<div dir="ltr"><div>I know there was a bug in the parser related to setting the HsBang value, it could be that this whole area has just not received solid scrutiny before now.<br><br></div>Alan<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Jan 8, 2015 at 10:15 AM, Johan Tibell <span dir="ltr"><<a href="mailto:johan.tibell@gmail.com" target="_blank">johan.tibell@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">I also note that the definition of isBanged is confusing:<span class=""><div><br></div><div><div style="font-size:13px">  isBanged :: HsBang -> Bool</div><div style="font-size:13px">  isBanged HsNoBang          = False</div><div style="font-size:13px">  isBanged (HsUserBang Nothing bang) = bang</div><div style="font-size:13px">  isBanged _             = True</div></div><div style="font-size:13px"><br></div></span><div style="font-size:13px">Why is `HsUserBang (Just False) False`, corresponding to a NOUNPACK annotations with a missing "!", considered "banged"?</div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Jan 8, 2015 at 8:36 AM, Johan Tibell <span dir="ltr"><<a href="mailto:johan.tibell@gmail.com" target="_blank">johan.tibell@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">HsBang is defined as:<br><br><div>  -- HsBang describes what the *programmer* wrote</div><div>  -- This info is retained in the DataCon.dcStrictMarks field</div><div>  data HsBang</div><div>   = HsUserBang  -- The user's source-code request</div><div>      (Maybe Bool)    -- Just True   {-# UNPACK #-}</div><div>               -- Just False  {-# NOUNPACK #-}</div><div>               -- Nothing    no pragma</div><div>      Bool        -- True <=> '!' specified</div><div><br></div><div>   | HsNoBang        -- Lazy field</div><div>               -- HsUserBang Nothing False means the same as HsNoBang</div><div><br></div><div>   | HsUnpack        -- Definite commitment: this field is strict and unboxed</div><div>      (Maybe Coercion)  --   co :: arg-ty ~ product-ty</div><div><br></div><div>   | HsStrict        -- Definite commitment: this field is strict but not unboxed</div><br>This data type is a bit unclear to me:<br><br> * What are the reasons for the following constructor overlaps?<br>  * `HsNoBang` and `HsUserBang Nothing False`<br>  * `HsStrict` and `HsUserBang Nothing True`<br>  * `HsUnpack mb_co` and `HsUserBang (Just True) True`<div><br>* Why is there a coercion in `HsUnpack` but not in `HsUserBang (Just True) True`?</div><div><br><div>* Is there a difference in what the user wrote in the case of HsUserBang and HsNoBang/HsUnpack/HsStrict e.g are the latter three generated by the compiler as opposed to being written by the user (the function documentation notwithstanding)?<br><br>A very related function is isBanged:<br><br><div>  isBanged :: HsBang -> Bool</div><div>  isBanged HsNoBang          = False</div><div>  isBanged (HsUserBang Nothing bang) = bang</div><div>  isBanged _             = True</div><div><br></div><div>What's the meaning of this function? Is it intended to communicate what the user wrote or whether result of what the user wrote results in a strict function?</div><br>Context: I'm adding a new StrictData language pragma [1] that makes fields strict by default and a '~' annotation of fields to reverse the default behavior. My intention is to change HsBang like so:<br><br>  -    Bool        -- True <=> '!' specified<br>  +    (Maybe Bool)    -- True <=> '!' specified, False <=> '~'<br>  +              -- specified, Nothing <=> unspecified<br><br>1. <a href="https://ghc.haskell.org/trac/ghc/wiki/StrictPragma" target="_blank">https://ghc.haskell.org/trac/ghc/wiki/StrictPragma</a></div><span><font color="#888888"><div><br>-- Johan<br></div></font></span></div></div>
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