cons: iota: document, test, improve.

1 files changed, 32 insertions, 12 deletions

diff --git a/cppawk-include/cons-priv.h b/cppawk-include/cons-priv.h
index 55790d1..97d410d 100644
--- a/cppawk-include/cons-priv.h
+++ b/cppawk-include/cons-priv.h
@@ -786,23 +786,43 @@ function __butlast(__lst, __n,
   return (__i in __circbuf) ? __list_end(__circbuf[__i]) : __nil
 }
 
-function __iota(__from, __to, __step,
-                __i, __out)
+function __iota(__from, __to, __delta,
+                __out, __i, __val)
 {
   __out = __list_begin();
 
   if (__from < __to) {
-    if (!__present(__step))
-      __step = 1
-    if (__step > 0)
-      for (__i = __from; __i <= __to; __i += __step)
-        __out = __list_add(__out, __i)
+    if (!__present(__delta))
+      __delta = 1
+
+    if (__delta <= 0)
+      return __nil;
+
+    __i = 0
+    __val = __from
+
+    while (__val <= __to) {
+      __out = __list_add(__out, __val)
+      __i++
+      __val = __from + (__i * __delta)
+    }
+  } else if (__from > __to) {
+    if (!__present(__delta))
+      __delta = -1
+
+    if (__delta >= 0)
+      return __nil;
+
+    __i = 0
+    __val = __from
+
+    while (__val >= __to) {
+      __out = __list_add(__out, __val)
+      __i++
+      __val = __from + (__i * __delta)
+    }
   } else {
-    if (!__present(__step))
-      __step = -1
-    if (__step < 0)
-      for (__i = __from; __i >= __to; __i += __step)
-        __out = __list_add(__out, __i)
+    return __list(__from)
   }
 
   return __list_end(__out)