---
CommandName: throw
ManualSection: n
Version: 8.6
TclPart: Tcl
TclDescription: Tcl Built-In Commands
Links:
 - catch(n)
 - error(n)
 - errorCode(n)
 - errorInfo(n)
 - return(n)
 - try(n)
Keywords:
 - error
 - exception
Copyright:
 - Copyright (c) 2008 Donal K. Fellows
---

# Name

throw - Generate a machine-readable error

# Synopsis

::: {.synopsis} :::
[throw]{.cmd} [type]{.arg} [message]{.arg}
:::

# Description

This command causes the current evaluation to be unwound with an error. The error created is described by the *type* and *message* arguments: *type* must contain a list of words describing the error in a form that is machine-readable (and which will form the error-code part of the result dictionary), and *message* should contain text that is intended for display to a human being.

The stack will be unwound until the error is trapped by a suitable **catch** or **try** command. If it reaches the event loop without being trapped, it will be reported through the **bgerror** mechanism. If it reaches the top level of script evaluation in **tclsh**, it will be printed on the console before, in the non-interactive case, causing an exit (the behavior in other programs will depend on the details of how Tcl is embedded and used).

By convention, the words in the *type* argument should go from most general to most specific.

# Examples

The following produces an error that is identical to that produced by **expr** when trying to divide a value by zero.

```
throw {ARITH DIVZERO {divide by zero}} {divide by zero}
```