loop: Allow start value to be omitted

It is convenient to be able to do just:

loop i 5 {
	body
}

Where the start value is 0.

Signed-off-by: Steve Bennett <steveb@workware.net.au>

3 files changed, 28 insertions, 9 deletions

diff --git a/jim.c b/jim.c
index bd5a819..bfec675 100644
--- a/jim.c
+++ b/jim.c
@@ -12198,17 +12198,26 @@ static int Jim_LoopCoreCommand(Jim_Interp *interp, int argc, Jim_Obj *const *arg
     jim_wide incr = 1;
     Jim_Obj *bodyObjPtr;
 
-    if (argc != 5 && argc != 6) {
-        Jim_WrongNumArgs(interp, 1, argv, "var first limit ?incr? body");
+    if (argc < 4 || argc > 6) {
+        Jim_WrongNumArgs(interp, 1, argv, "var ?first? limit ?incr? body");
         return JIM_ERR;
     }
 
-    if (Jim_GetWideExpr(interp, argv[2], &i) != JIM_OK ||
-        Jim_GetWideExpr(interp, argv[3], &limit) != JIM_OK ||
-          (argc == 6 && Jim_GetWideExpr(interp, argv[4], &incr) != JIM_OK)) {
-        return JIM_ERR;
+    retval = Jim_GetWideExpr(interp, argv[2], &i);
+    if (argc > 4 && retval == JIM_OK) {
+        retval = Jim_GetWideExpr(interp, argv[3], &limit);
+    }
+    if (argc > 5 && retval == JIM_OK) {
+        Jim_GetWideExpr(interp, argv[4], &incr);
+    }
+    if (retval != JIM_OK) {
+        return retval;
+    }
+    if (argc == 4) {
+        limit = i;
+        i = 0;
     }
-    bodyObjPtr = (argc == 5) ? argv[4] : argv[5];
+    bodyObjPtr = argv[argc - 1];
 
     retval = Jim_SetVariable(interp, argv[1], Jim_NewIntObj(interp, i));
 
diff --git a/jim_tcl.txt b/jim_tcl.txt
index 1a2b18a..24ea60b 100644
--- a/jim_tcl.txt
+++ b/jim_tcl.txt
@@ -58,6 +58,7 @@ Changes since 0.80
 2. Many commands now accept "safe" integer expressions rather than simple integers:
    `loop`, `range`, `incr`, `string repeat`, `lrepeat`, `pack`, `unpack`, `rand`
 3. String and list indexes now accept integer expressions (<<_string_and_list_index_specifications,STRING AND LIST INDEX SPECIFICATIONS>>)
+4. `loop` can now omit start value
 
 Changes between 0.79 and 0.80
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -3068,7 +3069,7 @@ Also see `defer` as another mechanism for cleaning up at the end of a procedure.
 
 loop
 ~~~~
-+*loop* 'var first limit ?incr? body'+
++*loop* 'var ?first? limit ?incr? body'+
 
 Similar to `for` except simpler and possibly more efficient.
 If +'incr'+ is positive, the effect is, equivalent to:
@@ -3079,11 +3080,12 @@ If +'incr'+ is positive, the effect is, equivalent to:
 
 While if +'incr'+ is negative, the count is downwards.
 
+If +'first'+ is not specified, 0 is used.
 If +'incr'+ is not specified, 1 is used.
 Note that setting the loop variable inside the loop does not
 affect the loop count.
 
-Integer parameters may be any integer expression.
++'first'+, +'limit'+ and +'incr'+ may be any integer expression.
 
 lindex
 ~~~~~~
diff --git a/tests/loop.test b/tests/loop.test
index df9001b..c6144e0 100644
--- a/tests/loop.test
+++ b/tests/loop.test
@@ -75,6 +75,14 @@ test loop-1.10 {no exec infinite loop} {
     set a
 } {}
 
+test loop-1.11 {no start} {
+    set a {}
+    loop i  5 {
+        lappend a $i
+    }
+    set a
+} {0 1 2 3 4}
+
 test loop-2.1 {loop shimmering tests} {
     loop i 1 6 {
     }