A lisp interpreter written in shell script. It's incomplete... very much so. There are very few commands defined. The key ones that are defined include:

• Various arithmetic functions (+, -, *, /)
• Various comparison operatores (<, >, <=, >=, =)
• let, let*
• lambda
• if

The next big things to add include define, some looping construct, cons, index, etc. That being said, what's there now is enough to show the general idea of the end goal. Simple programs can be written (as shown by the fibonacci example), which is enough to see how things work. Time to work on the project is limited and, combined with the extremely limited usefulness of the project, leads to the fact that it may never get much further.

All that being said, its been a very fun learning project so far. Specifically, it's taught me a lot about bash. I thought I was fairly proficient with it before all this, but there's a lot of edge cases to be understood. Well worth the time spent on it.

When using the

    set -u

setting to throw an error on undefined variables, the following

    declare -a emptyArray=()
    ${emptyArray[@]}

winds up throwing an error. However, the following can be used to "work around" the issue

    ${emptyArray[@]:+${emptyArray[@]}}

eval

• if Atom, return it (token to value)
• if Nil, return it (token to value)
• if List, eval first element, switch on result
• if Lambda, evaluate the rest of list and call lambda with args
• if Macro, call it with args (unevaluated)
• otherwise, error... nothing else it can be

• This is an implementation of a Lisp-1, meaning that functions and variables share the same namespace (like Scheme)

> ./lishp.sh examples/lambda.simple.lishp 
Sourced libraries!
Code read!
=================
((lambda (x y) 
         (+ x y))
  5 10)
=================
Parsed!
Environment setup!
Done!
=================
Integer :: 15
=================