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semantic_tutorial
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semantic_tutorial [2015/11/09 21:31] deva [Step 5: Type checking] |
semantic_tutorial [2015/11/20 16:01] deva |
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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_type> expression |
| </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. | ||
| Line 118: | Line 118: | ||
| * 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; | ||
| Line 130: | Line 130: | ||
| ==== 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
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