cons: add ldiff, last and butlast.

2 files changed, 93 insertions, 5 deletions

diff --git a/cppawk-include/cons-priv.h b/cppawk-include/cons-priv.h
index 85bbe42..4c0a767 100644
--- a/cppawk-include/cons-priv.h
+++ b/cppawk-include/cons-priv.h
@@ -93,9 +93,13 @@
        !__endp(__g(i)) && ((item = __car(__g(i))) || 1);                      \
        __prog(__g(i) = __cdr(__g(i)), index++))
 
+#define __doconses(iter, list)                                                \
+  for (iter = list; __consp(iter); iter = __cdr(iter))
+
 #define __list_begin() ""
 #define __list_add(stk, item) __pack(stk, item)
-#define __list_end(stk) __unpack(stk)
+#define __list_end(stk) __unpack(stk, __nil)
+#define __list_end_atom(stk, atom) __unpack(stk, atom)
 
 #define __bag_init_first(x)   (x = __list_begin())
 #define __bag_init_next(p, x) (p || 1) && __bag_init_first(x)
@@ -417,11 +421,9 @@ function __pack(__stk, __item)
   return length(__item) ":" __item __stk
 }
 
-function __unpack(__stk,
-                  __col, __out)
+function __unpack(__stk, __out,
+                  __col)
 {
-  __out = __nil
-
   while (__stk != "") {
     __col = match(__stk, /:/)
     if (__col == 0)
@@ -701,6 +703,89 @@ function __nthcdr(__pos, __lst)
   return __lst
 }
 
+function __ldiff(__main, __tail,
+                 __out, __iter)
+{
+  if (__null(main))
+    return nil
+
+  if (__null(tail))
+    return __main
+
+  __out = __list_begin()
+
+  __doconses (__iter, __main) {
+    if (__iter == __tail)
+      break
+    __out = __list_add(__out, __car(__iter))
+  }
+
+  if (__atom(__iter) && __iter != __tail)
+      return __list_end_atom(__out, __iter)
+
+  return __list_end(__out)
+}
+
+function __last(__lst, __n,
+                __circbuf, __i)
+{
+  if (!__present(__n))
+    __n = 1
+  else if (__n < 0)
+    __error("last: number argument %s must be non-negative", __n)
+
+  if (__n == 0) {
+    __doconses (__iter, __lst)
+      ; // nothing
+    return __iter
+  }
+
+  delete __circbuf
+
+  __i = 0
+
+  __n++
+
+  __doconses (__iter, __lst)
+    __circbuf[__i++ % __n] = __iter
+
+  __i = (__i + 1) % __n
+
+  return (__i in __circbuf) ? __circbuf[__i] : __lst
+}
+
+function __butlast(__lst, __n,
+                   __circbuf, __i, __out)
+{
+  if (!__present(__n))
+    __n = 1
+  else if (__n < 0)
+    __error("butlast: number argument %s must be non-negative", __n)
+
+  __out = __list_begin()
+
+  if (__n == 0) {
+    __doconses (__iter, __lst)
+      __out = __list_add(__out, __car(__iter))
+    return __list_end(__out)
+  }
+
+  delete __circbuf
+
+  __i = 0
+
+  __n++
+
+  __doconses (__iter, __lst) {
+    __circbuf[__i++ % __n] = __out
+    __out = __list_add(__out, __car(__iter))
+  }
+
+  __i = (__i + 1) % __n
+
+  return (__i in __circbuf) ? __list_end(__circbuf[__i]) : __nil
+}
+
 function __iota(__from, __to, __step,
                 __i, __out)
 {
diff --git a/cppawk-include/cons.h b/cppawk-include/cons.h
index 0087930..2cf579f 100644
--- a/cppawk-include/cons.h
+++ b/cppawk-include/cons.h
@@ -78,6 +78,9 @@
 #define position __position
 #define nth __nth
 #define nthcdr __nthcdr
+#define ldiff __ldiff
+#define last __last
+#define butlast __butlast
 #define iota __iota
 #define uniq __uniq
 #define mapcar __mapcar