Recipes

A calculator for lines on standard input

Read the lines, evaluate them as one sheet, and print each answer beside its line. This is the whole idea of the bbg command, minus its options.

use babbage_core::{FormatOptions, LineKind, SheetOptions, evaluate_sheet, format_value};

fn answers(text: &str) -> Vec<String> {
    let lines: Vec<&str> = text.lines().collect();
    let results = evaluate_sheet(&lines, &SheetOptions::default());
    let opts = FormatOptions::default();
    lines
        .iter()
        .zip(&results)
        .map(|(line, result)| match &result.kind {
            LineKind::Value(v) => format!("{line}  =  {}", format_value(v, &opts).text),
            LineKind::Error(e) => format!("{line}  !  {e}"),
            _ => (*line).to_string(),
        })
        .collect()
}

let out = answers("rent = $900\nrent * 12\n5 kg in m");
assert_eq!(out[1], "rent * 12  =  $10,800.00");
assert_eq!(out[2], "5 kg in m  !  these units measure different things");

One call that gives text

When all you need is the answer to one line as a string, wrap the two calls once and keep the error:

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

fn calc(line: &str) -> Result<String, Error> {
    Ok(format_value(&evaluate(line)?, &FormatOptions::default()).text)
}

assert_eq!(calc("20% of 85")?, "17");
assert!(calc("20% of").is_err());

Answers inside text

A note-taking program can answer calculations written in running text. Treat a line that ends in = as a question:

use babbage_core::{FormatOptions, LineKind, SheetOptions, evaluate_sheet, format_value};

fn fill_in(line: &str) -> String {
    let Some(question) = line.trim_end().strip_suffix('=') else {
        return line.to_string();
    };
    // A sheet of one line reads the words around the sum the way the app does: "Tip on the bill:" is a label.
    match &evaluate_sheet(&[question], &SheetOptions::default())[0].kind {
        LineKind::Value(v) => format!("{question}= {}", format_value(v, &FormatOptions::default()).text),
        _ => line.to_string(),
    }
}

assert_eq!(fill_in("Tip on the bill: 18% of 64 ="), "Tip on the bill: 18% of 64 = 11.52");
assert_eq!(fill_in("nothing to do here"), "nothing to do here");

Lines that are not a calculation are left alone, which is the safe thing for a text editor to do. A whole note can go to evaluate_sheet in one call, so that names and earlier answers work too; read ignored on each result to see which words were skipped.