"Leper" is a tiny Lisp-like written in Perl. It supports lambdas, conditional execution and quoting. It's lazy as hell; all work is deferred to thunks until demanded.
Function parameters can use sigils to denote the type they hold, which is type-checked at run time. Lepr uses functional scoping rules.
Lepr is mostly "pure"; set and print are the only forms which don't return a value. Looping is done via recursion, symbols once set cannot be re-defined. Here I was influenced by the book Introduction To Functional Programming (Bird & Wadler 1st ed.). It's difficult to match the elegance of ML without pattern matching but thanks to Lisp's syntax, Lepr is quite terse.
Peter Norvig's article on Lispy inspired me, I hope it inspires you too.
echo '(print "Hello, World!")' | ./lepr
Hello, World!
./lepr t/hello.lr
Hello, World!
Single line comments begin with ;.
- functions
- lists
- nums
- strings
- nil
The only false value is nil all other values are true. nil is equal to an empty list, so it is both an atom and a list.
Currently only supports the quote operator ' which is expanded into the quote keyword. E.g.
'(1 2 3) --> (quote (1 2 3))
(fun (params) form...)
(if cond then else)
(set key value ...)
(quote form...)
Function parameters may be prefaced with a sigil to denote its type:
@ list
* atom
& function
# num
$ str
The absence of a sigil means any type is permitted. Within the function body the sigil is not used when referring to the bound argument. E.g. here is a function which accepts a number and returns it:
(fun (#x) x)
print
atom (x)
cons (*x @l)
car (@l)
cdr (@l)
eq (x y)
++ (@l @m)
N.b. these satisfy the Lisp 1.5 elementary functions from the LISP 1.5 Programmer's Manual.
Binary numerical functions:
== (#x #y)
>= (#x #y)
<= (#x #y)
> (#x #y)
< (#x #y)
+ (#x #y)
- (#x #y)
/ (#x #y)
* (#x #y)
^ (#x #y)
% (#x #y)
These come from Lepr's std library:
(set id (fun (x) x)
&& (fun (x y) (if x y nil))
|| (fun (x y) (if x x y))
map (fun (&f @l)
(set h (car l) t (cdr l))
(cons (f h) (if t (map f t) '())))
grep (fun (&f @l)
(set h (car l) t (cdr l))
(++ (if (f h) (cons h '()) nil)
(if t (grep f t) nil)))
sort (fun (@nums)
(set h (car nums)
t (cdr nums)
lt (if t (grep (fun (#n) (< n h)) t) nil)
ge (if t (grep (fun (#n) (>= n h)) t) nil))
(if nums (++ (sort lt) (cons h (sort ge))) nil))
foldl (fun (&f i @l)
(set h (car l) t (cdr l))
(if l (foldl f (f i h) t) i))
and (fun (@l) (foldl && 1 l))
or (fun (@l) (foldl || nil l)))
Run the test suite:
$ t/run-tests.t
Perl 5.16 or higher.
Save the lepr file somewhere in your PATH.
Copyright 2020 David Farrell
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