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diff --git a/chapter03/README.md b/chapter03/README.md index 31f3d46a..3e6cebfe 100644 --- a/chapter03/README.md +++ b/chapter03/README.md @@ -17,7 +17,7 @@ Here is the [complete language grammar](docs/03-grammar.md) for this chapter. ## Extensions to Intermediate Representation -In this chapter we do not add new nodes. To recap, our list of Nodes are: +To recap, our list of Nodes are: | Node Name | Type | Description | Inputs | Value | |------------|---------|------------------------------------|------------------------------------------------------------------|-------------------------------------------------------| @@ -30,6 +30,13 @@ In this chapter we do not add new nodes. To recap, our list of Nodes are: | Div | Data | Divide a value by another | Two data nodes, values are divided, order matters | Result of the division | | UnaryMinus | Data | Negate a value | One data node, value is negated | Result of the unary minus | +In this chapter we introduce: + +| Node Name | Type | Description | Inputs | Value | +|-----------|------|--------------------------------|---------------------------------|-------| +| Scope | ? | Represents scopes in the graph | All nodes that define variables | None | + + ## Symbol Tables To support variable declarations and lexical scopes, we introduce symbol tables in the parser. @@ -42,6 +49,19 @@ Declaring a name adds it to the current symbol table. If a name is assigned to, then its mapping in the most recent symbol table is updated. If a name is accessed, its mapping is looked up in the symbol tables. The lookup goes up the stack of symbol tables. +## ScopeNode + +We wrap the stack of symbol tables in a `ScopeNode`. When a name binding is added to a symbol table, +we also make the newly added node an input in the `ScopeNode`. This means that the `ScopeNode` is a user of +all nodes that define new names. + +From an implementation point of view, the symbol table maps names to offsets in the ScopeNode's inputs. + +When a scope is exited, we not only pop the symbol table representing the scope, but also remove the relevant input nodes. + +In the visualization, we show the ScopeNode in a separate box; the stack of symbol tables is shown inside +the box. We show the edge from each variable in the symbol table to the defining Node in the graph. + ## Demonstration We show the output from following code. @@ -68,7 +88,7 @@ see the graph as its initially constructed).  -The diagram shows the symbol tables in the bottom cluster. +The diagram shows the ScopeNode and the symbol tables in the bottom cluster. Each table is annotated by its scope level, and shows the variables defined in that scope. * When we exit the nested scope on line 8, the symbol table at level 1 is popped. |