<div dir="ltr"><div>No, he means that an IO action is just another type. For example you can have a list of IO actions, Then you can take one of them and execute them. Then you can execute that one action again as many times as you want, because an IO action is just a type like any other type until it is executed. These examples are utterly contrived.<br></div><div><br></div>foo :: [IO String]<br>foo = [return "25", print "hello" >> return "qwerty", getLine]<br><br>foo !! 3 :: IO String<br><br>bar :: [IO Int]<br>bar = map (fmap read) foo<br><div><br></div><div>main :: IO ()<br></div>main = do<br> str <- foo !! 2 <br> print str<br> str2 <- foo !! 2<br> print str2<br> i <- head bar<br> print (i + 1)<br><br><div>Even main is just a data structure until the compiler decides to execute it. It could have been written as an expression.</div><div><br></div><div>main = foo !! 2 >>= \str -> print str >> foo !! 2 >>= \str2 -> print str2 >> head bar >>= \i -> print (i + 1)<br><br></div><div><br></div><div><br></div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jul 10, 2018 at 8:29 AM, Olivier Revollat <span dir="ltr"><<a href="mailto:revollat@gmail.com" target="_blank">revollat@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Yes absolutely ! you're referring to laziness right ?</div><div><br></div></div><div class="HOEnZb"><div class="h5"><br><div class="gmail_quote"><div dir="ltr">Le mar. 10 juil. 2018 à 14:20, Theodore Lief Gannon <<a href="mailto:tanuki@gmail.com" target="_blank">tanuki@gmail.com</a>> a écrit :<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto">An intuition that really clicked for me is that in Haskell IO code, as in all Haskell code, you are describing a pristine and perfectly inert data structure. It happens to *represent* a set of imperative instructions that the totally impure runtime environment can execute, but that's not your problem!</div><br><div class="gmail_quote"><div dir="ltr">On Tue, Jul 10, 2018, 4:55 AM Olivier Revollat <<a href="mailto:revollat@gmail.com" target="_blank">revollat@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Thanks ! <br></div><br><div class="gmail_quote"><div dir="ltr">Le mar. 10 juil. 2018 à 13:14, PY <<a href="mailto:aquagnu@gmail.com" rel="noreferrer" target="_blank">aquagnu@gmail.com</a>> a écrit :<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>May be something like this?</p>
<p><b>Free monads</b> ("applicative" style/interpreting trees) and
Effects:</p>
<a class="m_-2448708698946355522m_-7758219068530445940m_699401305901810554m_1124748471038346571moz-txt-link-freetext" href="https://markkarpov.com/post/free-monad-considered-harmful.html" rel="noreferrer" target="_blank">https://markkarpov.com/post/<wbr>free-monad-considered-harmful.<wbr>html</a><br>
<a class="m_-2448708698946355522m_-7758219068530445940m_699401305901810554m_1124748471038346571moz-txt-link-freetext" href="https://mmhaskell.com/blog/2017/11/20/eff-to-the-rescue" rel="noreferrer" target="_blank">https://mmhaskell.com/blog/<wbr>2017/11/20/eff-to-the-rescue</a><br>
<br>
<b>Arrows</b> (something like "flow"-style):<br>
<a class="m_-2448708698946355522m_-7758219068530445940m_699401305901810554m_1124748471038346571moz-txt-link-freetext" href="https://www.haskell.org/arrows/" rel="noreferrer" target="_blank">https://www.haskell.org/<wbr>arrows/</a><br>
<a class="m_-2448708698946355522m_-7758219068530445940m_699401305901810554m_1124748471038346571moz-txt-link-freetext" href="http://tuttlem.github.io/2014/07/26/practical-arrow-usage.html" rel="noreferrer" target="_blank">http://tuttlem.github.io/2014/<wbr>07/26/practical-arrow-usage.<wbr>html</a><br>
<br>
<br>
<div class="m_-2448708698946355522m_-7758219068530445940m_699401305901810554m_1124748471038346571moz-cite-prefix">10.07.2018 12:22, Olivier Revollat
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hi, <br>
I've been using imperative languages for 20 years now :)<br>
<br>
I'm a beginner in haskell and I love the paradigm shift you feel
when you come from imperative programming. I found interesting
articles like :<br>
<a href="https://wiki.haskell.org/Haskell_IO_for_Imperative_Programmers" rel="noreferrer" target="_blank">https://wiki.haskell.org/<wbr>Haskell_IO_for_Imperative_<wbr>Programmers</a><br>
<br>
Do you have any other ressources like that ?<br>
I'm not looking for how to use haskell in imperative style (e.g.
with "do" notation, ...) no no ! I'm looking articles who
explain how NOT TO USE imperative style with haskell, and help
thinking the paradigm shift ...<br>
<br>
Thanks :)<br>
<div><br>
</div>
</div>
<br>
<fieldset class="m_-2448708698946355522m_-7758219068530445940m_699401305901810554m_1124748471038346571mimeAttachmentHeader"></fieldset>
<br>
<pre>______________________________<wbr>_________________
Beginners mailing list
<a class="m_-2448708698946355522m_-7758219068530445940m_699401305901810554m_1124748471038346571moz-txt-link-abbreviated" href="mailto:Beginners@haskell.org" rel="noreferrer" target="_blank">Beginners@haskell.org</a>
<a class="m_-2448708698946355522m_-7758219068530445940m_699401305901810554m_1124748471038346571moz-txt-link-freetext" href="http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners" rel="noreferrer" target="_blank">http://mail.haskell.org/cgi-<wbr>bin/mailman/listinfo/beginners</a>
</pre>
</blockquote>
<br>
</div>
______________________________<wbr>_________________<br>
Beginners mailing list<br>
<a href="mailto:Beginners@haskell.org" rel="noreferrer" target="_blank">Beginners@haskell.org</a><br>
<a href="http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners" rel="noreferrer noreferrer" target="_blank">http://mail.haskell.org/cgi-<wbr>bin/mailman/listinfo/beginners</a><br>
</blockquote></div>
______________________________<wbr>_________________<br>
Beginners mailing list<br>
<a href="mailto:Beginners@haskell.org" rel="noreferrer" target="_blank">Beginners@haskell.org</a><br>
<a href="http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners" rel="noreferrer noreferrer" target="_blank">http://mail.haskell.org/cgi-<wbr>bin/mailman/listinfo/beginners</a><br>
</blockquote></div>
______________________________<wbr>_________________<br>
Beginners mailing list<br>
<a href="mailto:Beginners@haskell.org" target="_blank">Beginners@haskell.org</a><br>
<a href="http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners" rel="noreferrer" target="_blank">http://mail.haskell.org/cgi-<wbr>bin/mailman/listinfo/beginners</a><br>
</blockquote></div>
</div></div><br>______________________________<wbr>_________________<br>
Beginners mailing list<br>
<a href="mailto:Beginners@haskell.org">Beginners@haskell.org</a><br>
<a href="http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners" rel="noreferrer" target="_blank">http://mail.haskell.org/cgi-<wbr>bin/mailman/listinfo/beginners</a><br>
<br></blockquote></div><br></div>