diff --git a/tapl/mlish.rkt b/tapl/mlish.rkt
index 13e0c5c..89c2b33 100644
--- a/tapl/mlish.rkt
+++ b/tapl/mlish.rkt
@@ -16,6 +16,7 @@
 (provide (rename-out [ext-stlc:and and] [ext-stlc:#%datum #%datum]))
 (reuse [cons stlc:cons] nil isnil head tail [list stlc:list] List ~List List? #:from "stlc+cons.rkt")
 (provide (rename-out [stlc:list list] [stlc:cons cons]))
+(reuse ref deref := Ref #:from "stlc+box.rkt")
 
 ;; ML-like language
 ;; - top level recursive functions
@@ -428,9 +429,16 @@
       : τ_out)])
 (define-typed-syntax when
   [(_ test body ...)
-   #:with test- (⇑ test as Bool)
+;   #:with test- (⇑ test as Bool)
+   #:with [test- _] (infer+erase #'test)
    #:with [(body- _) ...] (infers+erase #'(body ...))
    (⊢ (when test- body- ...) : Unit)])
+(define-typed-syntax unless
+  [(_ test body ...)
+;   #:with test- (⇑ test as Bool)
+   #:with [test- _] (infer+erase #'test)
+   #:with [(body- _) ...] (infers+erase #'(body ...))
+   (⊢ (unless test- body- ...) : Unit)])
 
 ;; sync channels and threads
 (define-type-constructor Channel)
@@ -463,6 +471,13 @@
 (define-primop random : (→ Int Int))
 (define-primop integer->char : (→ Int Char))
 (define-primop string->number : (→ String Int))
+;(define-primop number->string : (→ Int String))
+(define-typed-syntax num->str #:export-as number->string
+ [(_ n)
+  #'(num->str n (ext-stlc:#%datum . 10))]
+ [(_ n rad)
+  #:with args- (⇑s (n rad) as Int)
+  (⊢ (number->string . args-) : String)])
 (define-primop string : (→ Char String))
 (define-primop sleep : (→ Int Unit))
 (define-primop string=? : (→ String String Bool))
@@ -533,11 +548,22 @@
    #:with [e- (ty)] (⇑ e as Vector)
    (⊢ (in-vector e-) : (Sequence ty))])
 
+(define-typed-syntax in-list
+  [(_ e)
+   #:with [e- (ty)] (⇑ e as List)
+   (⊢ (in-list e-) : (Sequence ty))])
+
+(define-typed-syntax in-lines
+  [(_ e)
+   #:with e- (⇑ e as String)
+   (⊢ (in-lines (open-input-string e-)) : (Sequence String))])
+
 (define-typed-syntax for
-  [(_ ([x:id e]...) body)
+  [(_ ([x:id e]...) b ... body)
    #:with ([e- (ty)] ...) (⇑s (e ...) as Sequence)
-   #:with [(x- ...) body- ty_body] (infer/ctx+erase #'([x : ty] ...) #'body)
-   (⊢ (for ([x- e-] ...) body-) : Unit)])
+   #:with [(x- ...) (b- ... body-) (ty_b ... ty_body)] 
+          (infers/ctx+erase #'([x : ty] ...) #'(b ... body))
+   (⊢ (for ([x- e-] ...) b- ... body-) : Unit)])
 (define-typed-syntax for*
   [(_ ([x:id e]...) body)
    #:with ([e- (ty)] ...) (⇑s (e ...) as Sequence)
@@ -563,6 +589,24 @@
    #:when (typecheck? #'ty_body #'ty_init)
    (⊢ (for/fold ([acc- init-]) ([x- e-] ...) body-) : ty_body)])
 
+(define-typed-syntax for/hash
+  [(_ ([x:id e]...) body)
+   #:with ([e- (ty)] ...) (⇑s (e ...) as Sequence)
+   #:with [(x- ...) body- (~× ty_k ty_v)] 
+          (infer/ctx+erase #'([x : ty] ...) #'body)
+   (⊢ (for/hash ([x- e-] ...) (let ([t body-]) (values (car t) (cadr t))))
+        : (Hash ty_k ty_v))])
+
+(define-typed-syntax for/sum
+  [(_ ([x:id e]... 
