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# Chapter 5
In this chapter we extend the language grammar with following features:
* We introduce the `if` statement.
* To support splitting of control flow and merging, we introduce new nodes: `Region` and `Phi`.
* Since we can now have multiple return points, we also introduce the `Stop` node as the termination.
Here is the [complete language grammar](docs/05-grammar.md) for this chapter.
## Recap
Here is a recap of the nodes introduced in previous chapters:
| Node Name | Type | Chapter | Description | Inputs | Value |
|------------|----------------|---------|------------------------------------------------|------------------------------------------------------------------|-------------------------------------------------------------------------|
| MultiNode | Abstract class | 4 | A node that has a tuple result | | A tuple |
| Start | Control | 1 | Start of function, now a MultiNode | An input argument named `arg`. | A tuple with a ctrl token and an `arg` data node |
| Proj | ? | 4 | Projection nodes extract values from MultiNode | A MultiNode and index | Result is the extracted value from the input MultiNode at offset index |
| Bool | Data | 4 | Represents results of a comparison operator | Two data nodes | Result a comparison, represented as integer value where 1=true, 0=false |
| Return | Control | 1 | End of function | Predecessor control node, Data node value | Return value of the function |
| Constant | Data | 1 | Constants such as integer literals | None, however Start node is set as input to enable graph walking | Value of the constant |
| Add | Data | 2 | Add two values | Two data nodes, values are added, order not important | Result of the add operation |
| Sub | Data | 2 | Subtract a value from another | Two data nodes, values are subtracted, order matters | Result of the subtract |
| Mul | Data | 2 | Multiply two values | Two data nodes, values are multiplied, order not important | Result of the multiply |
| Div | Data | 2 | Divide a value by another | Two data nodes, values are divided, order matters | Result of the division |
| UnaryMinus | Data | 2 | Negate a value | One data node, value is negated | Result of the unary minus |
| Scope | ? | 3 | Represents scopes in the graph | All nodes that define variables | None |
## New Nodes
Following new nodes are introduced in this chapter:
| Node Name | Type | Chapter | Description | Inputs | Value |
|-----------|---------|---------|----------------------------------------------------------------------|------------------------------------------------------------------------------------------------|---------------------------------------------------------------|
| If | Control | 5 | Represents an `if` condition, sub type of `MultiNode` | A control node and a data predicate node | A tuple of two values, one for true branch, another for false |
| Region | Control | 5 | Represents a merge point from multiple control flow | An input for each control flow that is merging | None |
| Phi | ? | 5 | Represents the phi function that picks a value based on control flow | A region control node, and multiple data nodes that provide values from multiple control flows | Result is the extracted value depending on control flow taken |
| Stop | Control | 5 | Represents termination of the program | One or more Return nodes | None |
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