> For the complete documentation index, see [llms.txt](https://docs.yarnspinner.dev/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.yarnspinner.dev/3.1/api/csharp/yarn.compiler/yarn.compiler.functiontypebuilder/yarn.compiler.functiontypebuilder.withparameter.md).

# WithParameter(IType)

Method in [FunctionTypeBuilder](/3.1/api/csharp/yarn.compiler/yarn.compiler.functiontypebuilder.md)

## Summary

Adds a new parameter of type `parameterType` to the [FunctionType](/3.1/api/csharp/yarn.compiler/yarn.compiler.functiontypebuilder/yarn.compiler.functiontypebuilder.functiontype.md) .

```csharp
public FunctionTypeBuilder WithParameter(IType parameterType)
```

## Parameters

| Name                                                           | Description                                           |
| -------------------------------------------------------------- | ----------------------------------------------------- |
| [Yarn.IType](/3.1/api/csharp/yarn/yarn.itype.md) parameterType | The type of the new parameter to add to the function. |

## Returns

The [FunctionTypeBuilder](/3.1/api/csharp/yarn.compiler/yarn.compiler.functiontypebuilder.md) instance that received this method call.