stan-dev/stanc3

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The Stan transpiler (from Stan to C++ and beyond).

Stars: 160
Forks: 59
Open beginner issues: 0
Indexed issues: 83
Avg merge: 21h 45m
Merged PRs (30d): 26

Dominant language: OCaml
License: BSD-3-Clause
Last GitHub push: Sep 17, 2026
Latest indexed: Sep 19, 2026
Contributing guide: No contributing guide
Code of conduct: No code of conduct
Beginner labels: help wanted good first issue

Beginner friendly Everything

Open All

83 open issues indexed

Stan math should have specific type traits only the compiler uses Open

cpp-codegen feature performance

Difficulty 5/5 Over a week Newbie friendliness 35/100

stan-dev/stanc3#1722 · 5 comments · Opened Sep 16, 2026
Add `std::move` optimization to last use of matrix and array like objects Open

feature optimization

Difficulty 5/5 Over a week Newbie friendliness 30/100

stan-dev/stanc3#1721 · Opened Sep 16, 2026
Two more loop shapes for vectorize_loops Open

optimization

Difficulty 5/5 Over a week Newbie friendliness 45/100

stan-dev/stanc3#1705 · 1 comment · 1 reaction · Opened Sep 10, 2026
pairwise indexing arrays of varying effects Open

feature

Difficulty 5/5 Over a week Newbie friendliness 35/100

stan-dev/stanc3#1704 · 1 comment · Opened Sep 10, 2026
Recognize regressions as GLMs Open

feature optimization

Difficulty 5/5 Over a week Newbie friendliness 35/100

stan-dev/stanc3#1697 · 2 comments · Opened Sep 6, 2026
Post-2.40: Move loop vectorization to O1 Open

optimization

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#1692 · Opened Sep 3, 2026
Expose map functions Open

feature typechecker

Difficulty 4/5 3-5 days Newbie friendliness 45/100

stan-dev/stanc3#1680 · Opened Aug 26, 2026
Peephole optimization for commonly paired functions Open

feature help wanted optimization performance

Difficulty 4/5 3-5 days Newbie friendliness 42/100

stan-dev/stanc3#1677 · Opened Aug 24, 2026
Function `gradient` for nested autodiff of user defined functions Open

feature

Difficulty 5/5 Over a week Newbie friendliness 35/100

stan-dev/stanc3#1675 · 2 comments · Opened Aug 24, 2026
FR: Allow UDFs to vary only in `data` annotations Open

typechecker

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#1531 · 6 comments · Opened Jul 23, 2025
Flag to disallow functions without higher order derivatives Open

feature good first issue help wanted typechecker

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stanc3#1529 · 2 comments · Opened Jul 1, 2025
hook to write transformed data as JSON string Open

feature

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#1522 · 7 comments · Opened Jun 16, 2025
SoA should allow arbitrary initialization of matrix if it isn't elementwise accessed thereafter Open

optimization

Difficulty 5/5 Over a week Newbie friendliness 35/100

stan-dev/stanc3#1503 · Opened Mar 13, 2025
Typechecker: Allow easier modification of standard library Open

cleanup typechecker

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#1500 · Opened Mar 10, 2025
Allowing `_lp` in the transformed parameters block and `jacobian` in the model block Open

feature

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#1482 · 8 comments · Opened Dec 18, 2024
Kronecker Products Open

feature

Difficulty 5/5 Over a week Newbie friendliness 20/100

stan-dev/stanc3#1454 · 9 comments · Opened Oct 10, 2024
Explore variadic map_rect Open

feature

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#1448 · 1 comment · Opened Sep 23, 2024
[FR] Add `lower_upper` constrain Open

feature good first issue

Difficulty 5/5 Over a week Newbie friendliness 38/100

stan-dev/stanc3#1438 · 5 comments · Opened Jul 15, 2024
[BUG] SoA request is ignored with external c++ Open

cpp-codegen optimization

Difficulty 3/5 1-2 days Newbie friendliness 35/100

stan-dev/stanc3#1379 · 5 comments · Opened Nov 30, 2023
Typechecker: Allow predicate-based typechecking of library functions Open

Difficulty 5/5 Over a week Newbie friendliness 30/100

stan-dev/stanc3#1373 · 3 comments · Opened Nov 3, 2023
[FR] Bool data type? Open

feature

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#1328 · 1 comment · Opened May 11, 2023
[FR] UDFs taking another UDF as argument Open

feature

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#1325 · 1 comment · Opened May 8, 2023
[BUG] Compiler optimizations can prevent bounds checks Open

bug cpp-codegen optimization robustness

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stanc3#1295 · 3 comments · Opened Mar 20, 2023
SoA optimization can over-promote objects used inside loops to produce slower code Open

bug cpp-codegen optimization

Difficulty 4/5 3-5 days Newbie friendliness 25/100

stan-dev/stanc3#1280 · Opened Jan 23, 2023
Improving external C++ integration Open

