EVOLUTION-MANAGER

Edit File: other-langs.Rmd

--- 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