rcl/docs/strings.md

Strings

RCL has multiple forms of string literals. String literals in RCL support string interpolation and are most similar to those in Python, with some inspiration from Nix and Rust. All json strings are valid in RCL¹.

Strings can be quoted with double quotes:

"Hello, world"

Or with triple double quotes:

"""
Hello, world
"""

In both cases, add an f to enable interpolation.

f"Hello {greetee}"

Multiline strings

In all string literals, newlines are preserved verbatim. Inside a """-quoted string, any shared leading whitespace gets removed, as well as the mandatory newline that directly follows the """. If there is a trailing newline, then that one is part of the string. The following strings are identical:

let a = "Hello\n  World\n";
let b = "Hello
  World\n";
let c =
  """
  Hello
    World
  """;
let d =
  """
    Hello
      World\n""";

Inside a "-quoted string, " itself needs to be escaped as \", but inside a """-quoted string, " does not need to be escaped. Inside a """-quoted string, """ itself needs to be escaped, but escaping one of the three quotes is sufficient.

Blank lines inside the string do not defeat shared leading whitespace. This means that the following expression returns true without any of the lines in the document containing trailing whitespace:

let x =
   """
   Section 1

   Section 2
   """;
let y = "Section 1\n\nSection 2\n";
x == y

Interpolation

When an f precedes a string literal, this enables interpolation, and the string is called a format string or f-string for short. Interpolation means that the string literal should have one or more holes, delimited by {}. The hole can contain any expression that evaluates to a string. (TODO: How to type string formattable types?). Holes can themselves contain format strings, there is no nesting limitation. (Like in Nix, but unlike Python.)

An example of string interpolation:

let generations = {
  "Leon Kowalski": 6,
  "Rachael": 7,
  "Roy Batty": 6,
};
[
  for name, generation in generations:
  f"{name} was a Nexus-{generation} replicant."
]

Escape sequences

Inside strings, \ initiates an escape sequence. The same escape sequences as in json are supported, which includes \", \\, \r, \n, and \t. Furthermore, \{ escapes { inside format strings. } does not need to be escaped, but for symmetry \} is allowed as an escape for }.

A \u initiates an escape sequence for an arbitrary Unicode scalar value. It can be followed by either exactly 4 hex digits (like in json and Python), or by a variable number of hex digits enclosed in {} (like in Rust). The following strings are identical:

let a = "\n";
let b = "\u000a";
let c = "\u{0a}";
let d = "\u{00000a}";

---

1. Except for \u escape sequences that encode surrogate code points (U+D800 through U+DFFF). While a pair of such escape sequences may together be valid, a single one is not, so at this point RCL opts to not implement surrogate pairs. ↩︎