+       (~optional (~seq #:when guard) #:defaults ([guard #'#t])))
+      body)
+   #:with ([e- (ty)] ...) (⇑s (e ...) as Sequence)
+   #:with [(x- ...) (guard- body-) (_ ty_body)]
+          (infers/ctx+erase #'([x : ty] ...) #'(guard body))
+   #:when (Int? #'ty_body)
+   (⊢ (for/sum ([x- e-] ... #:when guard-) body-) : Int)])
+
 ; printing and displaying
 (define-typed-syntax printf
   [(_ str e ...)
@@ -615,7 +659,11 @@
 ;   (⊢ (hash->list e-)
       : (Sequence (× ty_k ty_v)))])
 
+; mutable hashes
 (define-typed-syntax hash
+  [(_ (~and tys {ty_key ty_val}))
+   #:when (brace? #'tys)
+   (⊢ (make-hash) : (Hash ty_key ty_val))]
   [(_ (~seq k v) ...)
    #:with ([k- ty_k] ...) (infers+erase #'(k ...))
    #:with ([v- ty_v] ...) (infers+erase #'(v ...))
@@ -623,11 +671,35 @@
    #:when (same-types? #'(ty_v ...))
    #:with ty_key (stx-car #'(ty_k ...))
    #:with ty_val (stx-car #'(ty_v ...))
-   (⊢ (make-immutable-hash (list (cons k- v-) ...)) : (Hash ty_key ty_val))])
-   
+   (⊢ (make-hash (list (cons k- v-) ...)) : (Hash ty_key ty_val))])
+(define-typed-syntax hash-set!
+  [(_ h k v)
+   #:with [h- (ty_key ty_val)] (⇑ h as Hash)
+   #:with [k- ty_k] (infer+erase #'k)
+   #:with [v- ty_v] (infer+erase #'v)
+   #:when (typecheck? #'ty_k #'ty_key)
+   #:when (typecheck? #'ty_v #'ty_val)
+   (⊢ (hash-set! h- k- v-) : Unit)])
+(define-typed-syntax hash-ref/tc #:export-as hash-ref
+  [(_ h k) #'(hash-ref/tc h k (ext-stlc:#%datum . #f))]
+  [(_ h k fail)
+   #:with [h- (ty_key ty_val)] (⇑ h as Hash)
+   #:with [k- ty_k] (infer+erase #'k)
+   #:when (typecheck? #'ty_k #'ty_key)
+   #:with (fail- _) (infer+erase #'fail) ; default val can be any
+   (⊢ (hash-ref h- k- fail-) : ty_val)])
+(define-typed-syntax hash-has-key?
+  [(_ h k)
+   #:with [h- (ty_key _)] (⇑ h as Hash)
+   #:with [k- ty_k] (infer+erase #'k)
+   #:when (typecheck? #'ty_k #'ty_key)
+   (⊢ (hash-has-key? h- k-) : Bool)])
+
 (define-base-type String-Port)
 (define-primop open-output-string : (→ String-Port))
 (define-primop get-output-string : (→ String-Port String))
+(define-primop string-upcase : (→ String String))
+
 (define-typed-syntax write-string/tc #:export-as write-string
  [(_ str out)
   #'(write-string/tc str out (ext-stlc:#%datum . 0) (string-length/tc str))]
@@ -659,8 +731,10 @@
 
 (define-primop fl+ : (→ Float Float Float))
 (define-primop fl* : (→ Float Float Float))
+(define-primop fl/ : (→ Float Float Float))
 (define-primop flceiling : (→ Float Float))
 (define-primop inexact->exact : (→ Float Int))
+(define-primop exact->inexact : (→ Int Float))
 (define-primop char->integer : (→ Char Int))
 (define-primop fx->fl : (→ Int Float))
 (define-typed-syntax quotient+remainder
@@ -669,3 +743,31 @@
    #:with y- (⇑ y as Int)
    (⊢ (call-with-values (λ () (quotient/remainder x- y-)) list)
       : (× Int Int))])
+(define-primop quotient : (→ Int Int Int))
+
+(define-typed-syntax set!
