Improve lisp (#455)

* Replace car and cdr builtins with head and tail

* Add nth function

* Reorder core functions

* Rename uniq to unique

* Add list test

* Update doc

* Update examples

* Remove abs definition from example

* Fix tests

* Fix rest

doc/lisp.md

@@ -50,8 +50,8 @@ Rewrite parts of the code and add new functions and examples.
 - `splice` (with the `@` syntax)
 - `atom` (aliased to `atom?`)
 - `eq` (aliased to `eq?`)
-- `car` (aliased to `first`)
-- `cdr` (aliased to `rest`)
+- `head` (aliased to `car`)
+- `tail` (aliased to `cdr`)
 - `cons`
 - `if`
 - `cond`
@@ -78,12 +78,13 @@ Rewrite parts of the code and add new functions and examples.
 - `regex-find`
 - `system`
 
-- Arithmetic operations: `+`, `-`, `*`, `/`, `%`, `^`
+- Arithmetic operations: `+`, `-`, `*`, `/`, `%`, `^`, `abs`
 - Trigonometric functions: `acos`, `asin`, `atan`, `cos`, `sin`, `tan`
 - Comparisons: `>`, `<`, `>=`, `<=`, `=`
 - File IO: `read-file`, `read-file-bytes`, `write-file-bytes`, `append-file-bytes`
-- List: `chunks`, `slice`, `sort`, `uniq`, `length`
+- List: `chunks`, `sort`, `unique`, `min`, `max`
 - String: `trim`, `split`
+- Enumerable: `length`, `nth`, `first`, `second`, `third`, `last`, `rest`, `slice`
 
