I had to model it in Python

before writing it in OCaml.

implementations/Python/canhasstr.py

@@ -0,0 +1,22 @@
+
+
+def f(string, start=0, acc=[]):
+    if start >= len(string):
+        return acc
+    if '[' == string[start]:
+        return [1] + f(string, start+1, acc)
+    if ']' == string[start]:
+        return [0] + f(string, start+1, acc)
+    if ' ' == string[start]:
+        return f(string, start+1, acc)
+    symbol, n = bar(string, start, start)
+    return [symbol] + f(string, n, acc)
+
+
+def bar(string, start, end):
+    if end >= len(string) or string[end] in '[] ':
+        return string[start:end], end
+    return bar(string, start, end+1)
+
+
+print(f("1[2[] 3]4"))