list, string: support any number of +/-n for index

It is especially convenient to add -1 for something like:

  lindex $list end-$BACK-1

or:

  string range $str $p $p+$len-1

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

3 files changed, 39 insertions, 8 deletions

diff --git a/jim.c b/jim.c
index 684905f..2ccd769 100644
--- a/jim.c
+++ b/jim.c
@@ -7815,16 +7815,17 @@ static int SetIndexFromAny(Jim_Interp *interp, Jim_Obj *objPtr)
         str = endptr;
     }
 
-    /* Now str may include or +<num> or -<num> */
-    if (*str == '+' || *str == '-') {
+    /* Now str may include any number of +<num> or -<num> */
+    while (*str == '+' || *str == '-') {
         int sign = (*str == '+' ? 1 : -1);
 
         idx += sign * jim_strtol(++str, &endptr);
-        if (str == endptr || *endptr) {
+        if (endptr == str) {
             goto badindex;
         }
         str = endptr;
     }
+
     /* The only thing left should be spaces */
     while (isspace(UCHAR(*str))) {
         str++;
diff --git a/jim_tcl.txt b/jim_tcl.txt
index 73615c6..328aaab 100644
--- a/jim_tcl.txt
+++ b/jim_tcl.txt
@@ -55,6 +55,7 @@ RECENT CHANGES
 Changes since 0.80
 ~~~~~~~~~~~~~~~~~~
 1. TIP 582, comments allowed in expressions
+2. Indexes may contain any number of +n, -n
 
 Changes between 0.79 and 0.80
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -655,17 +656,18 @@ The index may be one of the following forms:
     A simple integer, where '0' refers to the first element of the string
     or list.
 
-+integer+integer+ or::
-+integer-integer+::
-    The sum or difference of the two integers. e.g. +2+3+ refers to the 5th element.
++integer+integer?...?+ or::
++integer-integer?...?+::
+    The sum or difference of the two or more integers. e.g. +2+3-1+ refers to the 4th element.
     This is useful when used with (e.g.) +$i+1+ rather than the more verbose
     +[expr {$i+1\}]+
 
 +end+::
     The last element of the string or list.
 
-+end-integer+::
-    The 'nth-from-last' element of the string or list.
++end-integer?...?+::
+    The 'nth-from-last' element of the string or list. Again, one or more integers may
+    be added or subtracted. e.g. +end-3+1+
 
 COMMAND SUMMARY
 ---------------
diff --git a/tests/jim.test b/tests/jim.test
index eaef8aa..ba76879 100644
--- a/tests/jim.test
+++ b/tests/jim.test
@@ -1837,6 +1837,34 @@ test lindex-17.1 {no index} {
     lindex {a b c}
 } {a b c}
 
+test lindex-18.1 {multiple +n} {
+    lindex {a b c d e f g} 1+1+1
+} {d}
+
+test lindex-18.2 {multiple +n/-n} {
+    lindex {a b c d e f g} 1+2-1
+} {c}
+
+test lindex-18.3 {end + multiple +n/-n} {
+    lindex {a b c d e f g} end-1-1
+} {e}
+
+test lindex-18.3 {end + multiple +n/-n} {
+    lindex {a b c d e f g} end-3+1
+} {e}
+
+test lindex-18.4 {multiple +/- in error} -body {
+    lindex {a b c d e f g} 1-x+3
+} -returnCodes error -match glob -result "bad index*"
+
+test lindex-18.5 {multiple +/- in error} -body {
+    lindex {a b c d e f g} 2-1+4x
+} -returnCodes error -match glob -result "bad index*"
+
+test lindex-18.6 {multiple +/- in error} -body {
+    lindex {a b c d e f g} end-3x-1
+} -returnCodes error -match glob -result "bad index*"
+
 catch { unset lindex}
 catch { unset minus }