 ### Core Library
 - `nil`, `nil?`, `eq?`
@@ -125,7 +126,7 @@ with the following content:
 
 (println
   (if (nil? args) "Usage: fibonacci <num>"
-    (fibonacci (string->number (car args)))))
+    (fibonacci (string->number (head args)))))
 ```
 
 Would produce the following output:

dsk/lib/lisp/alias.lsp

@@ -13,7 +13,11 @@
 (define def-fun
   (macro args `(define-function ,@args)))
 
-(define len length)
+(define (car lst)
+  (head lst))
+
+(define (cdr lst)
+  (tail lst))
 
 (define label
   (macro args `(define ,@args)))

dsk/lib/lisp/core.lsp

@@ -44,62 +44,47 @@
 (define-macro (let params values body)
   `((function ,params ,body) ,@values))
 
-(define (caar x)
-  (car (car x)))
-
-(define (cadr x)
-  (car (cdr x)))
-
-(define (cdar x)
-  (cdr (car x)))
-
-(define (cddr x)
-  (cdr (cdr x)))
-
-(define (rest x)
-  (cdr x))
-
-(define (first x)
-  (car x))
-
-(define (second x)
-  (first (rest x)))
-
-(define (third x)
-  (second (rest x)))
-
 (define (reduce f ls)
-  (if (nil? (rest ls)) (first ls)
-    (f (first ls) (reduce f (rest ls)))))
+  (if (nil? (tail ls)) (head ls)
+    (f (head ls) (reduce f (tail ls)))))
 
 (define (map f ls)
   (if (nil? ls) nil
     (cons
-      (f (first ls))
-      (map f (rest ls)))))
+      (f (head ls))
+      (map f (tail ls)))))
 
 (define (filter f ls)
   (if (nil? ls) nil
-    (if (f (first ls))
-      (cons (first ls) (filter f (rest ls)))
-      (filter f (rest ls)))))
+    (if (f (head ls))
+      (cons (head ls) (filter f (tail ls)))
+      (filter f (tail ls)))))
 
 (define (intersection a b)
   (filter (function (x) (contains? b x)) a))
 
 (define (reverse x)
   (if (nil? x) x
-    (append (reverse (rest x)) (cons (first x) '()))))
+    (append (reverse (tail x)) (cons (head x) '()))))
 
 (define (range i n)
   (if (= i n) nil
     (append (list i) (range (+ i 1) n))))
 
+(define (min lst)
+  (head (sort lst)))
+
+(define (max lst)
+  (head (reverse (sort lst))))
+
+(define (abs x)
+  (if (> x 0) x (- x)))
+
 (define (string-join ls s)
   (reduce (function (x y) (string x s y)) ls))
 
 (define (read-line)
-  (bytes->string (reverse (rest (reverse (read-file-bytes "/dev/console" 256))))))
+  (bytes->string (reverse (tail (reverse (read-file-bytes "/dev/console" 256))))))
 
 (define (read-char)
   (bytes->string (read-file-bytes "/dev/console" 4)))
@@ -135,3 +120,33 @@
 
 (define (chars contents)
   (split contents ""))
+
+(define (first lst)
+  (nth lst 0))
+
+(define (second lst)
+  (nth lst 1))
+
+(define (third lst)
+  (nth lst 2))
+
+(define (last lst)
+  (nth lst
+    (if (= (length lst) 0) 0 (- (length lst) 1))))
+
+(define (caar x)
+  (car (car x)))
+
+(define (cadr x)
+  (car (cdr x)))
+
+(define (cdar x)
+  (cdr (car x)))
+
+(define (cddr x)
+  (cdr (cdr x)))
+
+(define rest cdr)
+(define len length)
+(define rev reverse)
+(define uniq unique)

dsk/tmp/lisp/factorial.lsp

@@ -9,4 +9,4 @@
 
 (println
   (if (nil? args) "Usage: factorial <num>"
-    (factorial (string->number (car args)))))
+    (factorial (string->number (head args)))))

dsk/tmp/lisp/fibonacci.lsp

@@ -6,4 +6,4 @@
 
 (println
   (if (nil? args) "Usage: fibonacci <num>"
-    (fibonacci (string->number (car args)))))
+    (fibonacci (string->number (head args)))))

dsk/tmp/lisp/geotime.lsp

@@ -21,9 +21,6 @@
       (/ (* 2 pi) 365.0)
       (+ (days timestamp) (/ (- (hours timestamp) 12.0) 24.0))))))
 
-(define (abs x)
-  (if (< x 0) (- x) x))
-
 (define (pad x)
   (string (if (< x 10) "0" "") x))
 

dsk/tmp/lisp/pi.lsp

@@ -31,4 +31,4 @@
 
 (println
   (if (nil? args) "Usage: pi <precision>"
-    (pi-digits (string->number (car args)))))
+    (pi-digits (string->number (head args)))))

dsk/tmp/lisp/sum.lsp

@@ -5,4 +5,4 @@
 
 (println
   (if (nil? args) "Usage: sum <num>"
