Showing answers

format_value(&value, &options) returns a Formatted: the text to show and an exact flag that is false when the text differs from the true value because of rounding.

FormatOptions

FormatOptions::default() is what the app shows with no settings changed: ten decimal places at most, thousands separators, k and M for large numbers, and the North American number format. Change a copy of it, never the global default.

use babbage_core::{FormatOptions, evaluate, format_value};

let value = evaluate("2/3")?;
let two = FormatOptions::new(2)?;
assert_eq!(format_value(&value, &two).text, "0.67");

let repeating = FormatOptions::default().with_repeating(true);
assert_eq!(format_value(&value, &repeating).text, "0.(6)");

FormatOptions::new refuses more than 1000 decimal places with Error::InvalidPrecision. with_repeating(true) writes a repeating decimal with its period in brackets, up to MAX_REPEAT_PERIOD digits, and falls back to a rounded decimal beyond that.

Number formats

NumberFormat picks the marks for thousands and for the decimal point. It changes how numbers are written, and how they are read in a line.

use babbage_core::{FormatOptions, NumberFormat, evaluate, format_value};

let value = evaluate("1234.5")?;
let europe = FormatOptions::default().in_format(NumberFormat::WesternEurope);
assert_eq!(format_value(&value, &europe).text, "1.234,5");
assert_eq!(format_value(&value, &FormatOptions::default()).text, "1,234.5");

Large numbers and money

Large numbers are abbreviated by default (16.7M). Switch that off for every digit.

use babbage_core::{FormatOptions, evaluate, format_value};

let value = evaluate("256 * 256 * 256")?;
assert_eq!(format_value(&value, &FormatOptions::default()).text, "16.777216M");
let all = FormatOptions::default().unabbreviated();
assert_eq!(format_value(&value, &all).text, "16,777,216");

Money keeps its symbol and its cents: $60.00, not 60. The fields currency_codes (5.00 EUR instead of €5.00) and money_trim_zeros ($5 instead of $5.00) change that.

The options a user has set

A program with its own settings screen usually does not build FormatOptions by hand. Settings::format_options() turns a Settings value (see Settings and time) into the options it implies.