# j901 — Explore the J Language > J programming language IDE for data analysis and learning. (iPhone/iPad app by Ian Clark.) - Source: https://appshunter.io/ios/app/j901/id1483497239 (this page in markdown: same URL + `.md`) - Developer: [Ian Clark](https://appshunter.io/developer/1483497238) - Category: Education, Productivity - Price: Free - Rating: 5.00/5 from 8 App Store ratings · 6 written reviews indexed - Age rating: 4+ - Requires: iOS 16.2 · 48 MB - Languages: English - Released: 2021-10-18 - Data updated: 2026-06-10 - Monetization: free - User reviews in markdown: https://appshunter.io/ios/app/j901/id1483497239/reviews.md ## What is j901? J is a general purpose programming language inspired by APL, both languages springing from the fertile mind of the late Ken Iverson. J is particularly strong in the mathematical, statistical, and logical analysis of textual and numerical data. j901 is the follow-on product of j701. This version of the J Integrated Development Environment (J IDE) employs version 9.3 of the J Engine. How J901 differs from J701: * Abandons special keyboard for custom keys on system keyboard * Session log display, whole or part, e.g. inputs-only; or transactions containing a given J primitive or substring * Code editor, with tabs and find facility * Shell-type preprocessor for common housekeeping actions upon jscripts and other files * Separate scenes for displaying the output from "plot" and "viewmat" * Context-sensitive Help; NuVoc lookup * New "Mill" feature for studying noun transformations, e.g. numeric arrays and animated character-graphics such as Conway's Game Of Life Like all J IDEs, this iOS app is offered free of charge as a learning resource for teachers and students of mathematics, statistics, science and engineering. It is also offered without guarantee as a convenience to J experts who normally use a desktop computer for their professional work. Fine-tuned to the iPad, but usable on iPhone, it is first and foremost a vehicle for fun and discovery. DO NOT USE FOR MISSION-CRITICAL WORK – iOS end-user security trumps app recovery. ## Key features - Code editor with tabs and find - Session log display - Context-sensitive help - Mill feature for studying noun transformations - Separate scenes for plot and viewmat output - Shell-type preprocessor ## Recent user reviews (6 of 6) All indexed reviews: https://appshunter.io/ios/app/j901/id1483497239/reviews.md ### 5/5 — Latest update made it stop opening on my iphone XR *2023-04-21* Other than that it's fantastic ### 5/5 — Excellent *2022-12-11, version 1.1* Outstanding port of J to IOS. Very handy. ### 5/5 — J Everywhere *2022-11-14* To paraphrase a well known photographers’ saying, “the best computer language is the one you have with you”. Such a useful tool to have available whenever you need it. Two issues to feedback: 1. the plot package is reported as corrupted. 2. The controls at the top of the screen are partially obscured by the display island/notch on newer iPhones, so are hard to use. As an update, deleting the previous version and then reinstalling from scratch fixed the plot package issue. ### 5/5 — Phenomenal! *2022-10-31, version 1.0* So thankful this was put together! Only programming language I use on my phone ### 5/5 — Great upgrade *2022-07-23* Been using your app 3 weeks, on iPhone, a way better version than J701. Wish there was an APL app too, for iOS, as I find the symbols easier for visualisation / recall, even if I then write it in J! ### 5/5 — Excellent implementation of J. *2021-11-18* Very handy companion to desktop/laptop implementation. Vastly superior to previous implementation. Enjoy J on your phone. ## Frequently asked questions about j901 ### What is j901? j901 is an Integrated Development Environment (IDE) for the J programming language, designed for mathematical, statistical, and logical data analysis. It is a follow-on product to j701, offering enhanced features like a code editor and session logging. ### Is j901 free to use? Yes, j901 is offered free of charge as a learning resource for teachers and students. It is also available to J experts as a convenience. ### What devices does j901 support? j901 is fine-tuned for the iPad but is also usable on the iPhone. It is available on iOS devices. ### How often is j901 updated? The latest version of j901 is 1.2, last updated on April 20, 2023. This indicates a relatively active development cycle for the application. ### What are the key differences between j901 and j701? j901 abandons the special keyboard for custom keys on the system keyboard, includes a session log display, a code editor with tabs, and a new 'Mill' feature for studying noun transformations, among other improvements. ### Can j901 be used for mission-critical work? No, j901 explicitly states it should NOT be used for mission-critical work. iOS end-user security is prioritized over app recovery, making it unsuitable for essential tasks. ### What is the age rating for j901? j901 has an age rating of 4+. This suggests it is suitable for a wide range of users, including younger learners interested in programming. ### Does j901 have ads? No, j901 does not contain advertisements. It is offered as a free learning resource without any ad interruptions. ## Version history (last 3 releases) ### 1.2 — 2023-04-20 Unbundling factory files and folders is now under end-user control: app updates now leave the sandbox (j/ folder) unaltered. Watched nouns replace 2!:9 (ui) for all except system use. Watched noun: noun: CLIP_i_ replaces verbs: getclip and: setclip for accessing the system pasteboard. Hotkey ⌘E now toggles between Home and Edit. Troublesome verb: monadspaced eliminated, so that syntax coloring no longer relies on system J code residing in the sandbox. Choose 4 styles of syntax coloring (0:eclectic, 1:jqt, 2:nuvoc, 3:nuvoc nearest system color) via a watched noun: SYNTAX_COLOR_SCHEME_i_. Edit: trailing blank lines are now tolerated; CRLF in imported scripts is now coverted to LF; the J sentence "if. 1 do." is now correctly colored. ### 1.1 — 2022-11-11 * on-screen keyboard extra keys: [_z_] [`] [''] * optional syntax coloring and line numbering in the jscript editor * option to balance parentheses and quotes in an input sentence * new factory j-words, e.g. display, editwd * three recommended fontsizes for J code: small, medium, large * new spx tutorials for J learning and reference * watched nouns to augment or replace 2!:9 control of the app's UI * improved app UI menus * standard "JAL" addons library augmented and updated to latest versions ### 1.0 — 2021-10-18 No release notes. ## Apps similar to j901 | App | Rating | Price | Category | | --- | --- | --- | --- | | [PiBase: Topology](https://appshunter.io/ios/app/pibase-topology/id1612405297) | 5.0 (1) | Free | Education | | [cl-repl](https://appshunter.io/ios/app/cl-repl/id1511296102) | 4.9 (21) | Free | Education | | [Shen Programming Language](https://appshunter.io/ios/app/shen-programming-language/id1256936517) | 5.0 (1) | $1.99 | Education | | [Stochastic Signal Processing](https://appshunter.io/ios/app/stochastic-signal-processing/id1450268179) | 4.6 (5) | Free | Education | | [Промышленная безопасность 2025](https://appshunter.io/ios/app/2025/id1619674480) | 4.9 (38) | Free | Education | | [The Bounty Collegium](https://appshunter.io/ios/app/the-bounty-collegium/id1661433420) | 5.0 (6) | Free | Education | --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-06-10.*