-    (sum (string->number (car args)) 0)))
+    (sum (string->number (head args)) 0)))

src/usr/lisp/env.rs

@@ -59,8 +59,9 @@ pub fn default_env() -> Rc<RefCell<Env>> {
     data.insert("number-type".to_string(),       Exp::Primitive(primitive::lisp_number_type));
     data.insert("parse".to_string(),             Exp::Primitive(primitive::lisp_parse));
     data.insert("list".to_string(),              Exp::Primitive(primitive::lisp_list));
-    data.insert("uniq".to_string(),              Exp::Primitive(primitive::lisp_uniq));
     data.insert("sort".to_string(),              Exp::Primitive(primitive::lisp_sort));
+    data.insert("unique".to_string(),            Exp::Primitive(primitive::lisp_unique));
+    data.insert("nth".to_string(),               Exp::Primitive(primitive::lisp_nth));
     data.insert("contains?".to_string(),         Exp::Primitive(primitive::lisp_contains));
     data.insert("slice".to_string(),             Exp::Primitive(primitive::lisp_slice));
     data.insert("chunks".to_string(),            Exp::Primitive(primitive::lisp_chunks));

src/usr/lisp/eval.rs

@@ -35,7 +35,7 @@ fn eval_eq_args(args: &[Exp], env: &mut Rc<RefCell<Env>>) -> Result<Exp, Err> {
     Ok(Exp::Bool(a == b))
 }
 
-fn eval_car_args(args: &[Exp], env: &mut Rc<RefCell<Env>>) -> Result<Exp, Err> {
+fn eval_head_args(args: &[Exp], env: &mut Rc<RefCell<Env>>) -> Result<Exp, Err> {
     ensure_length_eq!(args, 1);
     match eval(&args[0], env)? {
         Exp::List(list) => {
@@ -46,7 +46,7 @@ fn eval_car_args(args: &[Exp], env: &mut Rc<RefCell<Env>>) -> Result<Exp, Err> {
     }
 }
 
-fn eval_cdr_args(args: &[Exp], env: &mut Rc<RefCell<Env>>) -> Result<Exp, Err> {
+fn eval_tail_args(args: &[Exp], env: &mut Rc<RefCell<Env>>) -> Result<Exp, Err> {
     ensure_length_eq!(args, 1);
     match eval(&args[0], env)? {
         Exp::List(list) => {
@@ -149,7 +149,7 @@ pub fn eval_args(args: &[Exp], env: &mut Rc<RefCell<Env>>) -> Result<Vec<Exp>, E
 
 pub const BUILT_INS: [&str; 32] = [
     "quote", "quasiquote", "unquote", "unquote-splicing",
-    "atom", "eq", "car", "cdr", "cons",
+    "atom", "eq", "head", "tail", "cons",
     "if", "cond", "while",
     "set",
     "define", "def", "label",
@@ -180,8 +180,8 @@ pub fn eval(exp: &Exp, env: &mut Rc<RefCell<Env>>) -> Result<Exp, Err> {
                     Exp::Sym(s) if s == "quote"  => return eval_quote_args(args),
                     Exp::Sym(s) if s == "atom"   => return eval_atom_args(args, env),
                     Exp::Sym(s) if s == "eq"     => return eval_eq_args(args, env),
-                    Exp::Sym(s) if s == "car"    => return eval_car_args(args, env),
-                    Exp::Sym(s) if s == "cdr"    => return eval_cdr_args(args, env),
+                    Exp::Sym(s) if s == "head"   => return eval_head_args(args, env),
+                    Exp::Sym(s) if s == "tail"   => return eval_tail_args(args, env),
                     Exp::Sym(s) if s == "cons"   => return eval_cons_args(args, env),
                     Exp::Sym(s) if s == "set"    => return eval_set_args(args, env),
                     Exp::Sym(s) if s == "while"  => return eval_while_args(args, env),

src/usr/lisp/mod.rs

@@ -336,13 +336,13 @@ fn test_lisp() {
     assert_eq!(eval!("(eq 1 1.0)"), "false");
     assert_eq!(eval!("(eq 1.0 1.0)"), "true");
 
-    // car
-    assert_eq!(eval!("(car (quote (1)))"), "1");
-    assert_eq!(eval!("(car (quote (1 2 3)))"), "1");
+    // head
+    assert_eq!(eval!("(head (quote (1)))"), "1");
+    assert_eq!(eval!("(head (quote (1 2 3)))"), "1");
 
-    // cdr
-    assert_eq!(eval!("(cdr (quote (1)))"), "()");
-    assert_eq!(eval!("(cdr (quote (1 2 3)))"), "(2 3)");
+    // tail
+    assert_eq!(eval!("(tail (quote (1)))"), "()");
