Added tail, take, and drop

library/collections/classes.lisp

@@ -38,6 +38,9 @@
    #:head#
    #:last
    #:last#
+   #:tail
+   #:take
+   #:drop
    #:index-elt
    #:index-elt#
    #:index-where
@@ -178,6 +181,8 @@ the front or back, depending on which is natural for the underlying data structu
 
 ;; TODO: Make it so that these must all be the proper KeyedCollection types as well
 (coalton-toplevel
+  ;; NOTE: In all cases, LinearCollection methods should return collections that don't
+  ;; share mutable state with the original.
   (define-class (LinearCollection :m)
     ;; Get elements from the collection
     (head
@@ -192,6 +197,15 @@ the front or back, depending on which is natural for the underlying data structu
     (last#
      "Return the last element of the collection, erroring if it does not exist."
      (:m :a -> :a))
+    (tail
+     "Return all except the first element of the collection."
+     (:m :a -> :m :a))
+    (take
+     "Return the first `n` elements of the collection."
+     (UFix -> :m :a -> :m :a))
+    (drop
+     "Return all except the first `n` elements of the collection."
+     (UFix -> :m :a -> :m :a))
     ;; Query the collection
     (index-elt
      "Return the index of the first occurence of `elt`, if it can be found."
@@ -209,7 +223,6 @@ the front or back, depending on which is natural for the underlying data structu
      "Return the first element matching a predicate function."
      ((:a -> Boolean) -> :m :a -> Optional :a))
     ;; Retrieve subsets of the collection.
-    ;; NOTE: In all cases, these should return collections that don't share mutable state with the original.
     (subseq
      "Extract the collection from `start` (inclusive) to `end` (exclusive)."
      (UFix -> UFix -> :m :a -> :m :a))
@@ -330,6 +343,9 @@ with that element. The second collection is empty if no element satisfied `pred`
     (define last l:last)
     (define (last# lst)
       (o:from-some "Attempted to retrieve last element of empty list." (l:last lst)))
+    (define tail l:tail)
+    (define take l:take)
+    (define drop l:drop)
     (define index-elt l:elemIndex)
     (define (index-elt# elt lst)
       (o:from-some "Cannot find element in list." (l:elemIndex elt lst)))

library/collections/immutable/list.lisp

@@ -104,12 +104,12 @@
       ((Cons x _) (Some x))
       ((Nil) None)))
 
-  (declare tail (List :a -> Optional (List :a)))
+  (declare tail (List :a -> List :a))
   (define (tail l)
     "Returns every element except the first in a list."
     (match l
-      ((Cons _ xs) (Some xs))
-      ((Nil) None)))
+      ((Cons _ xs) xs)
+      ((Nil) Nil)))
 
   (declare car (List :a -> :a))
   (define (car x)

library/collections/mutable/vector.lisp

@@ -364,8 +364,8 @@
       (let ((end-point (min end (length vec)))
             (new-length (- end-point start))
             (new-vec (with-capacity new-length)))
-        (for i in (iter:up-to new-length)
-          (set! i (index-unsafe (+ start i) vec) new-vec))
+        (for i in (iter:range-increasing 1 start end-point)
+          (push! (index-unsafe i vec) new-vec))
         new-vec)))
 
   (declare split-at-vec (UFix -> Vector :a -> Tuple (Vector :a) (Vector :a)))
@@ -569,6 +569,12 @@
     (define cln:head# head-unsafe)
     (define cln:last last)
     (define cln:last# last-unsafe)
+    (define (cln:tail vec)
+      (subseq-vec 1 (length vec) vec))
+    (define (cln:drop n vec)
+      (subseq-vec n (length vec) vec))
+    (define (cln:take n vec)
+      (subseq-vec 0 n vec))
     (define cln:index-elt find-elem)
     (define (cln:index-elt# elt vec)
       (opt:from-some "Cannot find element in vector." (find-elem elt vec)))

library/prelude.lisp

@@ -167,6 +167,9 @@
    #:head#
    #:last
    #:last#
+   #:tail
+   #:take
+   #:drop
    #:index-elt
    #:index-elt#
    #:index-where
@@ -225,6 +228,9 @@
    #:head#
    #:last
    #:last#
+   #:tail
+   #:take
+   #:drop
    #:index-elt
    #:index-elt#
    #:index-where
@@ -251,11 +257,8 @@
 
   (:import-from
    #:coalton-library/collections/immutable/list
-   #:tail
    #:singleton
    #:repeat
-   #:drop
-   #:take
    #:find
    #:fold
    #:foldr
@@ -269,11 +272,8 @@
    #:any
    #:split)
   (:export
-   #:tail
    #:singleton
    #:repeat
-   #:drop
-   #:take
    #:find
    #:fold
    #:foldr