DEV: Add an integer parsing operation for string.

std/strings.ucg

@@ -20,6 +20,7 @@ let ops = module {
        split_on=split_on,
        split_at=split_at,
        substr=substr,
+       parse_int=parse_int,
       }) {
     let len = import "std/lists.ucg".len(mod.str);
     let str = mod.str;
@@ -89,6 +90,36 @@ let ops = module {
         )
     );
 
+    let parse_int = module{
+        str = mod.str,
+        start = 0,
+        end = len,
+    } => (f.maybe{val=result}) {
+        let pkg = mod.pkg();
+        let f = import "std/functional.ucg";
+
+        let reducer = func(acc, char) => acc{
+            str = select (char, acc.str) => {
+                "1" = acc.str + char,
+                "2" = acc.str + char,
+                "3" = acc.str + char,
+                "4" = acc.str + char,
+                "5" = acc.str + char,
+                "6" = acc.str + char,
+                "7" = acc.str + char,
+                "8" = acc.str + char,
+                "9" = acc.str + char,
+                "0" = acc.str + char,
+            },
+        };
+        let num = reduce(
+            reducer, {counter = 0, str = ""}, mod.str).str;
+        let result = select (num != "", NULL) => {
+            true = int(num),
+            false = NULL,
+        };
+    };
+
     let substr = module{
         str = mod.str,
         start = 0,

std/tests/strings_test.ucg

@@ -51,4 +51,15 @@ assert t.equal{
 assert t.equal{
     left = str_class.substr{end=8}.str,
     right = "foo bar",
+};
+
+assert t.equal{
+    left = strings.ops{str="123"}.parse_int{}.unwrap(),
+    right = 123,
+};
+
+let str_int = strings.ops{str="123"};
+assert t.equal{
+    left = strings.ops{str="123 "}.parse_int{}.unwrap(),
+    right = 123,
 };