cpp-codegen feature interface

stan-dev/stanc3#1278 · 4 comments · 1 assignee · Opened Jan 12, 2023
[FR] Allow SoA for UDFs Open

feature optimization

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#1237 · 1 comment · Opened Aug 8, 2022
[FR] `reduce_sum` does not block `SoA` Open

feature optimization

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stanc3#1236 · 3 comments · Opened Aug 8, 2022
Investigate function inlining in transformed data block Open

bug optimization

Difficulty 4/5 3-5 days Newbie friendliness 30/100

stan-dev/stanc3#1219 · Opened Jun 23, 2022
Developer doc: describe debug process Open

documentation

Difficulty 3/5 1-2 days Newbie friendliness 48/100

stan-dev/stanc3#1134 · 4 comments · Opened Feb 24, 2022
Partial evaluator should not silently swallow errors Open

cleanup good first issue optimization

Difficulty 4/5 3-5 days Newbie friendliness 42/100

stan-dev/stanc3#1125 · Opened Feb 18, 2022
Delegate ternary operator to Math `if_else()` Open

feature

Difficulty 4/5 3-5 days Newbie friendliness 42/100

stan-dev/stanc3#1086 · 5 comments · Opened Jan 3, 2022
FR: Matrix inputs to multi_normal_* Open

feature

Difficulty 5/5 Over a week Newbie friendliness 30/100

stan-dev/stanc3#937 · 2 comments · Opened Jul 27, 2021
Pedantic-mode missing prior false alarm Open

Difficulty 4/5 3-5 days Newbie friendliness 30/100

stan-dev/stanc3#932 · 2 comments · Opened Jul 23, 2021
FR: dimension links to inputs with `--info` Open

feature

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stanc3#904 · 2 comments · Opened May 19, 2021
Optimize code by merging expressions Open

optimization

Difficulty 5/5 Over a week Newbie friendliness 35/100

stan-dev/stanc3#860 · 1 comment · 2 reactions · Opened Mar 23, 2021
reduce_log_sum_exp function, aka reduce_sum for mixtures Open

feature

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#841 · 23 comments · 5 reactions · Opened Mar 6, 2021
Chained comparison Open

feature good first issue

Difficulty 5/5 Over a week Newbie friendliness 35/100

stan-dev/stanc3#823 · 1 reaction · Opened Feb 22, 2021
[Q] A few questions on additional variable metadata and C++ codegen Open

question

Difficulty 5/5 Over a week Newbie friendliness 20/100

stan-dev/stanc3#812 · 21 comments · Opened Feb 11, 2021
Add vectorised signatures for categorical, categorical_logit, and ordered_logistic Open

feature

stan-dev/stanc3#782 · 1 comment · 1 assignee · Opened Dec 30, 2020
[FR] Convert indices to more efficient versions Open

feature optimization

Difficulty 4/5 3-5 days Newbie friendliness 45/100

stan-dev/stanc3#769 · Opened Dec 16, 2020
pedantic mode incorrectly warning about 2 priors? Open

bug

Difficulty 3/5 1-2 days Newbie friendliness 42/100

stan-dev/stanc3#746 · 5 comments · Opened Nov 19, 2020
Future Request: Using arena_t in the model class Open

feature performance

Difficulty 5/5 Over a week Newbie friendliness 15/100

stan-dev/stanc3#736 · 21 comments · 2 reactions · Opened Oct 28, 2020
Can't mix offset/multiplier with upper/lower bounds Open

feature

Difficulty 4/5 3-5 days Newbie friendliness 25/100

stan-dev/stanc3#659 · 24 comments · Opened Jul 31, 2020
Simplify parser Open

cleanup parsing

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#614 · 1 comment · Opened Jul 7, 2020
Optimization efficacy and efficiency Open

optimization

Difficulty 5/5 Over a week Newbie friendliness 20/100

stan-dev/stanc3#555 · 2 comments · Opened May 29, 2020
Why are declarations and allocations done on different lines in write_array? Open

cpp-codegen optimization

Difficulty 4/5 3-5 days Newbie friendliness 25/100

stan-dev/stanc3#503 · 9 comments · Opened Apr 9, 2020
Need help with sparse matrix for loop code Open

optimization

Difficulty 4/5 3-5 days Newbie friendliness 25/100

stan-dev/stanc3#488 · 1 comment · Opened Mar 24, 2020
restrict map_rect to legal data-only args Open

bug feature

Difficulty 4/5 3-5 days Newbie friendliness 42/100

stan-dev/stanc3#441 · 7 comments · Opened Jan 23, 2020
Don't print cuts between empty blocks in pretty printer Open

cleanup cpp-codegen good first issue

Difficulty 2/5 1-3 hours Newbie friendliness 25/100

stan-dev/stanc3#354 · Opened Oct 23, 2019
See if we can do map_rect data transfers in stanc3 and get rid of call_id template parameter Open

cleanup cpp-codegen

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stanc3#332 · 2 comments · Opened Oct 11, 2019

stan-dev/stanc3

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