# Transpiler from J to Fortran

**URL:** <https://fortran-lang.discourse.group/t/transpiler-from-j-to-fortran/11049>\
**Category:** Uncategorized\
**Created:** [August 15, 2026, 4:09pm UTC](https://fortran-lang.discourse.group/t/transpiler-from-j-to-fortran/11049 "2026-08-15T16:09:52Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Beliavsky](https://avatars.discourse-cdn.com/v4/letter/b/ba8739/32.png) [@Beliavsky](https://fortran-lang.discourse.group/u/Beliavsky)\
**Post date:** [August 15, 2026, 4:09pm UTC](https://fortran-lang.discourse.group/t/transpiler-from-j-to-fortran/11049/1 "2026-08-15T16:09:52Z")

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[J](https://www.jsoftware.com/#/) is an offshoot of APL, co-authored by Iverson, that uses the ASCII character set. Since modern Fortran is also an array programming language, and since it [has been argued](https://martinalderson.com/posts/which-programming-languages-are-most-token-efficient/) that token-efficient languages such as J are a good fit for LLMs, I wrote a transpiler from J to Fortran using OpenAI Sol primarily

> **[GitHub - Beliavsky/J-to-Fortran: Transpiler of a subset of the J programming...](https://github.com/beliavsky/j-to-fortran)**
>
> Transpiler of a subset of the J programming language to modern Fortran

Besides a batch translator there is a REPL that translates and runs Fortran code on the fly. It works on some small J programs, but it cannot handle the more dynamic programs at [GitHub - jonghough/jlearn: Machine Learning Library, written in J · GitHub](https://github.com/jonghough/jlearn) or the programs for astronomy [here](https://pages.astro.umd.edu/~jpha/J_page.html). Claude Opus says that a larger subset of J code could be transpiled to Python/Numpy calling Fortran as needed.

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**Author:** ![jorgeg](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/jorgeg/32/6835_2.png) [@jorgeg](https://fortran-lang.discourse.group/u/jorgeg)\
**Post date:** [August 16, 2026, 6:26am UTC](https://fortran-lang.discourse.group/t/transpiler-from-j-to-fortran/11049/2 "2026-08-16T06:26:46Z")

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I’ve learned about the existence of many programming languages thanks to your transpilers.