# MEANS

Introduces the body of a function or decision. Connects a function name to its definition.

## Syntax

```l4
name MEANS expression
DECIDE name MEANS expression
```

## Purpose

MEANS separates the function signature (name and parameters) from its implementation (the expression that computes the result).

## Examples

**Example file:** 

```l4-file
-- MEANS keyword examples

-- Basic MEANS Usage

-- Simple value definition
greeting MEANS "Hello, World!"
answer MEANS 42

#EVAL greeting
#EVAL answer

-- Functions with MEANS

GIVEN x IS A NUMBER
double x MEANS x TIMES 2

GIVEN a IS A NUMBER, b IS A NUMBER
add a b MEANS a PLUS b

#EVAL double 21
#EVAL add 10 32

-- Multi-line Function Bodies

GIVEN n IS A NUMBER
GIVETH A NUMBER
factorial n MEANS
  IF n EQUALS 0
  THEN 1
  ELSE n TIMES factorial (n MINUS 1)

#EVAL factorial 6

-- MEANS with WHERE Clauses

GIVEN radius IS A NUMBER
circumference radius MEANS
  2 TIMES pi TIMES radius
  WHERE
    pi MEANS 3.14159

#EVAL circumference 10

-- Nested WHERE
outerFunction MEANS
  innerResult TIMES 2
  WHERE
    innerResult MEANS
      baseValue PLUS 10
      WHERE
        baseValue MEANS 5

#EVAL outerFunction

-- MEANS vs IS Comparison

-- Using MEANS for definitions
valueWithMeans MEANS 100
valueWithMeans2 MEANS 200

#EVAL valueWithMeans
#EVAL valueWithMeans2

-- MEANS in Complex Expressions

GIVEN items IS A LIST OF NUMBER
sumItems items MEANS
  CONSIDER items
  WHEN EMPTY THEN 0
  WHEN head FOLLOWED BY tail THEN head PLUS sumItems tail

#EVAL sumItems (LIST 1, 2, 3, 4, 5)
```



### Basic Usage

```l4
greeting MEANS "Hello, World!"

GIVEN x IS A NUMBER
double x MEANS x TIMES 2
```

### With DECIDE

```l4
DECIDE answer MEANS 42

GIVEN n IS A NUMBER
DECIDE square n MEANS n TIMES n
```

### Multi-line Bodies

```l4
GIVEN n IS A NUMBER
factorial n MEANS
  IF n EQUALS 0
  THEN 1
  ELSE n TIMES factorial (n MINUS 1)
```

### With WHERE Clauses

```l4
circumference radius MEANS
  2 TIMES pi TIMES radius
  WHERE
    pi MEANS 3.14159
```

### In Record Fields (Computed Fields / Methods)

MEANS can also appear inside DECLARE HAS to define computed fields — derived attributes that are calculated automatically from other fields in the record:

```l4
DECLARE Person HAS
    `birth year` IS A NUMBER
    `as at year` IS A NUMBER
    `age`        IS A NUMBER
        MEANS `as at year` - `birth year`
    `adult`      IS A BOOLEAN
        MEANS `age` >= 18
```

The computed field's MEANS body can reference any sibling field by name. It can also call external functions (using OF for multi-argument calls), and use WHERE or LET/IN for local bindings.

See **[DECLARE - Computed Fields](/l4/reference/types/DECLARE.md#computed-fields-methods)** for full documentation.

## Alternative Forms

### Using IS

For simple definitions, IS can replace MEANS:

```l4
answer IS 42
DECIDE pi IS 3.14159
```

### Using BE or MEAN

Alternative keywords (for isomorphism with legal text):

```l4
-- In LET expressions
LET x BE 5 IN x TIMES 2
LET y MEAN 10 IN y PLUS 1
```

## Related Keywords

- **[DECIDE](/l4/reference/functions/DECIDE.md)** - Declares a decision
- **[WHERE](/l4/reference/functions/WHERE.md)** - Local definitions

## Tutorials

- **[Using Infix, Postfix, and Mixfix Functions](/l4/tutorials/natural-language-functions/natural-language-functions.md)** - Define functions that read like natural language