Tests & doc for array-from, array-from*, array-set-from!

* test-suite/tests/arrays.test: tests for array-from, array-from*,
  array-set-from!

* doc/ref/api-compound.texi: document array-from, array-from*,
  array-set-from!.

doc/ref/api-compound.texi

@@ -1709,6 +1709,109 @@ base and stride for new array indices in @var{oldarray} data.  A few
 sample points are enough because @var{mapfunc} is linear.
 @end deffn
 
+
+@deffn {Scheme Procedure} array-ref array idx @dots{}
+@deffnx {C Function} scm_array_ref (array, idxlist)
+Return the element at @code{(idx @dots{})} in @var{array}.
+@end deffn
+
+@deffn {Scheme Procedure} array-from array idx @dots{}
+@deffnx {C Function} scm_array_from (array, idxlist)
+If the length of @var{idxlist} equals the rank @math{n} of
+@var{array}, return the element at @code{(idx @dots{})}, just like
+@code{(array-ref array idx @dots{})}. If, however, the length @math{k}
+of @var{idxlist} is shorter than @math{n}, then return the shared
+@math{(n-k)}-rank prefix cell of @var{array} given by @var{idxlist}.
+
+For example:
+
+@example
+@lisp
+(array-from #2((a b) (c d)) 0) @result{} #(a b)
+(array-from #2((a b) (c d)) 1) @result{} #(c d)
+(array-from #2((a b) (c d)) 1 1) @result{} d
+(array-from #2((a b) (c d))) @result{} #2((a b) (c d))
+@end lisp
+@end example
+
+@code{(apply array-from array indices)} is equivalent to
+
+@lisp
+(let ((len (length indices)))
+  (if (= (array-rank a) len)
+    (apply array-ref a indices)
+    (apply make-shared-array a
+           (lambda t (append indices t))
+           (drop (array-dimensions a) len))))
+@end lisp
+
+The name `from' comes from the J language.
+@end deffn
+
+@deffn {Scheme Procedure} array-from* array idx @dots{}
+@deffnx {C Function} scm_array_from_s (array, idxlist)
+Like @code{(array-from array idx @dots{})}, but return a 0-rank shared
+array if the length of @var{idxlist} matches the rank of
+@var{array}. This can be useful when using @var{ARRAY} as destination
+of copies.
+
+Compare:
+
+@example
+@lisp
+(array-from #2((a b) (c d)) 1 1) @result{} d
+(array-from* #2((a b) (c d)) 1) @result{} #0(d)
+(define a (make-array 'a 2 2))
+(array-fill! (array-from* a 1 1) 'b)
+a @result{} #2((a a) (a b)).
+(array-fill! (array-from a 1 1) 'b) @result{} error: not an array
+@end lisp
+@end example
+
+@code{(apply array-from* array indices)} is equivalent to
+
+@lisp
+(apply make-shared-array a
+  (lambda t (append indices t))
+  (drop (array-dimensions a) (length indices)))
+@end lisp
+@end deffn
+
+
+@deffn {Scheme Procedure} array-set-from! array x idx @dots{}
+@deffnx {C Function} scm_array_set_from_x (array, x, idxlist)
+If the length of @var{idxlist} equals the rank @math{n} of
+@var{array}, set the element at @code{(idx @dots{})} of @var{array} to
+@var{x}, just like @code{(array-set! array x idx @dots{})}. If,
+however, the length @math{k} of @var{idxlist} is shorter than
+@math{n}, then copy the @math{(n-k)}-rank array @var{x}
+into @math{(n-k)}-rank prefix cell of @var{array} given by
+@var{idxlist}. In this case, the last @math{(n-k)} dimensions of
+@var{array} and the dimensions of @var{x} must match exactly.
+
+This function returns the modified @var{array}.
+
+For example:
+
+@example
+@lisp
+(array-set-from! (make-array 'a 2 2) b 1 1) @result{} #2((a a) (a b))
+(array-set-from! (make-array 'a 2 2) #(x y) 1) @result{} #2((a a) (x y))
+@end lisp
+@end example
+
+@code{(apply array-set-from! array x indices)} is equivalent to
+
+@lisp
+(let ((len (length indices)))
+  (if (= (array-rank array) len)
+    (apply array-set! array x indices)
+    (array-copy! x (apply array-from array indices)))
+  array)
+@end lisp
+@end deffn
+
+
 @deffn {Scheme Procedure} shared-array-increments array
 @deffnx {C Function} scm_shared_array_increments (array)
 For each dimension, return the distance between elements in the root vector.

