---
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)
```