Excel LAMBDA() function: Example of using the Excel 365 LAMBDA() function

An example of using the new Excel LAMBDA() function with therust_xlsxwriter library.

See also The Excel 365 LAMBDA() function.

Image of the output file:

Code to generate the output file:

// SPDX-License-Identifier: MIT OR Apache-2.0
//
// Copyright 2022-2025, John McNamara, jmcnamara@cpan.org

//! An example of using the new Excel LAMBDA() function with the `rust_xlsxwriter`
//! library.

use rust_xlsxwriter::{Workbook, XlsxError};

fn main() -> Result<(), XlsxError> {
    // Create a new Excel file object.
    let mut workbook = Workbook::new();

    // Write a Lambda function to convert Fahrenheit to Celsius to a cell as a
    // defined name and use that to calculate a value.
    //
    // Note that the formula name is prefixed with "_xlfn." (this is normally
    // converted automatically by write_formula*() but isn't for defined names)
    // and note that the lambda function parameters are prefixed with "_xlpm.".
    // These prefixes won't show up in Excel.
    workbook.define_name(
        "ToCelsius",
        "=_xlfn.LAMBDA(_xlpm.temp, (5/9) * (_xlpm.temp-32))",
    )?;

    // Add a worksheet to the workbook.
    let worksheet = workbook.add_worksheet();

    // Write the same Lambda function as a cell formula.
    //
    // Note that the lambda function parameters must be prefixed with "_xlpm.".
    // These prefixes won't show up in Excel.
    worksheet.write_formula(0, 0, "=LAMBDA(_xlpm.temp, (5/9) * (_xlpm.temp-32))(32)")?;

    // The user defined name needs to be written explicitly as a dynamic array
    // formula.
    worksheet.write_dynamic_formula(1, 0, "=ToCelsius(212)")?;

    // Save the file to disk.
    workbook.save("lambda.xlsx")?;

    Ok(())
}