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| --- | |
| title: "Functional programming in other languages" | |
| output: rmarkdown::html_vignette | |
| vignette: > | |
| %\VignetteIndexEntry{Functional programming in other languages} | |
| %\VignetteEngine{knitr::rmarkdown} | |
| %\VignetteEncoding{UTF-8} | |
| --- | |
| purrr draws inspiration from many related tools: | |
| * List operations defined in the Haskell [prelude][haskell] | |
| * Scala's [list methods][scala]. | |
| * Functional programming libraries for javascript: | |
| [underscore.js](http://underscorejs.org), | |
| [lodash](https://lodash.com) and | |
| [lazy.js](http://danieltao.com/lazy.js/). | |
| * [rlist](http://renkun.me/rlist/), another R package to support working | |
| with lists. Similar goals but somewhat different philosophy. | |
| However, the goal of purrr is not to try and simulate a purer functional programming language in R; we don't want to implement a second-class version of Haskell in R. The goal is to give you similar expressiveness to an FP language, while allowing you to write code that looks and works like R: | |
| * Instead of point free (tacit) style, we use the pipe, `%>%`, to write code | |
| that can be read from left to right. | |
| * Instead of currying, we use `...` to pass in extra arguments. | |
| * Anonymous functions are verbose in R, so we provide two convenient shorthands. | |
| For unary functions, `~ .x + 1` is equivalent to `function(.x) .x + 1`. | |
| For chains of transformations functions, `. %>% f() %>% g()` is | |
| equivalent to `function(.) . %>% f() %>% g()` (this shortcut is provided | |
| by magrittr). | |
| * R is weakly typed, so we need `map` variants that describe the output type | |
| (like `map_int()`, `map_dbl()`, etc) because we don't know the return type of `.f`. | |
| * R has named arguments, so instead of providing different functions for | |
| minor variations (e.g. `detect()` and `detectLast()`) we use a named | |
| argument, `.right`. Type-stable functions are easy to reason about so | |
| additional arguments will never change the type of the output. | |
| [scala]:http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.List | |
| [haskell]:http://hackage.haskell.org/package/base-4.7.0.1/docs/Prelude.html#g:11 |