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semantic_tutorial [2015/11/09 21:31]
deva [Step 5: Type checking]
semantic_tutorial [2016/12/01 17:07]
deva
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 ==== Step 1: Preparation === ==== Step 1: Preparation ===
  
-  * In this tutorial we use the [[http://​deva.web.elte.hu/​compilers/​lab/​while-language.html|While language]]. It is possible to use your own lexer and parser. If you have not completed it, use [[http://​deva.web.elte.hu/​compilers/lab/​parser.zip|this implementation]].+  * In this tutorial we use the [[http://​deva.web.elte.hu/​compilers/​lab/​while-language.html|While language]]. It is possible to use your own lexer and parser. If you have not completed it, use [[http://​deva.web.elte.hu/​compilers/​parser.zip|this implementation]].
   * If you are working not with your own parser, please take the time to understand the grammar.   * If you are working not with your own parser, please take the time to understand the grammar.
   * Look into the ''​Parser.ih''​ file.   * Look into the ''​Parser.ih''​ file.
     * The function called ''​lex''​ asks the current line number from the parser and saves it into a field of the ''​d_loc<​nowiki>​__</​nowiki>''​ attribute of the ''​Parser''​ class. Then it asks for the next token from the lexer and returns it to the parser.     * The function called ''​lex''​ asks the current line number from the parser and saves it into a field of the ''​d_loc<​nowiki>​__</​nowiki>''​ attribute of the ''​Parser''​ class. Then it asks for the next token from the lexer and returns it to the parser.
     * The line number information is used in the ''​error''​ function to print location information for error messages.     * The line number information is used in the ''​error''​ function to print location information for error messages.
-  * Make sure you can compile the parser and it accepts all the correct [[http://​deva.web.elte.hu/​compilers/lab/​while-tests.zip|test files]] and rejects the lexical error ones. Try out the semantic error test cases! They are accepted. The goal of the tutorial is to find those errors as well.+  * Make sure you can compile the parser and it accepts all the correct [[http://​deva.web.elte.hu/​compilers/​while-tests.zip|test files]] and rejects the lexical error ones. Try out the semantic error test cases! They are accepted. The goal of the tutorial is to find those errors as well.
  
 ==== Step 2: Symbol table === ==== Step 2: Symbol table ===
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   * Find out how is the non-terminal symbol for expressions is called in your grammar. (It is ''​expression''​ in the parser downloadable at the beginning of this tutorial, but it might have a different name in your own solution.) Since this is a non-terminal,​ you can define the type of its semantic value as follows. (Insert it near the token declarations at the beginning of ''​while.y''​.)   * Find out how is the non-terminal symbol for expressions is called in your grammar. (It is ''​expression''​ in the parser downloadable at the beginning of this tutorial, but it might have a different name in your own solution.) Since this is a non-terminal,​ you can define the type of its semantic value as follows. (Insert it near the token declarations at the beginning of ''​while.y''​.)
 <​code>​ <​code>​
-%type expr_type expression+%type <expr_typeexpression
 </​code>​ </​code>​
   * For each //​expression rule//, do the necessary type checking and set the semantic value of the left-hand side of the rule. The semantic value of the left-hand side can be referenced by the ''​$$''​ symbol.   * For each //​expression rule//, do the necessary type checking and set the semantic value of the left-hand side of the rule. The semantic value of the left-hand side can be referenced by the ''​$$''​ symbol.
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     * In case of expressions build using operators, there is need for type checking the arguments. For example, the rule for addition will have this C++ code:     * In case of expressions build using operators, there is need for type checking the arguments. For example, the rule for addition will have this C++ code:
 <​code>​ <​code>​
-if($1->​expr_type ​!= integer || $3->​expr_type ​!= integer)+if(*$1 != integer || *$3 != integer)
 { {
    ​std::​stringstream ss;    ​std::​stringstream ss;
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 ==== Step 6: Fixing the memory leaks ==== ==== Step 6: Fixing the memory leaks ====
 +
 +All the semantic values were created using the ''​new''​ keyword of C++. This means we have to delete them in order to avoid memory leakage.
 +  * Review all the rules and delete the semantic values of the symbols on the right-hand side at the end of the corresponding C++ code fragments (change ''​i''​ to the appropriate number):
 +<​code>​
 +delete $i;
 +</​code>​
 +
semantic_tutorial.txt · Last modified: 2016/12/08 13:25 by deva