sample-code: Add a super hacky format-string implementation using eval and fmt builtins

sample-code/fstring.cl

@@ -0,0 +1,32 @@
+
+fn f(__fmt: str) -> str {
+    let __out = "";
+    let __expr = "";
+    let __depth = 0;
+    for __c in chars(__fmt) {
+        match __c {
+            '{' => {
+                __depth += 1
+                if __depth <= 1 {
+                    continue
+                }
+            },
+            '}' => {
+                __depth -= 1
+                if __depth <= 0 {
+                    __out += fmt(eval(__expr))
+                    __expr = ""
+                    continue
+                }
+            },
+            ':' => if __depth == 1 {
+                __out += __expr + ": "
+            },
+            _ => {}
+        }
+        if __depth > 0 {
+            __expr += __c
+        } else __out += __c;
+    }
+    __out
+}