+    assert_eq!(eval!("(tail (quote (1 2 3)))"), "(2 3)");
 
     // cons
     assert_eq!(eval!("(cons (quote 1) (quote (2 3)))"), "(1 2 3)");
@@ -484,6 +484,7 @@ fn test_lisp() {
     eval!("(define x 'a)");
     assert_eq!(eval!("`(x ,x y)"), "(x a y)");
     assert_eq!(eval!("`(x ,x y ,(+ 1 2))"), "(x a y 3)");
+    assert_eq!(eval!("`(list ,(+ 1 2) 4)"), "(list 3 4)");
 
     // unquote-splice
     eval!("(define x '(1 2 3))");

src/usr/lisp/primitive.rs

@@ -51,12 +51,12 @@ pub fn lisp_add(args: &[Exp]) -> Result<Exp, Err> {
 pub fn lisp_sub(args: &[Exp]) -> Result<Exp, Err> {
     ensure_length_gt!(args, 0);
     let args = list_of_numbers(args)?;
-    let car = args[0].clone();
+    let head = args[0].clone();
     if args.len() == 1 {
-        Ok(Exp::Num(-car))
+        Ok(Exp::Num(-head))
     } else {
         let res = args[1..].iter().fold(Number::Int(0), |acc, a| acc + a.clone());
-        Ok(Exp::Num(car - res))
+        Ok(Exp::Num(head - res))
     }
 }
 
@@ -71,8 +71,8 @@ pub fn lisp_div(args: &[Exp]) -> Result<Exp, Err> {
             return Err(Err::Reason("Division by zero".to_string()));
         }
     }
-    let car = args[0].clone();
-    let res = args[1..].iter().fold(car, |acc, a| acc / a.clone());
+    let head = args[0].clone();
+    let res = args[1..].iter().fold(head, |acc, a| acc / a.clone());
     Ok(Exp::Num(res))
 }
 
@@ -84,16 +84,16 @@ pub fn lisp_mod(args: &[Exp]) -> Result<Exp, Err> {
             return Err(Err::Reason("Division by zero".to_string()));
         }
     }
-    let car = args[0].clone();
-    let res = args[1..].iter().fold(car, |acc, a| acc % a.clone());
+    let head = args[0].clone();
+    let res = args[1..].iter().fold(head, |acc, a| acc % a.clone());
     Ok(Exp::Num(res))
 }
 
 pub fn lisp_exp(args: &[Exp]) -> Result<Exp, Err> {
     ensure_length_gt!(args, 0);
     let args = list_of_numbers(args)?;
-    let car = args[0].clone();
-    let res = args[1..].iter().fold(car, |acc, a| acc.pow(a));
+    let head = args[0].clone();
+    let res = args[1..].iter().fold(head, |acc, a| acc.pow(a));
     Ok(Exp::Num(res))
 }
 
@@ -311,7 +311,7 @@ pub fn lisp_list(args: &[Exp]) -> Result<Exp, Err> {
     Ok(Exp::List(args.to_vec()))
 }
 
-pub fn lisp_uniq(args: &[Exp]) -> Result<Exp, Err> {
+pub fn lisp_unique(args: &[Exp]) -> Result<Exp, Err> {
     ensure_length_eq!(args, 1);
     if let Exp::List(list) = &args[0] {
         let mut list = list.clone();
@@ -342,6 +342,28 @@ pub fn lisp_contains(args: &[Exp]) -> Result<Exp, Err> {
     }
 }
 
+pub fn lisp_nth(args: &[Exp]) -> Result<Exp, Err> {
+    ensure_length_eq!(args, 2);
+    let i = usize::try_from(number(&args[1])?)?;
+    match &args[0] {
+        Exp::List(l) => {
+            if let Some(e) = l.iter().nth(i) {
+                Ok(e.clone())
+            } else {
+                Ok(Exp::List(Vec::new()))
+            }
+        }
+        Exp::Str(s) => {
+            if let Some(c) = s.chars().nth(i) {
+                Ok(Exp::Str(c.to_string()))
+            } else {
+                Ok(Exp::Str("".to_string()))
+            }
+        }
+        _ => Err(Err::Reason("Expected first arg to be a list or a string".to_string()))
+    }
+}
+
 pub fn lisp_slice(args: &[Exp]) -> Result<Exp, Err> {
     let (a, b) = match args.len() {
         2 => (usize::try_from(number(&args[1])?)?, 1),
@@ -357,7 +379,7 @@ pub fn lisp_slice(args: &[Exp]) -> Result<Exp, Err> {
             let s: String = s.chars().skip(a).take(b).collect();
             Ok(Exp::Str(s))
         }
-        _ => Err(Err::Reason("Expected first arg to be a list or a number".to_string()))
+        _ => Err(Err::Reason("Expected first arg to be a list or a string".to_string()))
     }
 }