Merge pull request #2569 from actonlang/re-match-start-pos

Add start_pos to re.match

Author: plajjan

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Unreleased
 
 ### Added
+- `re.match()` now accepts an optional `start_pos` to begin scanning at an offset.
 - Add `acton doc` command for generating documentation [#2292]
   - Supports multiple output formats (text, markdown, HTML)
   - Default is to open browser into HTML docs when window environment is

base/src/re.act

@@ -43,11 +43,12 @@ class Match:
 def _match(pattern: str, string: str, start_pos: int) -> ?Match:
     NotImplemented
 
-def match(pattern: str, string: str) -> ?Match:
+def match(pattern: str, string: str, start_pos: int=0) -> ?Match:
     """Scan through string looking for a match to the pattern, returning
-    a match object, or None if no match was found.
+    a match object, or None if no match was found. start_pos sets the
+    index to begin scanning at.
     """
-    return _match(pattern, string, 0)
+    return _match(pattern, string, start_pos)
 
 def matches(pattern: str, string: str) -> list[Match]:
     """Find all non-overlapping matches in string

docs/acton-guide/src/stdlib/re.md

@@ -12,8 +12,10 @@ actor main(env):
     env.exit(0)
 ```
 
+`re.match` also accepts an optional `start_pos` to begin scanning at a
+specific index (defaults to 0).
+
 Output:
 ```sh
 Got a match: foobar
 ```
-

test/stdlib_tests/src/test_re.act

@@ -92,6 +92,25 @@ def _test_match_positions():
         # Also verify the substring matches what we expect
         testing.assertEqual(m.string[m.start_pos:m.end_pos], "def")
 
+def _test_match_start_pos():
+    """Test that start_pos controls where the search begins."""
+    s = "def def"
+
+    m1 = re.match("def", s)
+    testing.assertNotNone(m1, "Should have matched first 'def'")
+    if m1 is not None:
+        testing.assertEqual(m1.start_pos, 0)
+        testing.assertEqual(m1.end_pos, 3)
+
+    m2 = re.match("def", s, start_pos=4)
+    testing.assertNotNone(m2, "Should have matched second 'def' starting at index 4")
+    if m2 is not None:
+        testing.assertEqual(m2.start_pos, 4)
+        testing.assertEqual(m2.end_pos, 7)
+
+    m3 = re.match("def", s, start_pos=5)
+    testing.assertNone(m3, "start_pos should skip earlier matches")
+
 def _test_split_no_match():
     """Split: pattern does not match anywhere"""
     res = re.split("xyz", "abc def ghi")