feat: add combinators to handle text that is prefixed or suffixed (#33)

basic.go

@@ -229,3 +229,46 @@ func I(c Combinator[[]string], i int) Combinator[string] {
 		return rem, ext[i], nil
 	}
 }
+
+// Prefixed will firstly scan the input text for a defined prefix and discard it.
+// The remaining input text will be matched against the [Combinator] and returned
+// if successful. Both combinators must match.
+//
+//	chomp.Prefixed(
+//		chomp.Tag(`"`),
+//		chomp.Tag("Hello"))(`"Hello, World!"`)
+//	// (`, World!"`, "Hello", nil)
+func Prefixed(pre, c Combinator[string]) Combinator[string] {
+	return func(s string) (string, string, error) {
+		rem, _, err := pre(s)
+		if err != nil {
+			return rem, "", err
+		}
+
+		return c(rem)
+	}
+}
+
+// Suffixed will firstly scan the input text and match it against the [Combinator].
+// The remaining text will be scanned for a defined suffix and discarded. Both
+// combinators must match.
+//
+//	chomp.Suffixed(
+//		chomp.Tag(", "),
+//		chomp.Tag("Hello"))("Hello, World!")
+//	// ("World!", "Hello", nil)
+func Suffixed(suf, c Combinator[string]) Combinator[string] {
+	return func(s string) (string, string, error) {
+		rem, ext, err := c(s)
+		if err != nil {
+			return rem, "", err
+		}
+
+		rem, _, err = suf(rem)
+		if err != nil {
+			return rem, "", err
+		}
+
+		return rem, ext, nil
+	}
+}

basic_test.go

@@ -329,6 +329,26 @@ func TestI(t *testing.T) {
 	assert.Equal(t, "and", ext)
 }
 
+func TestPrefixed(t *testing.T) {
+	t.Parallel()
+
+	rem, ext, err := chomp.Prefixed(chomp.Tag(`"`), chomp.Tag("Hello"))(`"Hello, World"`)
+
+	require.NoError(t, err)
+	assert.Equal(t, `, World"`, rem)
+	assert.Equal(t, "Hello", ext)
+}
+
+func TestSuffixed(t *testing.T) {
+	t.Parallel()
+
+	rem, ext, err := chomp.Suffixed(chomp.Tag(","), chomp.Tag("Hello"))("Hello, World")
+
+	require.NoError(t, err)
+	assert.Equal(t, " World", rem)
+	assert.Equal(t, "Hello", ext)
+}
+
 func TestCombinatorError(t *testing.T) {
 	t.Parallel()