implement skip/2, fix limit/2 to emit error on negative count

builtin.jq

@@ -77,19 +77,26 @@ def limit($n; g):
   elif $n == 0 then
     empty
   else
+    error("limit doesn't support negative count")
+  end;
+def skip($n; g):
+  if $n > 0 then
+    foreach g as $item (
+      $n;
+      . - 1;
+      if . < 0 then $item else empty end
+    )
+  elif $n == 0 then
     g
+  else
+    error("skip doesn't support negative count")
   end;
 def nth($n): .[$n];
 def nth($n; g):
-  if $n < 0 then
-    error("nth doesn't support negative indices")
+  if $n >= 0 then
+    first(skip($n; g))
   else
-    label $out |
-    foreach g as $item (
-      $n + 1;
-      . - 1;
-      if . <= 0 then $item, break $out else empty end
-    )
+    error("nth doesn't support negative index")
   end;
 
 def truncate_stream(f):

cli/test.yaml

@@ -4053,7 +4053,23 @@
     - 'nth(-1;.[])'
   input: '[]'
   error: |
-    error: nth doesn't support negative indices
+    error: nth doesn't support negative index
+
+- name: nth/2 function with infinite range
+  args:
+    - 'nth(range(3); range(infinite))'
+  input: 'null'
+  expected: |
+    0
+    1
+    2
+
+- name: nth/2 function with error
+  args:
+    - 'nth(1; 0,1,error)'
+  input: 'null'
+  expected: |
+    1
 
 - name: all/2 function in first/1 argument
   args:
@@ -4070,6 +4086,28 @@
   expected: |
     [0,1,2,0,1,2,3,4,5,6,7,8,9,10,11,12]
 
+- name: limit/2 function with negative count
+  args:
+    - 'limit(-1; range(3))'
+  input: 'null'
+  error: |
+    limit doesn't support negative count
+
+- name: skip/2 function
+  args:
+    - -c
+    - '[skip(0,3,5,7; range(5))]'
+  input: 'null'
+  expected: |
+    [0,1,2,3,4,3,4]
+
+- name: skip/2 function with negative count
+  args:
+    - 'skip(-1; range(3))'
+  input: 'null'
+  error: |
+    skip doesn't support negative count
+
 - name: all/0, any/0 functions
   args:
     - -c