phase: 20.49 COMPLETE; 20.50 Flow+String minimal reps; 20.51 selfhost v0/v1 minimal (Option A/B); hv1-inline binop/unop/copy; docs + run_all + CURRENT_TASK -> 21.0

apps/std/string.hako

@@ -0,0 +1,52 @@
+// std.string (Ny) - Phase15 MVP
+// Usage:
+//   include "apps/std/string.hako"
+//   StdStringNy.string_length("abc"), StdStringNy.string_concat("a","b"),
+//   StdStringNy.string_slice("hello",1,4), StdStringNy.string_index_of("banana","na"), StdStringNy.string_equals("x","y")
+// Notes:
+//   - ASCII only; slice clamps [start,end)
+//   - index_of returns -1 when not found
+//   - Pure functions; no side effects
+
+static box StdStringNy {
+  // Return length of string s (Integer)
+  string_length(s) {
+    if s == null { return 0 }
+    return s.length()
+  }
+
+  // Concatenate two strings
+  string_concat(a, b) {
+    return a.concat(b)
+  }
+
+  // Slice string in [start, end) with simple clamping
+  string_slice(s, start, end) {
+    if s == null { return "" }
+    return s.substring(start, end)
+  }
+
+  // Return first index of substring (or -1)
+  string_index_of(s, sub) {
+    if s == null { return -1 }
+    if sub == null { return 0 }
+    local n, m, i
+    n = s.length()
+    m = sub.length()
+    if m == 0 { return 0 }
+    if n < m { return -1 }
+    i = 0
+    loop (i <= (n - m)) {
+      // Compare window
+      if s.substring(i, i + m) == sub { return i }
+      i = i + 1
+    }
+    return -1
+  }
+
+  // Return 1 if equal else 0 (Integer)
+  string_equals(a, b) {
+    if a == b { return 1 }
+    return 0
+  }
+}