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Analyzing the ParseResult of haskell-src-extensions
17 Apr 2015
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#haskell haskell-src-extensions parse-result
#haskell
The project I have proposed requires to analyze the source code in order to query the declared function matching certain conditions. Haskell-Src-Extensions has a parser in which we can get a data type which contains information about (the Module in) a Haskell (.hs) file. The porpose of this post is to analyze together the ParseResult of a Haskell (.hs) file. I have created two files that you could find here.
<ul><li style="margin-bottom: 0in; line-height: 100%;">
<strong>Main.hs:</strong> the parser.</li>
<li style="margin-bottom: 0in; line-height: 100%;">
<strong>Tutorial.hs: </strong>the file we are going to analyze.</li>
</ul><p style="margin-bottom: 0in; line-height: 100%;">
We compile the program by doing</p>
<pre> ghc -package ghc Main.hs</pre>
<p>
</p>
<p style="margin-bottom: 0in; line-height: 100%;">
If we execute the program by doing</p>
<pre> ./Main.hs Tutorial.hs</pre>
<p style="margin-bottom: 0in; line-height: 100%">
The result will be the representation of a Module data type, which we can see in the following line:</p>
<pre> <strong>Module</strong> <span style="background-color:#afeeee;">(SrcLoc "Tutorial.hs" 1 1)</span><span style="background-color:#dda0dd;"> (ModuleName "Tutorial")</span> <span style="background-color:#00ff00;">[]</span> <span style="background-color:#ffd700;">Nothing</span> <span style="background-color:#ff8c00;">(Just [])</span> <span style="background-color:#ffa07a;">[]</span> <span style="background-color:#696969;">[TypeSig (SrcLoc "Tutorial.hs" 3 1) [Ident "fib"] (TyFun (TyCon (UnQual (Ident "Integer"))) (TyCon (UnQual (Ident "Integer")))),FunBind [Match (SrcLoc "Tutorial.hs" 4 1) (Ident "fib") [PLit Signless (Int 0)] Nothing (UnGuardedRhs (Lit (Int 0))) (BDecls []),Match (SrcLoc "Tutorial.hs" 5 1) (Ident "fib") [PLit Signless (Int 1)] Nothing (UnGuardedRhs (Lit (Int 1))) (BDecls []),Match (SrcLoc "Tutorial.hs" 6 1) (Ident "fib") [PVar (Ident "n")] Nothing (UnGuardedRhs (InfixApp (App (Var (UnQual (Ident "fib"))) (Paren (InfixApp (Var (UnQual (Ident "n"))) (QVarOp (UnQual (Symbol "-"))) (Lit (Int 1))))) (QVarOp (UnQual (Symbol "+"))) (App (Var (UnQual (Ident "fib"))) (Paren (InfixApp (Var (UnQual (Ident "n"))) (QVarOp (UnQual (Symbol "-"))) (Lit (Int 2))))))) (BDecls [])]]</span></pre>
<p style="margin-bottom: 0in; line-height: 100%">
If we look at the declaration of the Module data type, we can see that it is:</p>
<pre> <strong>Module</strong> <span style="background-color:#afeeee;">SrcLoc</span> <span style="background-color:#dda0dd;">ModuleName</span> <span style="background-color:#00ff00;">[ModulePragma]</span> <span style="background-color:#ffd700;">(Maybe WarningText)</span> <span style="background-color:#ff8c00;">(Maybe [ExportSpec])</span> <span style="background-color:#ffa07a;">[ImportDecl]</span> <span style="background-color:#696969;">[Decl]</span></pre>
<p style="margin-bottom: 0in; line-height: 100%">
The definition is colored, so you can difference easily between the parameters. The <span style="background-color:#00ff00;">[ModulePragma]</span>, the <span style="background-color:#ffd700;">MaybeWarningText</span>, the <span style="background-color:#ff8c00;">(Maybe [ExportSpec])</span> and <span style="background-color:#ffa07a;">[ImportDecl]</span> doesn’t have relevant information. But in the <span style="background-color:#696969;">[Decl]</span> parameter we have many information. We will make a “zoom” here.</p>
<p style="margin-bottom: 0in; line-height: 100%; text-align: center;">
<br/>
…</p>
<p style="margin-bottom: 0in; line-height: 100%">
<br/><em>Note: Forget colors above. Now we use different colors.</em></p>
