Enhance SVGSerialize to use zero-padded frame numbers for consistent file sorting.

modules/IOUtils.tla

@@ -16,6 +16,8 @@
 
 LOCAL INSTANCE TLC
 LOCAL INSTANCE Integers
+LOCAL INSTANCE Sequences
+LOCAL INSTANCE SequencesExt
   (*************************************************************************)
   (* Imports the definitions from the modules, but doesn't export them.    *)
   (*************************************************************************)
@@ -126,4 +128,32 @@ IOEnv ==
 atoi(str) ==
   CHOOSE i \in Int : ToString(i) = str
 
+(***************************************************************************)
+(* Pads a natural number with leading zeros to achieve a specified width.  *)
+(*                                                                         *)
+(* This function converts a natural number to a string and pads it with    *)
+(* leading zeros if necessary to reach the specified width. If the         *)
+(* number's string representation is already equal to or longer than the   *)
+(* specified width, no padding is added.                                   *)
+(*                                                                         *)
+(* Parameters:                                                             *)
+(*   - n: The natural number to be padded (must be >= 0)                   *)
+(*   - width: The desired total width of the resulting string              *)
+(*                                                                         *)
+(* Examples:                                                               *)
+(*   zeroPadN(42, 5) = "00042"                                             *)
+(*   zeroPadN(123, 3) = "123"                                              *)
+(*   zeroPadN(7, 1) = "7"                                                  *)
+(*   zeroPadN(0, 4) = "0000"                                               *)
+(*                                                                         *)
+(* Note: Negative numbers are not supported and may produce unexpected     *)
+(* results.                                                                *)
+(*                                                                         *)
+(* Returns a sequence of characters representing the zero-padded number.   *)
+(***************************************************************************)
+zeroPadN(n, width) ==
+    LET s == ToString(n)
+        padLen == width - Len(s)
+        zeros == [i \in 1..padLen |-> "0"]
+    IN FoldLeft(LAMBDA acc, z: acc \o z, "", zeros) \o s
 ============================================================================

modules/SVG.tla

@@ -230,14 +230,16 @@ PointOnLine(from, to, segment) ==
 (*   SVGSerialize(SVGDoc(myElements, 0, 0, 800, 600, <<>>),               *)
 (*                "svg_frame_", TLCGet("level"))                          *)
 (*                                                                        *)
-(* This creates files like: svg_frame_1.svg,                              *)
-(*                          svg_frame_2.svg, etc.                         *)
+(* This creates files like: svg_frame_01.svg,                             *)
+(*                          svg_frame_02.svg, etc.                        *)
 (**************************************************************************)
 SVGSerialize(svg, frameNamePrefix, frameNumber) ==
     LET IO == INSTANCE IOUtils IN
     IO!Serialize(
         SVGElemToString(svg),
-        frameNamePrefix \o ToString(frameNumber) \o ".svg",
+        \* Construct the filename using the prefix and a zero-padded frame
+        \* number so that files sort correctly lexicographically.
+        frameNamePrefix \o IO!zeroPadN(frameNumber, 2) \o ".svg",
         [format |-> "TXT", charset |-> "UTF-8", 
          openOptions |-> <<"WRITE", "CREATE", "TRUNCATE_EXISTING">>])
 

tests/IOUtilsTests.tla

@@ -98,6 +98,15 @@ ASSUME AssertError(
            "The argument of atoi should be a string, but instead it is:\n\"foo\"", 
            atoi("foo"))
 
+\* Test zeroPadN function with various inputs
+ASSUME(AssertEq(zeroPadN(42, 5), "00042"))
+ASSUME(AssertEq(zeroPadN(123, 3), "123"))
+ASSUME(AssertEq(zeroPadN(7, 1), "7"))
+ASSUME(AssertEq(zeroPadN(0, 4), "0000"))
+ASSUME(AssertEq(zeroPadN(999, 2), "999"))
+ASSUME(AssertEq(zeroPadN(1000, 6), "001000"))
+ASSUME(AssertEq(zeroPadN(0, 1), "0"))
+
 ---------------------------------------------------------------------------------------------------------------------------
 
 ASSUME PrintT("IOUtilsTests!C")