test-suite/tests/arrays.test

@@ -290,6 +290,115 @@
       (and (eqv? 5 (array-ref s2 1))
 	   (eqv? 8 (array-ref s2 2))))))
 
+
+;;;
+;;; array-from*
+;;;
+
+(with-test-prefix/c&e "array-from*"
+
+  (pass-if "vector I"
+    (let ((v (vector 1 2 3)))
+      (array-fill! (array-from* v 1) 'a)
+      (array-equal? v #(1 a 3))))
+
+  (pass-if "vector II"
+    (let ((v (vector 1 2 3)))
+      (array-copy! #(a b c) (array-from* v))
+      (array-equal? v #(a b c))))
+
+  (pass-if "array I"
+    (let ((a (list->array 2 '((1 2 3) (4 5 6)))))
+      (array-fill! (array-from* a 1 1) 'a)
+      (array-equal? a #2((1 2 3) (4 a 6)))))
+
+  (pass-if "array II"
+    (let ((a (list->array 2 '((1 2 3) (4 5 6)))))
+      (array-copy! #(a b c) (array-from* a 1))
+      (array-equal? a #2((1 2 3) (a b c)))))
+
+  (pass-if "array III"
+    (let ((a (list->array 2 '((1 2 3) (4 5 6)))))
+      (array-copy! #2((a b c) (x y z)) (array-from* a))
+      (array-equal? a #2((a b c) (x y z)))))
+
+  (pass-if "rank 0 array"
+    (let ((a (make-array 77)))
+      (array-fill! (array-from* a) 'a)
+      (array-equal? a #0(a)))))
+
+
+;;;
+;;; array-from
+;;;
+
+(with-test-prefix/c&e "array-from"
+
+  (pass-if "vector I"
+    (let ((v (vector 1 2 3)))
+      (equal? 2 (array-from v 1))))
+
+  (pass-if "vector II"
+    (let ((v (vector 1 2 3)))
+      (array-copy! #(a b c) (array-from v))
+      (array-equal? v #(a b c))))
+
+  (pass-if "array I"
+    (let ((a (list->array 2 '((1 2 3) (4 5 6)))))
+      (equal? 5 (array-from a 1 1))))
+
+  (pass-if "array II"
+    (let ((a (list->array 2 '((1 2 3) (4 5 6)))))
+      (array-copy! #(a b c) (array-from a 1))
+      (array-equal? a #2((1 2 3) (a b c)))))
+
+  (pass-if "array III"
+    (let ((a (list->array 2 '((1 2 3) (4 5 6)))))
+      (array-copy! #2((a b c) (x y z)) (array-from a))
+      (array-equal? a #2((a b c) (x y z)))))
+
+  (pass-if "rank 0 array"
+    (let ((a (make-array 77)))
+      (equal? (array-from a) 77))))
+
+
+;;;
+;;; array-set-from!
+;;;
+
+(with-test-prefix/c&e "array-set-from!"
+
+  (pass-if "vector I"
+    (let ((v (vector 1 2 3)))
+      (and (eq? v (array-set-from! v 'x 1))
+           (array-equal? v #(1 x 3)))))
+
+  (pass-if "vector II"
+    (let ((v (vector 1 2 3)))
+      (and (eq? v (array-set-from! (array-from v) #(a b c)))
+           (array-equal? v #(a b c)))))
+
+  (pass-if "array I"
+    (let ((a (list->array 2 '((1 2 3) (4 5 6)))))
+      (and (eq? a (array-set-from! a 'x 1 1))
+           (array-equal? a #2((1 2 3) (4 x 6))))))
+
+  (pass-if "array II"
+    (let ((a (list->array 2 '((1 2 3) (4 5 6)))))
+      (and (eq? a (array-set-from! a #(a b c) 1))
+           (array-equal? a #2((1 2 3) (a b c))))))
+
+  (pass-if "array III"
+    (let ((a (list->array 2 '((1 2 3) (4 5 6)))))
+      (and (eq? a (array-set-from! a #2((a b c) (x y z))))
+           (array-equal? a #2((a b c) (x y z))))))
+
+  (pass-if "rank 0 array"
+    (let ((a (make-array 77)))
+      (and (eq? a (array-set-from! a 99))
+           (array-equal? a #0(99))))))
+
+
 ;;;
 ;;; array-contents
 ;;;