<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
p.Code, li.Code, div.Code
{mso-style-name:Code;
margin-top:0cm;
margin-right:0cm;
margin-bottom:0cm;
margin-left:36.0pt;
margin-bottom:.0001pt;
font-size:9.0pt;
font-family:"Courier New";}
p.msonormal0, li.msonormal0, div.msonormal0
{mso-style-name:msonormal;
mso-margin-top-alt:auto;
margin-right:0cm;
mso-margin-bottom-alt:auto;
margin-left:0cm;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
span.hoenzb
{mso-style-name:hoenzb;}
span.EmailStyle20
{mso-style-type:personal-reply;
font-family:"Calibri",sans-serif;
color:windowtext;
font-weight:normal;
font-style:normal;
text-decoration:none none;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;
mso-fareast-language:EN-US;}
.MsoPapDefault
{mso-style-type:export-only;
margin-top:6.0pt;
margin-right:0cm;
margin-bottom:6.0pt;
margin-left:0cm;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-GB" link="#0563C1" vlink="#954F72">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:12.0pt">Peter<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt">My goal is to determine the type of every expression, pattern etc. in the<br>
syntax tree<span style="font-size:12.0pt"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">After type checking is complete, the syntax tree is liberally annotated with types.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">We do not yet have a function<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"> hsExprType :: HsExpr Id -> Type<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">but we do have<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"> TcHsTyn.hsPatType :: Pat GhcTc -> Type<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">and you or someone could readily make an equivalent for HsExpr.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Most type errors are reported by adding an error constraint, but still returning an annotated tree.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Some, I’m afraid, are still done in the old way, by throwing an exception – so you don’t get back an annotated tree in that case. But they are relatively rare.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Others must have wanted something like this…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<div style="border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt">
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-devs [mailto:ghc-devs-bounces@haskell.org]
<b>On Behalf Of </b>Peter Podlovics<br>
<b>Sent:</b> 02 March 2018 12:05<br>
<b>To:</b> ghc-devs@haskell.org<br>
<b>Subject:</b> Fwd: Type checking expressions<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:12.0pt;margin-left:0cm">
Hello everyone,<br>
<br>
I would like to ask for some advice regarding the type checker part of GHC.<br>
My goal is to determine the type of every expression, pattern etc. in the<br>
syntax tree. Currently the compiler doesn't store this information, so I have<br>
to type check manually. One important aspect is that the program may be ill-typed,<br>
but I still want to extract as much information as possible.<br>
<br>
I tried using local type checking functions (eg.: tcInferSigma), but whenever<br>
I used it on an expression that had some "out-of-scope" names in it, it failed.<br>
<br>
> f xs = length xs<br>
<br>
The reason was that xs was not in the local environment.<br>
<br>
My question is: how could I provide the necessary local environment for these<br>
type checking functions? Also in the general case, is it possible to somehow<br>
annotate each expression with its type during the type checking?<br>
<br>
The motivation for this is that I want to implement a tool that automatically<br>
corrects ill-typed programs based heuristics. For that I need to know the types<br>
of certain AST nodes.<span style="color:#888888"><br>
<br>
<span class="hoenzb">Peter Podlovics</span></span><o:p></o:p></p>
</div>
</div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
<o:p> </o:p></p>
</div>
</div>
</div>
</body>
</html>