+ [(_ x:id e)
+  #:with [x- ty_x] (infer+erase #'x)
+  #:with [e- ty_e] (infer+erase #'e)
+  #:when (typecheck? #'ty_e #'ty_x)
+  (⊢ (set! x e-) : Unit)])
+
+(define-typed-syntax provide
+  [(_ x:id)
+   #:with [x- ty_x] (infer+erase #'x)
+   #:with x-ty (format-id #'x "~a-ty" #'x) ; TODO: use hash-code to generate this tmp
+   #'(begin
+       (provide x)
+       (define-type-alias x-ty ty_x)
+       (provide x-ty))])
+(define-typed-syntax require-typed
+  [(_ x:id #:from mod)
+   #:with x-ty (format-id #'x "~a-ty" #'x)
+   #:with y (generate-temporary #'x)
+   #'(begin
+       (require (rename-in (only-in mod x x-ty) [x y]))
+       (define-syntax x (make-rename-transformer (assign-type #'y #'x-ty))))])
+
+(define-base-type Regexp)
+(define-primop regexp-match : (→ Regexp String (List String)))
+(define-primop regexp : (→ String Regexp))
diff --git a/tapl/tests/mlish/fasta.mlish b/tapl/tests/mlish/fasta.mlish
index 813152f..51fdde2 100644
--- a/tapl/tests/mlish/fasta.mlish
+++ b/tapl/tests/mlish/fasta.mlish
@@ -143,10 +143,22 @@
    [R str ->   
     (random-fasta ">THREE Homo sapiens frequency\n" (* n 5) HOMOSAPIEN R)]))
 (check-type (proj res1 1) : String
- -> ">TWO IUB ambiguity codes\ntaaaWKatgWRattaNBttctNagggcgWt\n")
+ -> ">TWO IUB ambiguity codes\nattRtBtaDtatVataKatgaatcccgDtY\n")
+;taaaWKatgWRattaNBttctNagggcgWt\n")
 ;; should be cttBtatcatatgctaKggNcataaaSatg ?
-(proj res1 0)
 (check-type (proj res2 1) : String
  -> (string-append ">THREE Homo sapiens frequency\n"
-                   "agggctccaaatcataaagaggaatatattattacacgattagaaaccca\n"))
+      "atttgcggaaacgacaaatattaacacatcatcagagtaccataaaggga\n"
+      #;"agggctccaaatcataaagaggaatatattattacacgattagaaaccca\n"))
 ;; should be taaatcttgtgcttcgttagaagtctcgactacgtgtagcctagtgtttg ?
+(define (mk-fasta [n : Int] -> String)
+  (let 
+   ([res1 (repeat-fasta ">ONE Homo sapiens alu\n" (* n 2) +alu+)]
+    [res2 (random-fasta ">TWO IUB ambiguity codes\n" (* n 3) IUB 42)]
+    [res3
+     (match res2 with
+      [R str ->   
+       (random-fasta ">THREE Homo sapiens frequency\n" (* n 5) HOMOSAPIEN R)])])
+   (string-append res1 (proj res2 1) (proj res3 1))))
+(provide mk-fasta)
+(check-type (mk-fasta 100) : String)
diff --git a/tapl/tests/mlish/fibo.mlish b/tapl/tests/mlish/fibo.mlish
new file mode 100644
index 0000000..0871885
--- /dev/null
+++ b/tapl/tests/mlish/fibo.mlish
@@ -0,0 +1,17 @@
+#lang s-exp "../../mlish.rkt"
+(require "../rackunit-typechecking.rkt")
+
+(define (fib [n : Int] -> Int)
+  (cond [(< n 2) 1]
+        (else (+ (fib (- n 2)) (fib (sub1 n))))))
+
+(define (main [args : (Vector String)] -> Int)
+  (let ([n (if (= (vector-length args) 0)
+               1
+               (string->number (vector-ref args 0)))])
+    (fib n)))
+
+(check-type (main (vector "0")) : Int -> 1)
+(check-type (main (vector "1")) : Int -> 1)
+(check-type (main (vector "2")) : Int -> 2)
+(check-type (main (vector "22")) : Int -> 28657)
diff --git a/tapl/tests/mlish/hash.mlish b/tapl/tests/mlish/hash.mlish
new file mode 100644
index 0000000..2d8e32f
--- /dev/null
+++ b/tapl/tests/mlish/hash.mlish
@@ -0,0 +1,14 @@
+#lang s-exp "../../mlish.rkt"
+(require "../rackunit-typechecking.rkt")
+
+(define (main [argv : (Vector String)] -> Int)
+  (let* ([n (string->number (vector-ref argv 0))]
