OCaml-Lisp

A "Lisp Interpreter" (Not a complete "Lisp", its a barely minimal subset). Made in a weekend with OCaml, being my first "project" with functional programming. Being my first time with a new language and paradigm don't expect good code quality. There is a lot of improvements to be made, I don't know if im going to keep working on it.

The Subset:

• Numbers (integers only), Lists
• if <cond> <success> <failure>
• def <name> <value>
• lambda (<params>) <body>
• + (add) and * (multiply) operations for Numbers only

Try it:

Run dune exec ocaml-lisp to enter in a repl. Beware its full of errors, for example:

ocaml-lisp> ((lambda (x) (x)) 2 4)
Fatal error: exception Invalid_argument("List.iter2")

This crashes out the repl, The problem here is that there are more arguments being applied than the arity of the lambda, however because of poor code quality and structure this case isn't managed and thus crashes.

Some other examples (that do work as "expected"):

ocaml-lisp> def x h                 
# (special-form)
! Error: Unbound symbol: x

Here the error is that x is unbound at this point, and def isn't being applied (to be applied it requires to be the operand of a list): (op arg arg arg ...) A correct definition could be something like:

ocaml-lisp> (def x 1)
# (unit)
ocaml-lisp> x
# (number 1)

ocaml-lisp> print
# (native-function)
ocaml-lisp> (print 2)
(number 2)
# (unit)
ocaml-lisp> 2
# (number 2)

Notice how here (number 2) appears twice, when there's a # preceding the output is the REPL output, otherwise is stdout/print.

Lets define a function

ocaml-lisp> (lambda (x) x)
# (lambda)

Lets apply something to it

ocaml-lisp> ((lambda (x) x) 2)
# (number 2)

Simple identity function isn't it?

Functions require the parameter section to be a list:

ocaml-lisp> (lambda a a)
! Error: Function expects parameters (list) and body
ocaml-lisp> (lambda (a) a)
# (lambda)
ocaml-lisp> (lambda (a))
! Error: Function expects parameters (list) and body

Notice how again because of poor code quality and structure, it can't tell you what's exactly missing. In the second error it should tell you that the body is missing.

Now this isn't useful at all, save it to a binding so its useful:

ocaml-lisp> (def identity (lambda (a) a))
# (unit)
ocaml-lisp> identity
# (lambda)
ocaml-lisp> (identity 2)
# (number 2)

Finally I'll show you some if statements:

ocaml-lisp> if
# (special-form)
ocaml-lisp> (def a 1)
# (unit)
ocaml-lisp> (if a (* a 2) a)
# (number 2)
ocaml-lisp> (def a 0)
# (unit)
ocaml-lisp> (if a (* a 2) a)
# (number 0)

TBD?

There is a single TODO documented in the code. But in reality there are many more things to be done. For example: adding quote support, better code structure and organization, error handling, and many more.