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# 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.