+         [hash
+          (for/hash ([i (in-range n)])
+            (let ([j (add1 i)])
+              (tup (number->string j 16) j)))])
+    (for/sum ([i (in-range 1 (add1 n))]
+               #:when (hash-ref hash (number->string i)))
+      1)))
+
+(check-type (main (vector "200000")) : Int -> 30999)
diff --git a/tapl/tests/mlish/knuc.mlish b/tapl/tests/mlish/knuc.mlish
new file mode 100644
index 0000000..1f73086
--- /dev/null
+++ b/tapl/tests/mlish/knuc.mlish
@@ -0,0 +1,65 @@
+#lang s-exp "../../mlish.rkt"
+(require "../rackunit-typechecking.rkt")
+
+(require-typed mk-fasta #:from "fasta.mlish")
+
+(define (all-counts [len : Int][dna : String] -> (Hash String (Ref Int)))
+  (let ([table (hash {String (Ref Int)})])
+    (for ([s (in-range (- (string-length dna) len) -1 -1)])
+      (let ([key (make-string len)])
+        (string-copy! key 0 dna s (+ s len))
+        (let* ([b (if (hash-has-key? table key)
+                      (hash-ref table key)
+                      (let ([b (ref 0)])
+                        (hash-set! table key b)
+                        b))])
+          (:= b (add1 (deref b))))))
+    table))
+
+;; (define (write-freqs table)
+;;   (let* ([content (hash-map table (lambda (k v) (cons k (unbox v))))]
+;;          [total (exact->inexact (apply + (map cdr content)))])
+;;     (for ([a (sort content > #:key cdr)])
+;;       (printf "~a ~a\n" 
+;;               (car a) 
+;;               (real->decimal-string (* 100 (/ (cdr a) total)) 3)))))
+
+#;(define (write-one-freq [table : (Hash String (Ref Int))][key : String] -> Unit)
+  (let ([cnt (hash-ref table key (box 0))])
+    (printf "~a\t~a\n" (unbox cnt) key)))
+
+(define dna
+  (let* ([in (mk-fasta 100000)]
+         ;; Skip to ">THREE ..."
+         [rst (head (tail (regexp-match (regexp ">THREE Homo sapiens frequency\n(.*)$") in)))])
+    (let ([s (open-output-string)])
+      ;; Copy everything but newlines to s:
+      (for ([l (in-lines rst)])
+        (write-string l s))
+      ;; Extract the string from s:
+      (string-upcase (get-output-string s)))))
+
+(check-type dna : String)
+
+(check-type (all-counts 1 dna) : (Hash String (Ref Int)))
+;; ;; 1-nucleotide counts:
+;; (write-freqs (all-counts 1 dna))
+;; (newline)
+
+(check-type (all-counts 2 dna) : (Hash String (Ref Int)))
+;; ;; 2-nucleotide counts:
+;; (write-freqs (all-counts 2 dna))
+;; (newline)
+
+;; Specific sequences:
+(check-type
+    (for/list ([seq (in-list (list "GGT" "GGTA" "GGTATT" 
+                                   "GGTATTTTAATT" "GGTATTTTAATTTATAGT"))])
+      (let ([table (all-counts (string-length seq) dna)])
+        (if (hash-has-key? table seq)
+            (deref (hash-ref table seq))
+            0)))
+  : (List Int) 
+  -> (list 5861 1776 176 0 0))
+  #;(write-one-freq (all-counts (string-length seq) dna)
+                  seq)
diff --git a/tapl/tests/run-all-mlish-tests.rkt b/tapl/tests/run-all-mlish-tests.rkt
index e1f0dee..48fb42f 100644
--- a/tapl/tests/run-all-mlish-tests.rkt
+++ b/tapl/tests/run-all-mlish-tests.rkt
@@ -7,3 +7,7 @@
 (require "mlish/ary.mlish")
 (require "mlish/fannkuch.mlish")
 (require "mlish/fasta.mlish")
+(require "mlish/fibo.mlish")
+(require "mlish/hash.mlish")
+;(require "mlish/heapsort.mlish")
+(require "mlish/knuc.mlish")