型システムのデバッグ

For debugging typesystem MPS provides Typesystem Trace - an integrated visual tool that gives you insight into the evaluation process that happens inside the typesystem engine.

Try it out for yourself

We prepared a dedicated sample language for you to easily experiment with the typesystem. Open the 式 sample project that comes bundled with MPS and should be available among the sample projects in the user home folder.

The sample language

The language to experiment with is a simplified expression language with several types, four arithmetic operations (+, -, *, /), assignment (:=), two types of variable declarations and a variable reference. The editor is very basic with almost no customization, so editing the expressions will perhaps be quite rough. Nevertheless, we expect you to inspect the existing samples and debug their types more than writing new code, so the lack of smooth editing should not be an issue.

The expression language supports six types, organized by subtyping rules into two branches:

1. Element -> Number -> Float -> Long -> Int

2. Element -> Bool

Inspecting the types

If you open the シンプル example class, you can position the cursor to any part of the expression or select a valid expression block. As soon as you hit Control/Cmd +Shift + T , you'll see the type of the selected node in a pop-up dialog.

Type errors

The TypeError sample class shows a simple example of a type error. Just uncomment the code ( Control/Cmd + / ) and check the reported error:

Since this variable declaration declares its type explicitly to be an Int , while the initializer is of type 浮く , the type-system reports an error. You may check the status bar at the bottom or hover your mouse over the incorrect piece of code.

型システムトレース

When you hit Control/Cmd + Shift + X or navigate through the pop-up menu, you get the Typesystem Trace panel displayed on the right hand-side.

Step-by-step debugging

The シンプル sample class is probably the easiest one to start experimenting with. The types get resolved in six steps, following the typesystem rules specified in the language. You may want to refer to these rules quickly by pressing F4 _or using the _Control/Cmd + N "Go to Root Node" command. F3 will navigate you to the node, which is being affected by the current rule.

1. The type of a variable declaration has to be a super-type of the type of the initializer. The aValue variable is assigned the a type-system variable, the initializer expression is assigned the b type-system variable and a>=b (b sub-type or equal type to a) is added into the working memory.

2. Following the type-system rule for Arithmetic Expressions, b has to be a sub-type of 番号 , the value 10 is assigned the c variable, 1.3F is assigned the d variable and a when-concrete handler is added to wait for c to be calculated.

3. Following the rules for float constants d is solved as 浮く .

4. Following the rules for integer constants c is solved as Int . This triggers the when-concrete handler registered in step 2 and registered another when-concrete handler to wait for d . Since d has already been resolved to 浮く , the handler triggered and resolves b (the whole arithmetic expression) as 浮く . This also solves the earlier equation (step 2) that b<=Number .

5. Now a can be resolved as 浮く , which also solves the step 1 equation that a>=b .

6. If you enable type expansions by pressing the button in the tool-bar, you'll get the final expansions of all nodes to concrete types as the last step.

関連ページ：

Using_typesystem

型システムを使う言語の型システムを定義した場合、タイプチェッカーは自動的にそれをエディターで使用して、開いているノードをエラーと警告で強調表示します。また、エディターアクションやジェネレータクエリなど、クエリの型に関する情報を使用することもできます。ノードの型を使用することも、特定の型が別の型のサブ...