<div dir="ltr">You can't use guards in record syntax, but you could use `case` here instead of `let`, or just write a function of type `String -> BuyOrSell` and use that.</div><div class="gmail_extra"><br><br><div class="gmail_quote">
On Sun, Apr 13, 2014 at 11:03 PM, Dimitri DeFigueiredo <span dir="ltr"><<a href="mailto:defigueiredo@ucdavis.edu" target="_blank">defigueiredo@ucdavis.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
I'm having some trouble understanding where I can or cannot use guards inside record syntax. I'm writing a simple conversion routine, but I am not able to write it without inserting an extra let. Do I need a let expression here? Am I missing something?<br>
<br>
--------------<br>
data OldTrade = OldTrade {<br>
oldprice :: Double ,<br>
oldamount :: Double ,<br>
oldbuysell :: String -- "buy", "sell" or ""<br>
} deriving( Eq, Show)<br>
<br>
<br>
data BuyOrSell = Buy | Sell | Unknown deriving(Eq, Show)<br>
<br>
data Trade = Trade {<br>
price :: Double ,<br>
amount :: Double ,<br>
buysell :: BuyOrSell<br>
} deriving( Eq, Show)<br>
<br>
convert :: OldTrade -> Trade<br>
<br>
convert ot = Trade { price = oldprice ot,<br>
amount = oldamount ot,<br>
buysell = let x | oldbuysell ot == "buy" = Buy<br>
| oldbuysell ot == "sell" = Sell<br>
| otherwise = Unknown<br>
in x<br>
}<br>
<br>
-- how do I eliminate the 'let' expression here?<br>
-- I wanted to write something like:<br>
--<br>
-- buysell | oldbuysell ot == "buy" = Buy<br>
-- | oldbuysell ot == "sell" = Sell<br>
-- | otherwise = Unknown<br>
<br>
--------------<br>
<br>
Thanks!<br>
<br>
Dimitri<br>
<br>
<br>
<br>
<br>
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</blockquote></div><br></div>