MSDN Magazine - October 2007 - (Page 22)

first node under the body node to actually see the BlockStatement’s contents. This DLR BlockStatement AST node corresponds to the IronPython AST’s SuiteStatement node, and each represents a series of statements. Expand the statements property. The first statement (index 0) is an EmptyStatement, which is an artifact of IronPython’s translation to the DLR tree. IronPython allocates two statements in case there’s a module documenta- tion string, which would cause the creation of an assignment to __doc In this case the first statement remains as a placeholder EmptyStatement since there’s no documentation string. The second statement (index 1) is what’s interesting because it is the BlockStatement for the rest of the file, which is the code I wrote. This BlockStatement contains an ExpressionStatement followed by a BlockStatement (discussed later). The ExpressionStatement node wraps a BoundAssignment node so that the resulting value of the assignCodeBlock ment gets popped off the stack; Python Variables: [0] Local {_name_} assignments do not return values. The [1] Local {yo} Body: BlockStatement BoundAssignment has name and value members. They represent setting the local variable yo (local to the module the BlockStatement Python code executes in) to the result of a function call. The function call, represented by a MethodCallExpression, ExpressionStatement ExpressionStatement calls a runtime helper function that Expression: BoundAssignment Expression: BoundAssignment creates an IronPython function object. MethodCallExpression has members indicating that the call is to a method MethodCallExpression BoundAssignment named MakeFunction and what arguMethod: {RuntimeMethodInfo Variable: {Kind: Local, Name {yo}} ments the call gets. One argument is a {Name: “Print”}} Value: MethodCallExpression CodeBlockExpression AST node for Arguments: [0] ActionExpression the function’s body, and another is an array of parameters the created funcMethodCallExpression ActionExpression tion will take. (yo(“bill”)) Method: {RuntimeMethodInfo Expand the MethodCallExpression {Name: “MakeFunction”} Action: CallAction: AST node, which is the value mem{ReturnType: PythonFunction}} Arguments: [0] {BoundExpression Arguments: , CodeBlockExpression, ber of the BoundAssignment. Look {Variable: Local {yo}}} at the third element (index 2) of the [1] {ConstantExpression {“bill”}} Arguments property, you’ll see the CodeBlockExpression CodeBlockExpression for the body of yo. It has a Block property that is a CodeBlock. The CodeBlockExpression BlockStatement CodeBlock causes the CodeBlock it wraps to turn (def yo (): ) into a callable value that can be assigned Name: yo to a module variable. Before we go into ExpressionStatement ReturnStatement Body: BlockStatement Parameters: [0] Parameter {yourname} the body of the yo function’s AST, look Expression: BoundAssignment Variables: [0] Local {text} at Figure 4, which is a diagram of the entire DLR AST for msdnmag.py. There are a couple of notes about BoundAssignment the diagram. As with the previous dia(text = “hello, ”) gram, there is a mixture of visual repValue: ConstantExpression {“hello, ”} resentation in the tree. For the most Variable: Local {text} part, if an AST node has a member that points to another AST node, the ActionExpression (text + yourname) picture shows an arrow pointing to the subnode. Sometimes a node contains Action: DoOperationAction {Add} Arguments: [0] {BoundExpression a description of the subnodes using {Variable: Local {text}}} indentation and curly braces instead [1] {BoundExpression of more arrows and boxes. The snap{Variable: Parameter {yourname}}} shot of the Locals window in Visual Studio shows the AST down to the Figure 4 Entire DLR AST for msdnmag.py 22 msdnmagazine CLR Inside Out

Table of Contents Feed for the Digital Edition of MSDN Magazine - October 2007

Cover Contents Toolbox CLR Inside Out Basic Instincts Data Points Cutting Edge Pooled Threads WPF Threads Parallel Linq Parallel Performance Mobile Apps Test Run Foundations Windows with C++ Netting C++ .NET Matters { End Bracket } Net Nuptials

MSDN Magazine - October 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.