dafny
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dafny | SharpLab | |
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30 | 104 | |
2,641 | 2,524 | |
1.5% | - | |
9.7 | 7.8 | |
3 days ago | 3 months ago | |
C# | C# | |
GNU General Public License v3.0 or later | BSD 2-clause "Simplified" License |
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dafny
- Candy – a minimalistic functional programming language
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Lean4 helped Terence Tao discover a small bug in his recent paper
Code correctness is a lost art. I requirement to think in abstractions is what scares a lot of devs to avoid it. The higher abstraction language (formal specs) focus on a dedicated language to describe code, whereas lower abstractions (code contracts) basically replace validation logic with a better model.
C# once had Code Contracts[1]; a simple yet powerful way to make formal specifications. The contracts was checked at compile time using the Z3 SMT solver[2]. It was unfortunately deprecated after a few years[3] and once removed from the .NET Runtime it was declared dead.
The closest thing C# now have is probably Dafny[4] while the C# dev guys still try to figure out how to implement it directly in the language[5].
[1] https://www.microsoft.com/en-us/research/project/code-contra...
[2] https://github.com/Z3Prover/z3
[3] https://github.com/microsoft/CodeContracts
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The Deep Link Equating Math Proofs and Computer Programs
I don't think something that specific exists. There are a very large number of formal methods tools, each with different specialties / domains.
For verification with proof assistants, [Software Foundations](https://softwarefoundations.cis.upenn.edu/) and [Concrete Semantics](http://concrete-semantics.org/) are both solid.
For verification via model checking, you can check out [Learn TLA+](https://learntla.com/), and the more theoretical [Specifying Systems](https://lamport.azurewebsites.net/tla/book-02-08-08.pdf).
For more theory, check out [Formal Reasoning About Programs](http://adam.chlipala.net/frap/).
And for general projects look at [F*](https://www.fstar-lang.org/) and [Dafny](https://dafny.org/).
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In Which I Claim Rich Hickey Is Wrong
Dafny and Whiley are two examples with explicit verification support. Idris and other dependently typed languages should all be rich enough to express the required predicate but might not necessarily be able to accept a reasonable implementation as proof. Isabelle, Lean, Coq, and other theorem provers definitely can express the capability but aren't going to churn out much in the way of executable programs; they're more useful to guide an implementation in a more practical functional language but then the proof is separated from the implementation, and you could also use tools like TLA+.
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Programming Languages Going Above and Beyond
> I think we can assume it won't be as efficient has hand written code
Actually, surprisingly, not necessarily the case!
If you'll refer to the discussion in https://github.com/dafny-lang/dafny/issues/601 and in https://github.com/dafny-lang/dafny/issues/547, Dafny can statically prove that certain compiler branches are not possible and will never be taken (such as out-of-bounds on index access, logical assumptions about whether a value is greater than or less than some other value, etc). This lets you code in the assumptions (__assume in C++ or unreachable_unchecked() under rust) that will allow the compiler to optimize the codegen using this information.
The language (Dafny): https://github.com/dafny-lang/dafny
Dafny is a verification-ready programming language. As you type in your program, Dafny's verifier constantly looks over your shoulder, flags any errors, shows you counterexamples, and congratulates you when your code matches your specifications. When you're done, Dafny can compile your code to C#, Go, Python, Java, or JavaScript (more to come!), so it can integrate with your existing workflow.
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What are the current hot topics in type theory and static analysis?
Most of the proof assistants out there: Lean, Coq, Dafny, Isabelle, F*, Idris 2, and Agda. And the main concepts are dependent types, Homotopy Type Theory AKA HoTT, and Category Theory. Warning: HoTT and Category Theory are really dense, you're going to really need to research them.
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What I've Learned About Formal Methods in Half a Year
I'm not sure if the author is here, or if my comment attempt was successful. So, can I suggest you take a look at a third leg of the formal methods stool?
If you are familiar with C, check out Frama-C (https://frama-c.com/) and the WP and RTE plugins. The approach is based on Tony Hoare and EWD's axiomatic semantics (https://en.wikipedia.org/wiki/Hoare_logic). It does not have a good memory management story, as far as I know, but is very good for demonstrating value correctness (RTE automatically generates assertions for numeric runtime errors, for example) and many memory errors.
