imported>Andy |
imported>Mathieu |
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| − | = Defining Translations Using The Theory Plug-in =
| + | Import from original Rodin user manual - Overwriting bad images previsouly uploaded |
| − | The theory plug-in is used to add mathematical extensions to Rodin. The theories are created, and deployed, and can then be used in any models in the workspace. When dealing with implementation level models, such as in Tasking Event-B, we need to consider how to translate newly added types and operators into code. We have augmented the theory interface with a Translation Rules section. This enables a user to define translation rules that map Event-B formulas to code.
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| − | == Translation Rules==
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| − | <div id="fig:Translation Rules">
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| − | <br/>
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| − | [[Image:TheoryCGRules.png|center||caption text]]
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| − | <center>'''Figure 1''': Translation Rules</center>
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| − | <br/>
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| − | </div>
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| − | Figure 1 shows the interface, and some translations rules of the mapping to Ada.
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| − | The theory is given a name, and may import some other theories. Type parameters can be added, and we use them here to type the meta-variables. The meta-variable ''a'' is restricted to be an integer type, but meta-variable ''c'' can be any type. Meta-variables are used in the translator rules for pattern matching.
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| − | Translator rules are templates, which are used in pattern matching. Event-B expressions and predicates are defined on the left hand side of the rule, and the code to be output (as text) appears on the right hand side of the matching rule. During translation an abstract syntax tree (AST) of the source string is constructed. The theory plug-in then attempts to match the rules with each syntactic element of the AST. As it does so it builds the code to output, until the whole AST has been successfully matched. When a complete tree is matched the target code is returned. If the AST is not matched, a warning is issued, and the original string is returned.
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| − | == Type Rules for Code Generation ==
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| − | The type rules section, shown in Figure 1, is where the relationship is defined, between Event-B types and the type system of the implementation.
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| − | = Adding New (implementation-level) Types =
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| − | When we are working at abstraction levels close to the implementation level, we may make an implementation decision which requires the introduction of a new type to the development. We give an example of our approach, where we add a new array type, shown in Figure 2, and then define its translation to code.
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| − | == An Array Type Definition ==
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| − | <div id="fig:Extension with an Array Type">
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| − | <br/>
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| − | [[Image:ArrayDef.png|center||caption text]]
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| − | <center>'''Figure 2''': Array Definition</center>
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| − | <br/>
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| − | </div>
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| − | The array operator notation is defined in the expression array(s: P(T)); and the semantics is defined in the direct definition. arrayN constrains the arrays to be of fixed length. Array lookup, update, and constructor operators are subsequently defined. In the next step we need to define any translations required to implement the array in code.
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| − | == Translation Rules ==
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| − | <div id="Translation Rules for the Array Type">
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| − | <br/>
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| − | [[Image:ArrayTrans.png|center||caption text]]
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| − | <center>'''Figure 3''': Translation Rules for the Array Type</center>
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| − | <br/>
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| − | </div>
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| − | Figure 3 shows the Ada translation; beginning with the meta-variable definitions that are used for pattern matching in the translation rules. Each of the operators; ''newArray'', and ''update'', and an expression using the ''lookup'' operator, are mapped to their implementations on the right hand side of the rule. The ''Type Rules'' section describes the implementation's description of the ''arrayN'' type.
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