Building a Four-Bar Linkage Mechanism Simulator in Haskell

Most developers know Haskell as a language for functional programming, type safety, compilers, parsers, and beautiful mathematical abstractions. But can Haskell also be used to build an interactive engineering simulator? That was the motivation behind my project: Four-Bar Mechanism Haskell Simulator Repository: https://github.com/mohammadijoo/Four-Bar-Mechanism-Haskell This project is a browser-backed desktop-style GUI application written in Haskell. It visualizes, classifies, and animates a planar four-bar linkage mechanism, which is one of the most classical mechanisms in mechanical engineering, kinematics, and machine design. The GUI is built with Threepenny-GUI , so the interface runs in a local browser window, while the mathematical model and mechanism logic remain written in Haskell. For me, the interesting part was not only drawing a moving linkage. It was about connecting mechanism design theory , computational geometry , and functional programming in one small educational simulator. What is a four-bar linkage? A four-bar linkage is a closed-loop mechanical system made from four rigid links connected by four revolute joints. In this project, the four links are: Symbol Name Description g Ground link Fixed distance between pivots A and B a Input link Rotating link from A to moving pivot C b Output link Link from fixed pivot B to moving pivot D f Floating link / coupler Link connecting moving pivots C and D The fixed pivots are placed at: A = ( 0 , 0 ) , B = ( g , 0 ) The input link rotates by angle α . Therefore, point C can be computed directly as: C = ( a cos α ,; a sin α ) Point D is more interesting. It must satisfy two geometric distance constraints: ∣ D − C ∣ = f ∣ D − B ∣ = b So the simulator solves the position of point D using a circle-intersection method. One circle is centered at C with radius f . The other circle is centered at B with radius b . Where those two circles intersect, the mechanism can close. That is the basic geometric heart of the sim