> For the complete documentation index, see [llms.txt](https://mind-expression-docs.gitbook.io/home/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mind-expression-docs.gitbook.io/home/how-to-guides/intelligent-process/package-kernel-methods.md).

# Package: Kernel-Methods

## Class: BlockClosure

### Introduction

**Environment: `container`**

* Contains a sequence of operations
* Defined by Mindscript expressions inside square brackets
* Permits to defer the enclosed operations until a variant of #value is executed
* Can have its own arguments and temporaries as a regular method but it also has the ability to use external variables
* It has enclosing method or block temporaries, arguments, and receiver.

Some message needs a code block as argument. For example, `#do:` needs a block to be executed for each element of the receiver.

The block is executed with the element as argument.

```smalltalk
{1. 2. 3. 4. 5. 6. 7. 8. 9. 10} do: [:each | Console print: each, '. '].
```

You can also use a local variable in a block:

```smalltalk
{1. 2. 3. 4. 5. 6. 7. 8. 9. 10} do: [:each |
  | sum |
  sum := 10 + each.
  Console print: sum, '. '].
```

We can also use the block as a local variable, and execute it later by sending `value` to it, or `value:` with an argument.

```smalltalk
aBlock := [ Console print: 'Hello world' ].
"Execute a block"
aBlock value.

"Execute a block with an argument"
aBlock := [:each | Console print: each, '. '].
{1. 2. 3. 4. 5. 6. 7. 8. 9. 10} do: [ :item | aBlock value: item].

```

### Instance Method

#### Category: accessing

* **`asString`** - answer the code string of this block closure.
* **`numArgs`** - answer the number of arguments of the receiver.

#### Category: controlling

* **`whileFalse:`** - Ordinarily compiled in-line, and therefore not overridable. This is in case the message is sent to other than a literal block. Evaluate the argument, aBlock, as long as the value of the receiver is false.

  For example:

  ```smalltalk
  i := 1.
  [ i > 10 ] whileFalse: [ Console print: i, '. '.
    i := i + 1 ].
  ```
* **`whileTrue:`** - Ordinarily compiled in-line, and therefore not overridable. This is in case the message is sent to other than a literal block. Evaluate the argument, aBlock, as long as the value of the receiver is true.

  For example:

  ```smalltalk
  i := 1.
  [ i <= 10 ] whileTrue: [ Console print: i, '. '.
    i := i + 1 ].
  ```

#### Category: evaluating

* **`ensure:`** - Evaluate a termination block after evaluating the receiver, regardless of whether the receiver's evaluation completes.
* **`onErrorDo:`** - Evaluate an error handling block when there is an exception when evaluating the receiver.

  For example, we can use `onErrorDo:` to handle an error when divide by zero.

  ```smalltalk

  a := 1.
  aBlock := [ a := a / 0 ].

  aBlock onErrorDo: [ :ex | a := 0].
  ```
* **`value`** - Evaluate the receiver and answer the result.
* **`value:`** - Evaluate the receiver with the given argument and answer the result.
* **`value:value:`** - Evaluate the receiver with the given arguments and answer the result.
* **`value:value:value:`** - Evaluate the receiver with the given arguments and answer the result.
* **`value:value:value:value:`** - Evaluate the receiver with the given arguments and answer the result.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://mind-expression-docs.gitbook.io/home/how-to-guides/intelligent-process/package-kernel-methods.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.