Bang Notation

!<function>(<args>)
!!<function>(<args>)
!$<function>(<args>), !!$<function>(<args>)
!^<function>(<args>), !!^<function>(<args>)

A function call with one or two ! before its name gives 1 or 0 about its result instead of the result. One ! gives 1 when the test fails, two give 1 when it passes:

! and !! test the number the result starts with: ! is 1 when it is 0 or there is none, !! when it is not 0.
!$ and !!$ test for text: !$ is 1 when the result is empty, !!$ when it is not.
!^ and !!^ test truth the way t() does: !^ is like not(), !!^ like t().

The idea comes from RhostMUSH. PennMUSH has no bangs: there !strlen(abc) is text, and [!strlen(abc)] is an unknown function.

bang notation placement: where a bang is read, and bangs in substitutions
bang notation examples: bangs on functions and registers

::: seealso

Where a bang works

A bang works only where a function call is recognised: at the start of an argument or a command’s text, or right after [. It works on any function, @functions included. Anywhere else, and before a name that is not a function, the ! is plain text, so !wow, x!strlen(abc) and ![strlen(abc)] stay as they are.

The same bangs work before the name in %q<name>, and before the number in %i<n>, %i_<n>, %-<n> and %d<n> (or the L of %iL and %i_L): %q<!!$name> is 1 when the register is set to something, %i!0 is 1 when the iteration’s element is 0, %-!!$1 is 1 when there is a second argument.

Bang examples

> think [!strlen(abc)] [!!strlen(abc)] [!strlen()]
0 1 1

> think add(!!strlen(abc),5)
6

> think [setq(name,)][if(%q<!$name>,No name.,Hello %q<name>.)]
No name.

> think iter(0 1 2,%i!!0)
0 1 1

> think ![strlen(abc)] x!strlen(abc)
!3 x!strlen(abc)