Micro lisp implementation for study.
$ make ulisp
$ ./ulisp
- quote ... quote symbol
- cons ... construct pair
- atom ... predicate to check if next s-expression is atom or not (i.e. pair)
- car ... return the 1st expression of pair
- cdr ... return the 2nd expression of pair
- cond ... conditional construct. syntax: (cond (pred1 conseq1) [(pred2 conseq2) ...])
- set ... set variable to current environment
- lambda ... construct anonymous function. symtax: (lambda (params) body1 [body2 ...])
There is no value, so you CAN NOT use number nor string.
$ ./ulisp
> (quote ulisp)
ulisp
> t
True
> (set (quote hello) (quote ulisp))
ulisp
> hello
ulisp
> (set (quote r) (lambda (x y) (cond ((atom x) y) (t (r (cdr x) (cons (car x) y))))))
(*applicable* (x y) (cond ((atom x) y) (t (r (cdr x) (cons (car x) y)))))
> (r (quote (a b c d e f)) ())
(f e d c b a)
>
You can quit REPL with Ctrl+D.
If you set *verbose-eval* non-nil value, each eval prints its evaluation process.
$ ./ulisp
> (set (quote *verbose-eval*) t)
True
> (set (quote map) (lambda (f xs) (cond
((atom xs) xs)
((quote else) (cons (f (car xs)) (map f (cdr xs)))))))
EVALUATE: (set (quote map) (lambda (f xs) (cond ((atom xs) xs) ((quote else) (cons (f (car xs)) (map f (cdr xs)))))))
| env.*verbose-eval*=True
| env.map=*applicable*
| env.t=True
| EVALUATE: (quote map)
| | env.*verbose-eval*=True
| | env.map=*applicable*
| | env.t=True
| \___ map
| EVALUATE: (lambda (f xs) (cond ((atom xs) xs) ((quote else) (cons (f (car xs)) (map f (cdr xs))))))
| | env.*verbose-eval*=True
| | env.map=*applicable*
| | env.t=True
| \___ *applicable*
\___ *applicable*
*applicable*
>
You can trun off this verbose print to set nil to *verbose-eval*.
> (set (quote *verbose-eval*) ()))
This work inspired heavily 小さな Lisp インタープリタ.
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