<pre> [<span style="background-color:#40e0d0;">TypeSig (SrcLoc "Tutorial.hs" 3 1) [Ident "fib"] (TyFun (TyCon (UnQual (Ident "Integer"))) (TyCon (UnQual (Ident "Integer"))))</span>,<span style="background-color:#dda0dd;">FunBind [Match (SrcLoc "Tutorial.hs" 4 1) (Ident "fib") [PLit Signless (Int 0)] Nothing (UnGuardedRhs (Lit (Int 0))) (BDecls [])</span>,<span style="background-color:#ffff00;">Match (SrcLoc "Tutorial.hs" 5 1) (Ident "fib") [PLit Signless (Int 1)] Nothing (UnGuardedRhs (Lit (Int 1))) (BDecls [])</span>,<span style="background-color:#ffa07a;">Match (SrcLoc "Tutorial.hs" 6 1) (Ident "fib") [PVar (Ident "n")] Nothing (UnGuardedRhs (InfixApp (App (Var (UnQual (Ident "fib"))) (Paren (InfixApp (Var (UnQual (Ident "n"))) (QVarOp (UnQual (Symbol "-"))) (Lit (Int 1))))) (QVarOp (UnQual (Symbol "+"))) (App (Var (UnQual (Ident "fib"))) (Paren (InfixApp (Var (UnQual (Ident "n"))) (QVarOp (UnQual (Symbol "-"))) (Lit (Int 2))))))) (BDecls [])]</span>]</pre>
<p style="margin-bottom: 0in; line-height: 100%">
This element is a list of declarations (<strong>[Decl]</strong>). Each element of this list, could represent the declaration of a type, a data type or a signature or a function, etc. In this case, the following declarations matches with:</p>
<pre> <span style="background-color:#40e0d0;">fib :: Integer -> Integer</span> <span style="background-color:#ee82ee;">fib 0 = 0</span> <span style="background-color:#ffff00;">fib 1 = 1</span> <span style="background-color:#ffa07a;">fib n = fib (n - 1) + fib (n - 2)</span></pre>
<p>
<strong>1. The first element (<span style="background-color:#40e0d0;">-</span>):</strong><br/>
It represents a signature. TypeSig ‘contents’ the following elements:</p>
<ul><li>
<em><strong>SrcLoc: </strong></em>the filepath of the source file.</li>
<li>
<em><strong>[Ident …]:</strong></em> the name of the signature or function</li>
<li>
<em><strong>TyFun:</strong></em> says that this signature <strong>returns an Integer </strong>data type and <strong>receives an Integer</strong> data type, <strong>in this order.</strong></li>
</ul><p>
<strong>2. The second element of the list (<span style="background-color:#ee82ee;">-</span><span style="background-color:#ffff00;">-</span><span style="background-color:#ffa07a;">-</span>):</strong><br/>
It represents the declaration of a function, in this case “fib”. FunBind contents a list of Match which contents the following values:<br/><strong>2.1 First subelement</strong>, it makes reference to “fib 0 = 0”.</p>
<ul><li>
<em><strong>SrcLoc: </strong></em>the filepath of the source file.</li>
<li>
<em><strong>Ident …:</strong></em> the name of the function</li>
<li>
<em><strong>[PLit Signless (Int 0)]</strong></em>: the pattern, in this case is literal (constant) and it is 0.</li>
<li>
<em><strong>Nothing</strong></em></li>
<li>
<em><strong>(UnGuardedRhs (Lit (Int 1)))</strong>: </em>this is the content in the body of the function, in this case it is only 1.</li>
<li>
<em><strong>BDecls []: </strong></em>these are the declarations inside the function, for example, in where clauses (or in let clauses, too?)</li>
</ul><p>
<strong>2.2 Second subelement</strong>, it is pretty similar to 2.1, but parsing “fib 1 = 1”</p>
<p>
<strong>2.1 Third subelement</strong>, it makes reference to “fib 0 = 0”.</p>
<ul><li>
<em><strong>SrcLoc: </strong></em>the filepath of the source file.</li>
<li>
<em><strong>Ident …:</strong></em> the name of the function</li>
<li>
<em><strong>[PVar (Ident “n”)]:</strong></em> in this case the pattern is a variable and it is n.</li>
<li>
<em><strong>Nothing</strong></em></li>
<li>
<em><strong>(UnGuardedRhs (InfixApp (App (Var (UnQual (Ident “fib”))) (Paren (InfixApp (Var (UnQual (Ident “n”))) (QVarOp (UnQual (Symbol “-”))) (Lit (Int 1))))) (QVarOp (UnQual (Symbol “+”))) (App (Var (UnQual (Ident “fib”))) (Paren (InfixApp (Var (UnQual (Ident “n”))) (QVarOp (UnQual (Symbol “-”))) (Lit (Int 2))))))):</strong></em>
here we can see that it is parsing the part of “fib (n - 1) + fib (n - 2)”</li>
<li>
<em><strong>BDecls []: </strong></em>these are the declarations inside the function, for example, in where clauses.</li>
</ul>
Fabián Orccón is an awesome person. He lives in Perú, the land of the Incas.