Continuing on to the next language in the book: Factor.

Factor is…strange, and often frustrating. Where Lua felt simple and easy, Factor feels simple but hard.

Its concatenative syntax looks clean, just a list of words written out in order, but reading it requires you to keep a mental stack in your head at all times, so you can predict what the code does.

Here’s what I learned:

Day One

• not functions, words
• pull and push onto the stack
• no operator precedence, the math words are applied in order like everything else
• whitespace is significant
• not anonymous functions: quotations
• `if` needs quotations as the true and false branches
• data pushed onto stack can become "out of reach" when more data gets pushed onto it (ex: store a string, and then a number, the number is all you can reach)
• the `.` word becomes critical, then, for seeing the result of operations without pushing new values on the stack
• also have shuffle words for just this purpose (manipulating the stack)
• help documentation crashes; no listing online for how to get word docs in listener (plenty for vocab help, but that doesn't help me)
• factor is really hard to google for

Day Two

• word definitions must list how many values they take from the stack and how many they put back
• names in those definitions are not args, since they are arbitrary (not used in the word code itself)
• named global vars: symbols (have get and set; aka getters and setters)
• standalone code imports NOTHING, have to pull in all needed vocabularies by hand
• really, really hate the factor documentation
• for example, claims strings implement the sequence protocol, but that's not exactly true...can't use "suffix" on a string, for example

Day Three

• not maps, TUPLES
• auto-magically created getters and setters for all
• often just use f for an empty value
• is nice to be able to just write out lists of functions and not have to worry about explicit names for their arguments all over the place
• floats can be an issue in tests without explicit casting (no types for functions, just values from the stack)
• lots of example projects (games, etc) in the extra/ folder of the factor install