# Symbol Goto

# → — Branch to a line in a function — Keystroke ALT+] — Character 8594 or 0x2192

## Alternate Names

This symbol is also known as right arrow or APL text symbol **{rightarrow}**.

## Usage

The goto symbol may be used as a conditional branch (branch based on a comparison) or an unconditional branch, or it may be used to exit a function. It is most often used in a function to transfer control, but can be used from the session manager to transfer to a line in a suspended function.

### Conditional branch

The value to the right of the arrow is a boolean expression or non-negative number surrounded by parentheses, followed by a slash symbol and the line number to transfer to if the expression is true for a boolean expression or nonzero for a numeric value. A DOMAIN ERROR occurs if the numeric value is negative. In the following line 5 of a function:

`[5] →(A<1)/22`

Will branch to line 22 of the function if the value of A is less than 1. Execution would continue on line 6 if A was 1 or more.

As per the example from above, there are syntactically __three parts to a conditional branch__:

- Leftmost, the branch symbol itself,
**→** - Boolean test to perform, usually within parentheses,
**(A<1)** - Statement number or label to go to if the test within parentheses is true(1),
**/22**- note use of the reduction or slash symbol.

The test inside the parentheses may be ** simple**, as per the above example. The branch's boolean test may also be

**, ref. the following:**

__compound__**→((A<1)∨(A>10))/OR_Case**

In this example if **A** is less than 1 OR **A** is greater than 10, the user function will branch to line label **OR_Case:** in the function. This occurs because if __either__ test is true, the compound test evaluates to true - union of 2 tests(boolean 1 in either test results in a branch).

Another compound or dual boolean test, this time a boolean AND:

**→((A<1)∧(A>-10))/AND_NegativeCase**

Branching will occur only if BOTH tests evaluate to true. The user function will go to line label AND_NegativeCase: in the function only if (-10<A<1) or if **A∊(-9 -8 -7 -6 -5 -4 -3 -2 -1 0}** - intersection of 2 tests(boolean 1 if BOTH tests evaluate to true results in a branch).

In setting up boolean **go to** tests also bear in mind use of APL's **∼** or **not** symbol, thus:

`[5] →(∼A<1)/22`

Thus APL would go to line number 22 only if A is greater than or equal to 1.

### Unconditional branch

The goto symbol is followed on the right either by the line number or a label. Execution continues in the function at that line (unless the line specified is 0, in which case the function exits.)

### Exit Function

The goto symbol may be used to exit a function and return to the calling function (or return to the session manager if the function was called by the user typing its name) by using 0 as the line number to goto. This is the same as `:return`

## Examples

### Exit Function

In the following example, function one calls function two, which exits part way through the function, returning to function 1.
`
`

- ∆one

[0] one

[1] 'This is one'

[2] two

[3] 'return to one from two'

- ∆

- ∆two

[0] two

[1] 'This is two'

[2] →0

[3] 'Two Continues'

- ∆

- one

`This is one
This is two
return to one from two
`

### Label Branch

`
`

- ∆three

[0] three arg

[1] →(arg=0)/dbz

[2] '3/',arg,'=',3/arg

[3] →end

[4] dbz: 'Cannot divide by zero'

[5] end:

- ∆

- three 0

Cannot divide by zero

- three 6

`3/ 6= 0.5
`

## See also

Another Example see: **Control Structures - Branching Example**

See also: **Symbol Tilde or Not and Symbol Slash or Reduce**

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