String Interpolation

Fill-in-the-Blanks

Imagine a birthday card template: "Happy Birthday, ____! You are ____ years old." You fill in the blanks with the right name and age.

String interpolation is Pebble's version of fill-in-the-blanks. Instead of joining pieces together with +, you put expressions right inside the string using curly braces {…} and Pebble fills them in for you.

How It Works

Wrap any expression in { and } inside a double-quoted string:

let name = "Alice"
print("hello {name}")   # prints: hello Alice

Pebble evaluates the expression, converts the result to text, and slots it into the string at that position.

Multiple Values

You can have as many {…} sections as you like in one string:

let a = 3
let b = 4
print("{a} + {b} = {a + b}")   # prints: 3 + 4 = 7

Any Expression Works

The bit inside the braces can be any Pebble expression — a variable, a number, a calculation, even a function call:

fn double(n) { return n * 2 }
print("double of 5 is {double(5)}")   # prints: double of 5 is 10

Values are automatically turned into text:

Type	Example	Text
Integer	{42}	42
Float	{3.14}	3.14
String	{"hi"}	hi
Boolean	{true}	true

Literal Braces

If you actually want a { character in your string (not interpolation), put a backslash before it:

print("use \{braces}")   # prints: use {braces}

The \{ is one of several escape sequences Pebble supports. See the escape sequences section in the strings docs for the full list — including \n (newline), \t (tab), \\ (literal backslash), and more.

How It Works Under the Hood

When the lexer sees { inside a string, it splits the string into segments:

"hello {name} end"

becomes the token sequence:

STRING_START("hello ")   →   IDENTIFIER(name)   →   STRING_END(" end")

The parser collects these into a StringInterpolation node. The compiler emits code to push each part onto the stack, then a BUILD_STRING instruction that pops them all and joins them into one string.

Think of it like making a sandwich: each ingredient is stacked up, then BUILD_STRING squashes them all together into one finished sandwich.