Add converting codepoints to characters

core/src/ast.rs

@@ -544,6 +544,20 @@ fn evaluate_as<I: Interrupt>(
 				}
 				return Err(FendError::ExpectedAString);
 			}
+			"char" | "character" => {
+				let a = evaluate(a, scope, attrs, context, int)?;
+				if let Value::Num(v) = a {
+					let n = v.try_as_usize(int)?;
+					let ch = n
+						.try_into()
+						.ok()
+						.and_then(std::char::from_u32)
+						.ok_or(FendError::InvalidCodepoint(n))?;
+
+					return Ok(Value::String(ch.to_string().into()));
+				}
+				return Err(FendError::ExpectedANumber);
+			}
 			_ => (),
 		}
 	}

core/src/error.rs

@@ -51,6 +51,7 @@ pub(crate) enum FendError {
 	ExpectedACharacter,
 	StringCannotBeLonger,
 	StringCannotBeEmpty,
+	InvalidCodepoint(usize),
 	ExpectedADigit(char),
 	ExpectedChar(char, char),
 	ExpectedDigitSeparator(char),
@@ -160,6 +161,9 @@ impl fmt::Display for FendError {
 			Self::ExpectedARealNumber => write!(f, "expected a real number"),
 			Self::StringCannotBeLonger => write!(f, "string cannot be longer than one codepoint"),
 			Self::StringCannotBeEmpty => write!(f, "string cannot be empty"),
+			Self::InvalidCodepoint(codepoint) => {
+				write!(f, "invalid codepoint: U+{codepoint:04x}")
+			}
 			Self::UnableToGetCurrentDate => write!(f, "unable to get the current date"),
 			Self::NegativeNumbersNotAllowed => write!(f, "negative numbers are not allowed"),
 			Self::ProbabilityDistributionsNotAllowed => {