Strings and interpolation

A string is a run of text. There are two ways to write one, and the difference is whether it interpolates.

The two forms

Double quotes "..." interpolate. Inside them, $name is replaced by a variable's value and [cmd …] is replaced by a command's result.
Single quotes '...' are literal. What you type is exactly the string — no $ or [ substitution happens.

do "say hello [name $actor]"     # interpolates: "say hello Puff"
do 'say hello [name $actor]'     # literal: the text [name $actor] is sent

Use single quotes for fixed text and for anything containing $ or [ that should stay literal; use double quotes when you want to splice values in.

Interpolation

Inside a "..." string, two substitutions are recognized:

$name or ${name} — replaced by the variable's value, converted to text. In the bare $name form the name runs only while characters are letters, digits, or _, so "$x-1" reads x then appends the literal -1. The braced ${name} form ends at the }, which is how you glue a name to following letters: "${count}coins".
[cmd …] — the command is run and its result spliced in.

do "say [name $actor] is level [level $actor]"

Against a level-26 actor named Puff this sends "Puff is level 26." Any value converts to text for this purpose (see Values — conversion to text); that is the language's one automatic conversion.

To put a literal $ or [ into a double-quoted string, escape it: \$ and \[. Both quote forms also accept \n (line feed), \t (tab), and \\ (backslash); a double-quoted string additionally takes \", and a single-quoted one \'.

Building text — interpolate, don't concatenate

There is no concat command. To build a string from pieces, write a double-quoted string and interpolate the pieces:

after command (say) {
  let mood 'cheerful'
  do "say I am feeling $mood today, [name $actor]."
}

This is the idiomatic way to assemble any dynamic message — for echo, do, emote, and so on.

Strings are not iterable

A string is a single value. To walk its words, convert it with words:

each [words "north east south west"] { <dir>
  do "say I could go $dir."
}

See Iterables for why a bare string can't be iterated directly.

Comparing strings