)</hask> or <hask>(:.:)</hask> as a replacement for <hask>O</hask>. Hm. I don't remember why I chose <hask>(:*:)</hask> instead of <hask>(:*)</hask>.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Btw, I mean to remove <hask>Id</hask> in favor of the <hask>Id</hask> in Data.Traversable.</div></td>
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Conal
https://wiki.haskell.org/index.php?title=Talk:TypeCompose&diff=17184&oldid=prev
Wolfgang Jeltsch: addition of answer
2007-12-05T16:57:59Z
<p>addition of answer</p>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>----</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Sorry, I hadn’t looked that deeply into TypeCompose to discover App. Yes, this is what I meant.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><hask>(:$)</hask> might be nice as its type constructor name (but not as its data constructor name since the data constructor is unary). But if we use <hask>(:$)</hask> instead of <hask>App</hask>, we should also use <hask>(:.)</hask> instead of <hask>O</hask>. In grapefruit-data, I had a module <hask>Data.Composition</hask> which used <hask>(:.:)</hask>. Actually, I don’t like the <hask>O</hask>. While it looks similar to the function composition operator, it isn’t the function composition operator. Instead, it is just a letter, and identifiers made of letters should be descriptive, in my opinion, like <hask>App</hask>, for example.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>I haven’t played with <hask>(:*:)</hask> and its counterpart yet. No time. :-( </div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Grapefruit now dropped the modules <hask>Data.Monoid.Bonus</hask> and <hask>Data.Composition</hask> and uses TypeCompose&nbsp;0.2 instead.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>By the way, I don’t like that in this wiki one isn’t able to indent answers to previous comments if the answer contains multiple lines of Haskell code. Normally, one should (and should be able to) indent answers by preceding one’s paragraphs with single colons. This doesn’t really work with haskell tags. It’s not composable. ;-) </div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>-- [[User:Wolfgang Jeltsch|Wolfgang Jeltsch]] 16:57, 5 December 2007 (UTC)</div></td>
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Wolfgang Jeltsch
https://wiki.haskell.org/index.php?title=Talk:TypeCompose&diff=17181&oldid=prev
Conal: Reply to Wolfgang -- App
2007-12-04T20:18:29Z
<p>Reply to Wolfgang -- App</p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 20:18, 4 December 2007</td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>I have a type <hask>WrappedApplicative</hask> defined in <hask>Data.Monoid.Bonus</hask> which is part of the [[Grapefruit|grapefruit-data]] package. I introduced it because I wanted to make use of the fact that for every applicative functor a and every monoid m, a m is again a monoid. <hask>Data.Monoid.Bonus</hask> defines an instance <hask>(Applicative a, Monoid m) => Monoid (WrappedApplicative a m)</hask>.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>I have a type <hask>WrappedApplicative</hask> defined in <hask>Data.Monoid.Bonus</hask> which is part of the [[Grapefruit|grapefruit-data]] package. I introduced it because I wanted to make use of the fact that for every applicative functor a and every monoid m, a m is again a monoid. <hask>Data.Monoid.Bonus</hask> defines an instance <hask>(Applicative a, Monoid m) => Monoid (WrappedApplicative a m)</hask>.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td>
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<td class="diff-marker">−</td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Actually, <hask>WrappedApplicative</hask> is just application of a <hask>* -> *</hask> type to a <hask>*</hask> type. So it seems much better to define a <del class="diffchange diffchange-inline">“composition”</del> type which <del class="diffchange diffchange-inline">“composes”</del> a unary type with a nullary type. Such a <del class="diffchange diffchange-inline">“composition”</del> would be an instance of <hask>Monoid</hask> if an applicative functor is composed with a monoid. Thereby I could get rid of <hask>WrappedApplicative</hask>.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Actually, <hask>WrappedApplicative</hask> is just application of a <hask>* -> *</hask> type to a <hask>*</hask> type. So it seems much better to define a <ins class="diffchange diffchange-inline">"composition"</ins> type which <ins class="diffchange diffchange-inline">"composes"</ins> a unary type with a nullary type. Such a <ins class="diffchange diffchange-inline">"composition"</ins> would be an instance of <hask>Monoid</hask> if an applicative functor is composed with a monoid. Thereby I could get rid of <hask>WrappedApplicative</hask>.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Interestingly, <hask>WrappedMonad</hask> is also type application. Maybe the above ideas could also be used to remove <hask>WrappedMonad</hask>. Maybe this would lead us to libraries which <del class="diffchange diffchange-inline">don’t</del> introduce all kinds of wrapper types.