add subsequence_match(str, subseq) utility function

src/string.cc

@@ -94,4 +94,21 @@ bool prefix_match(const String& str, const String& prefix)
     return true;
 }
 
+bool subsequence_match(const String& str, const String& subseq)
+{
+    auto it = str.begin();
+    for (auto& c : subseq)
+    {
+        if (it == str.end())
+            return false;
+        while (*it != c)
+        {
+            if (++it == str.end())
+                return false;
+        }
+        ++it;
+    }
+    return true;
+}
+
 }

src/string.hh

@@ -113,6 +113,7 @@ String to_string(const StronglyTypedNumber<RealType, ValueType>& val)
 }
 
 bool prefix_match(const String& str, const String& prefix);
+bool subsequence_match(const String& str, const String& subseq);
 
 }
 

src/unit_tests.cc

@@ -141,6 +141,11 @@ void test_string()
    kak_assert(prefix_match("tchou kanaky", "tchou kanaky"));
    kak_assert(prefix_match("tchou kanaky", "t"));
    kak_assert(not prefix_match("tchou kanaky", "c"));
+
+   kak_assert(subsequence_match("tchou kanaky", "tknky"));
+   kak_assert(subsequence_match("tchou kanaky", "knk"));
+   kak_assert(subsequence_match("tchou kanaky", "tchou kanaky"));
+   kak_assert(not subsequence_match("tchou kanaky", "tchou  kanaky"));
 }
 
 void test_keys()