Cog Blog Speeding Up Terf, Squeak, Pharo and Croquet with a fast open-source Smalltalk VM Pat-a-cake, pat-a-cake Baker’s man, Build me a JIT as fast as you can… So how does one write a just-in-time compiler (or JIT for short)? First, why write a JIT? Essentially dynamic languages defer certain performance-critical computations to run-time. These languages are "late-bound". Type information is kept