diff --git a/data-structures/lists.scm b/data-structures/lists.scm
new file mode 100644
index 0000000..46dca47
--- /dev/null
+++ b/data-structures/lists.scm
@@ -0,0 +1,26 @@
+(define (rangeinc b e)
+  (cond
+    ((> b e) '())
+    (#t (cons b (rangeinc (+ 1 b) e)))))
+
+(define (less-than l n) (cond ((null? l) #t) ((<= n 0) #f) (#t (less-than (cdr l) (- n 1)))))
+(define (unit v) v)
+(define (aget key alist) (cdr (assoc key alist)))
+(define (aset key val alist)
+  (cond
+    ((null? alist) `((,key . ,val)))
+    ((eqv? (caar alist) key) (cons `(,key . ,val) (cdr alist))) ; found and updated
+    (#t (cons (car alist) (aset key val (cdr alist))))    ; continue to seek
+))
+
+(define (dedup l p c) 
+  (cond 
+    ((null? l) `(((str . ,p) (ctr . ,c)))) 
+    ((string=? p (car l)) (dedup (cdr l) p (+ c 1)))
+    (#t (cons `((str . ,p) (ctr . ,c)) (dedup (cdr l) (car l) 1)))
+))
+
+(define (dedup<=? d1 d2)
+  (<= (aget 'ctr d1) (aget 'ctr d2)))
+
+
diff --git a/data-structures/strings.scm b/data-structures/strings.scm
new file mode 100644
index 0000000..e0f671e
--- /dev/null
+++ b/data-structures/strings.scm
@@ -0,0 +1,18 @@
+;--- String manipulation
+
+(define (string-suffix? src suffix)
+  (let [(src-len (string-length src)) (suf-len (string-length suffix))]
+    (and 
+      (>= src-len  suf-len) 
+      (string=? suffix (substring src (- src-len suf-len) src-len))
+)))
+
+(define (string-prefix? src prefix)
+  (let [(src-len (string-length src)) (pref-len (string-length prefix))]
+    (and
+      (>= src-len pref-len)
+      (string=? prefix (substring src 0 pref-len))
+)))
+
+(define (string-contains? src elem) ; we use port logic to implement this one
+  (seek-until (open-input-string src) elem))
diff --git a/io/filesystem.scm b/io/filesystem.scm
new file mode 100644
index 0000000..c4e8fa1
--- /dev/null
+++ b/io/filesystem.scm
@@ -0,0 +1,13 @@
+(define (build-path p1 p2)
+  (format "~a~a~a" p1 (directory-separator) p2))
+
+(define (walk-rec path subpath)
+  (cond
+    ((null? subpath) '())
+    (#t (append (walk (build-path path (car subpath))) (walk-rec path (cdr subpath))))
+))
+
+(define (walk path)
+  (cond
+    ((file-directory? path) (walk-rec path (directory-list path)))
+    (#t (list path))))
diff --git a/io/ports.scm b/io/ports.scm
new file mode 100644
index 0000000..c8ed0ff
--- /dev/null
+++ b/io/ports.scm
@@ -0,0 +1,34 @@
+(define (marker-finder step not-found found port marker remaining)
+  (let [(r (get-char port))]
+    (cond
+      ((eof-object? r) (not-found))
+      ((char=? r (car remaining))
+        (step 
+          r 
+          (cond
+            ((null? (cdr remaining)) (found))
+            (#t (marker-finder step not-found found port marker (cdr remaining))))))
+      (#t (step r (marker-finder step not-found found port marker marker)))
+)))
+
+(define (read-until port marker)
+  (list->string 
+    (marker-finder
+      (lambda (e r) (cons e r))
+      (lambda () '())
+      (lambda () '())
+      port 
+      (string->list marker) 
+      (string->list marker)
+)))
+
+(define (seek-until port marker)
+  (marker-finder
+    (lambda (e r) r)
+    (lambda () #f)
+    (lambda () #t)
+    port
+    (string->list marker) 
+    (string->list marker)
+))
+