---

title: "lambda Function Builder"

author: "John Mount"

date: "`r Sys.Date()`"

output: rmarkdown::html_vignette

vignette: >

%\VignetteIndexEntry{lambda Function Builder}

%\VignetteEngine{knitr::rmarkdown}

%\VignetteEncoding{UTF-8}

---

The [`CRAN`](https://cran.r-project.org) version of the [`R`](https://www.r-project.org) package [`wrapr`](https://CRAN.R-project.org/package=wrapr) package now includes a concise anonymous function constructor: `l()`.

To use it please do the following: attach `wrapr` and ask it to place a definition for `l()` in your environment:

```{r wrapri}

library("wrapr")

wrapr::defineLambda(name = "l")

ls()

```

Note: throughout this document we are using the letter "`l`" as a stand-in for the Greek letter lambda, as this non-ASCII character can cause formatting problems in some situations.

You can use `l()` to define functions. The syntax is: `l(arg [, arg]*, body [, env=env])`. That

is we write a `l()`-call (which you can do by cutting and pasting) and list the desired function arguments and then the function body. For example the function that squares numbers is:

```{r fsq1}

l(x, x^2)

```

We can use such a function to square the first four positive integers as follows:

```{r fsq2}

sapply(1:4, l(x, x^2))

```

Dot-pipe style notation does not need the `l()` factory as it treats pipe stages

as expressions parameterized over the variable "`.`":

```{r fsqp}

1:4 %.>% { .^2 }

```

And we can also build functions that take more than one argument as follows:

```{r ft}

l(x, y, x + 3*y)

```