If you are familiar with Ada, check out SPARK (https://www.adacore.com/about-spark), which is similar to Frama-C but has a much better interface in the AdaCore GNAT toolkit and IDE.
Both work similarly: Assertions in normal Ada or C code as well as the code itself are translated into SMT statements and fed to a SMT solver to find counterexamples---errors.
I have some blog posts from several years ago about Frama-C:https://maniagnosis.crsr.net/tags/applied%20formal%20logic.h... (And I really should get back into it; it's a lot of fun.)
If you are not familiar with Ada or C, Dafny (https://dafny.org/) is another option based on .NET and devoleped at Microsoft. It seems nigh-on perfect for this approach. (The language uses a garbage collector.) At the time I was looking, there was little documentation on Dafny, but that seems to have improved.
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Thoughts on proof assistants?
But I suspect that will improve (they're all very new projects). I'm also keeping an eye on Dafny which looks pretty neat and avoids the "oh sorry we don't support traits" issue.
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What is the toughest concept to understand and implement in .NET according to you?
However, if you want the full-fledged powerful code contacts back, you have to go outside C#. The closest you'll get is Dafny. It is a spec language that compiles to C#.
SharpLab
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The One Billion Row Challenge – .NET Edition
One results in MOVSX, the other in MOVZX [1]. The difference thus is sign/zero extension when moving to the larger register. However, they seem to perform pretty much identical if I'm reading Agner Fog's instruction tables correctly.
[1] https://sharplab.io/#v2:C4LghgzgtgPgAgJgIwFgBQcDMACR2DC2A3ut...
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Any programs or websites to practice programming?
If you don't have an IDE, you can use SharpLab.io or dotnet fiddle
- Por debaixo do capô: async/await e as mágicas do compilador csharp
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C# Testing Playgrounds for old versions?
The closest online tool I can think of would be SharpLab, but you can only choose between Roslyn's git branches instead of C# versions.
- The combined power of F# and C#
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TypeScript 5.2's New Keyword: 'using'
> C# doesn't allow you to destructure a single property and as far as I can tell
https://sharplab.io/#v2:C4LgTgrgdgNAJiA1AHwAICYAMBYAUBgRj2Nw...
Your code is destructuring two properties and discarding one of them. It doesn't work with a single property: https://sharplab.io/#v2:C4LgTgrgdgNAJiA1AHwAICYAMBYAUBgRj2Nw...
I think that records don't generate a deconstruct method when they only have one property, but even if you manually define one you'll get an error on `var (varName) = ...`
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Tips for entry-level .net developer?
- LinqPad is great and I love, but, IMO, it is not the best tool to start with. It does not provide intellisense or debugger in the free version. Assuming you do not want to pay for this licence just to play a little with the language, I'd suggest https://sharplab.io/. It is not as powerfull as LinqPad, but at least it gives you suggestions.
- Running a XUnit test with C#?
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C# courses that take a look at how the language runs under the hood?
And you should checkout https://sharplab.io/ to see what IL, assembly is generated for whatever code.
What are some alternatives?
JITWatch - Log analyser / visualiser for Java HotSpot JIT compiler. Inspect inlining decisions, hot methods, bytecode, and assembly. View results in the JavaFX user interface.
Roslyn - The Roslyn .NET compiler provides C# and Visual Basic languages with rich code analysis APIs.
tlaplus - TLC is a model checker for specifications written in TLA+. The TLA+Toolbox is an IDE for TLA+.
.NET Runtime - .NET is a cross-platform runtime for cloud, mobile, desktop, and IoT apps.
BenchmarkDotNet - Powerful .NET library for benchmarking
FStar - A Proof-oriented Programming Language
interactive - .NET Interactive combines the power of .NET with many other languages to create notebooks, REPLs, and embedded coding experiences. Share code, explore data, write, and learn across your apps in ways you couldn't before.
rust - Rust for the xtensa architecture. Built in targets for the ESP32 and ESP8266
koka - Koka language compiler and interpreter
Rust-for-Linux - Adding support for the Rust language to the Linux kernel.
csharplang - The official repo for the design of the C# programming language
ASP.NET Core - ASP.NET Core is a cross-platform .NET framework for building modern cloud-based web applications on Windows, Mac, or Linux.