Programming Flix

String Interpolation

Flix strings support interpolation. Inside a string, the form "${e}" evaluates e to a value and converts it to a string using the ToString trait. For example:

let fstName = "Lucky";
let lstName = "Luke";
"Hello Mr. ${lstName}. Do you feel ${fstName}, punk?"

String interpolation works for any type that implements a ToString instance. For example:

let i = 123;
let o = Some(123);
let l = 1 :: 2 :: 3 :: Nil;
"i = ${i}, o = ${o}, l = ${l}"

String interpolations may contain arbitrary expressions. For example:

let x = 1;
let y = 2;
"${x + y + 1}"

String interpolation is the preferred way to concatenate two strings:

let x = "Hello";
let y = "World";
"${x}${y}" // equivalent to x + y

String interpolation is the preferred way to convert a value to a string:

let o = Some(123);
"${o}"

which is equivalent to an explicit use of the toString function from the ToString trait:

ToString.toString(o)

String interpolators may nest, but this is discouraged.