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Interestingly, <hask>WrappedMonad</hask> is also type application. Maybe the above ideas could also be used to remove <hask>WrappedMonad</hask>. Maybe this would lead us to libraries which <ins class="diffchange diffchange-inline">don't</ins> introduce all kinds of wrapper types.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>What do you think?</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>What do you think?</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>-- [[User:Wolfgang Jeltsch|Wolfgang Jeltsch]] 18:23, 4 December 2007 (UTC)</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>-- [[User:Wolfgang Jeltsch|Wolfgang Jeltsch]] 18:23, 4 December 2007 (UTC)</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>----</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>I like it. It's the same as <hask>App</hask> in <hask>Control.Compose</hask> in TypeCompose, isn't it?</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><haskell></div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>newtype App f a = App { unApp :: f a }</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>instance (Applicative f, Monoid m) => Monoid (App f m) where</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> mempty = App (pure mempty )</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> App a `mappend` App b = App (liftA2 mappend a b)</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div></haskell></div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>I see this last definition can be improved. I just changed it to the following prettier form (using <hask>inApp2</hask>, defined in <hask>Compose</hask>):</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><haskell></div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>instance (Applicative f, Monoid m) => Monoid (App f m) where</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> mempty = App (pure mempty )</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> mappend = inApp2 (liftA2 mappend)</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div></haskell></div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Maybe a nice infixable name instead of <hask>App</hask>. How about</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><haskell></div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>data f :$ a = f :$ a</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div></haskell></div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>I guess I'd like two infix ops -- one left-associative and one right-associative.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>By the way, have you played with <hask>(:*:)</hask>? It's been terrifically useful for me. Also the binary counterpart, <hask>(:*:)</hask>, e.g., with arrows (and deep arrows). With these tools, Eros can carry around and compose various kinds of info (values, UIs, types, code, pretty-printings, ...), without impacting the code base. Very powerful.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>And yes, I strongly agree with generic names like <hask>App</hask> over more specific-sounding names like<hask>WrappedMonad</hask> and <hask>WrappedApplicative</hask>. I hadn't thought to recommend that kind of change for standard libraries.</div></td>
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Conal
https://wiki.haskell.org/index.php?title=Talk:TypeCompose&diff=17180&oldid=prev
Wolfgang Jeltsch: notes on WrappedApplicative and type composition
2007-12-04T18:23:00Z
<p>notes on WrappedApplicative and type composition</p>
<p><b>New page</b></p><div>Hello Conal,<br />
<br />
I have a type <hask>WrappedApplicative</hask> defined in <hask>Data.Monoid.Bonus</hask> which is part of the [[Grapefruit|grapefruit-data]] package. I introduced it because I wanted to make use of the fact that for every applicative functor a and every monoid m, a m is again a monoid. <hask>Data.Monoid.Bonus</hask> defines an instance <hask>(Applicative a, Monoid m) => Monoid (WrappedApplicative a m)</hask>.<br />
<br />
Actually, <hask>WrappedApplicative</hask> is just application of a <hask>* -> *</hask> type to a <hask>*</hask> type. So it seems much better to define a “composition” type which “composes” a unary type with a nullary type. Such a “composition” would be an instance of <hask>Monoid</hask> if an applicative functor is composed with a monoid. Thereby I could get rid of <hask>WrappedApplicative</hask>.<br />
<br />
Interestingly, <hask>WrappedMonad</hask> is also type application. Maybe the above ideas could also be used to remove <hask>WrappedMonad</hask>. Maybe this would lead us to libraries which don’t introduce all kinds of wrapper types.<br />
<br />
What do you think?<br />
<br />
-- [[User:Wolfgang Jeltsch|Wolfgang Jeltsch]] 18:23, 4 December 2007 (UTC)</div>
Wolfgang Jeltsch