diff --git a/std/lists.ucg b/std/lists.ucg
index 95a2e2a..8eea8cd 100644
--- a/std/lists.ucg
+++ b/std/lists.ucg
@@ -48,9 +48,9 @@ let tail = func(list) => reduce(
 ).tail;
 
 // Enumerates the provided list with optional start and step parameters for the
-// enumeration. Prodices a list of pairs with the numeration and the list item.
+// enumeration. Produces a list of pairs with the enumeration and the list item.
 //
-// enumerate{list=["a","b","c"]}.result == [[0, "a"], [1, "b"], [2, "c"]]
+// enumerate{list=["a","b","c"]} == [[0, "a"], [1, "b"], [2, "c"]]
 let enumerate = module{
     // Where to start the enumeration.
     start = 0,
@@ -104,6 +104,7 @@ let slice = module {
 };
 
 // zips two lists together.
+// The result list is only as long as the shortest list.
 //
 // zip{list1=[0,2,4],list2=[1,3,5]}.result == [[0, 1], [2, 3], [4, 5]]
 let zip = module{
diff --git a/std/strings.ucg b/std/strings.ucg
index adce034..03790ca 100644
--- a/std/strings.ucg
+++ b/std/strings.ucg
@@ -1,6 +1,8 @@
 let ops = module {
     str="",
 } => {
+    let len = import "std/lists.ucg".len(mod.str);
+
     let split_on = module{
         on=" ",
         str=mod.str,
@@ -35,4 +37,19 @@ let ops = module {
             mod.str
         )
     );
+
+    let substr = module{
+        str = mod.str,
+        start = 0,
+        end = len,
+    } => (result) {
+        let reducer = func(acc, char) => acc{
+            counter = acc.counter + 1,
+            str = select ((acc.counter >= mod.start) && (acc.counter <= mod.end)), acc.str, {
+                true = acc.str + char,
+            },
+        };
+        let result = reduce(
+            reducer, {counter = 0, str = ""}, mod.str).str;
+    };
 };
\ No newline at end of file
diff --git a/std/tests/strings_test.ucg b/std/tests/strings_test.ucg
index 85e2b2e..24af532 100644
--- a/std/tests/strings_test.ucg
+++ b/std/tests/strings_test.ucg
@@ -21,4 +21,24 @@ assert asserts.equal{
 assert asserts.equal{
     left = str_class.split_at(3),
     right = {left="foo", right=" bar"},
+};
+
+assert asserts.equal{
+    left = str_class.len,
+    right = 7,
+};
+
+assert asserts.equal{
+    left = str_class.substr{start=1},
+    right = "oo bar",
+};
+
+assert asserts.equal{
+    left = str_class.substr{end=5},
+    right = "foo ba",
+};
+
+assert asserts.equal{
+    left = str_class.substr{end=8},
+    right = "foo bar",
 };
\ No newline at end of file