To-Do
 1. Fractions
+2. Tests
 3. expression as unit's val
+4. Revisar reduce y pasar a map
+5. mk :m recurse down primero
 6. Going multiprocess
 7. Functions! Derivate! Integrate!


ctx=%{"f"=>"3", "f(x)"=>"x^2"}
Exun.eval_ast("f*f(1)",ctx)