diff --git a/examples/lazyseqs.dst b/examples/lazyseqs.dst
index c3d8695f..b65d1284 100644
--- a/examples/lazyseqs.dst
+++ b/examples/lazyseqs.dst
@@ -136,8 +136,7 @@ body once, and then memoizes the result."
 # data structures as their values are references to this
 # data structures. Same is true for iterators
 
-(defn filter2 [pred coll]
-  (tail (iter2lazy (filter pred coll))))
+(defn filter2 [pred coll] (iter2lazy (filter pred coll)))
 
 # be careful with the filter function. First element in (filter pos? arr) is nil
 # last element is false
diff --git a/examples/maxtriangle.dst b/examples/maxtriangle.dst
new file mode 100644
index 00000000..ee895f5e
--- /dev/null
+++ b/examples/maxtriangle.dst
@@ -0,0 +1,42 @@
+# Find the maximum path from the top (root)
+# of the triangle to the leaves of the triangle.
+  
+(defn vmap2 [f m1 m2] 
+ (def len (length m1))
+ (def arr @[])
+ (for [i 0 len] (array-push arr (f (get m1 i) (get m2 i))))
+ arr)
+
+(defn reduce [s f c]
+ (var res s)
+ (for [i 0 (length c)]
+  (:= res (f res (get c i))))
+ res)
+
+(defn max1 [l r] (if (< l r) r l))
+    
+(defn myfold [xs ys]
+ (def xs1 (tuple-prepend xs 0))
+ (def xs2 (tuple-append xs 0))
+ (def m1 (vmap2 + xs1 ys))
+ (def m2 (vmap2 + xs2 ys))
+ (vmap2 max1 m1 m2))
+
+(defn max [a]
+ (var m (get a 0))
+ (for [i 0 (length a)]
+  (if (< m (get a i))
+   (:= m (get a i))))
+ m)
+
+(defn maxpath [t]
+ (max (reduce () myfold t)))
+
+(def triangle @[
+ @[3]
+ @[7 10]
+ @[4 3 7]
+ @[8 9 1 3]
+])
+
+(print (maxpath triangle))
diff --git a/examples/utils.dst b/examples/utils.dst
new file mode 100644
index 00000000..8f252e33
--- /dev/null
+++ b/examples/utils.dst
@@ -0,0 +1,22 @@
+
+(defn put-in [coll keys val]
+  (defn assoc [the-coll n]
+    (if-let [current-key (get keys n)
+             current-val (get the-coll current-key)]
+          (put the-coll current-key (assoc current-val (inc n)))
+      val))
+  (assoc coll 0))
+
+
+(defn update-in [coll keys an-fn]
+  (def new-keys (array-slice  coll 0 -2) )
+  (def last-key (get (array-slice  coll -1 -2) 0))
+  (defn assoc [the-coll n]
+    (if-let [current-key (get keys n)
+             current-val (get the-coll current-key)]
+      (put the-coll current-key (assoc current-val (inc n)))
+      ( update  the-coll last-key an-fn )))
+  (assoc coll  new-keys   0))
+
+
+;; (defn update-in-test [ ] (update-in @{:a "x" :b {:y {"pipa" 3}}} [:b :y "pipa"] type))
diff --git a/src/compiler/boot.dst b/src/compiler/boot.dst
index 2727b7b0..4635c667 100644
--- a/src/compiler/boot.dst
+++ b/src/compiler/boot.dst
@@ -1,13 +1,13 @@
 # Bootstrap the dst environment
 # Copyright 2018 (C) Calvin Rose
 
-(var *env* 
+(var *env*
  "The current environment."
  _env)
 
 (def defn :macro
  "Define a function"
-  (fn [name & more] 
+  (fn [name & more]
    (def fstart (fn recur [i]
     (def ith (ast-unwrap1 (get more i)))
     (def t (type ith))
@@ -24,8 +24,8 @@
  (do
   (def defn* (get (get _env 'defn) :value))
   (fn [name & more] 
-   (def args (array-concat @[] name :macro more))
-   (apply1 defn* args))))
+   (apply1 defn* (array-concat
+    @[name :macro] more)))))
 
 (defmacro defmacro-
  "Define a private macro that will not be exported."
@@ -86,7 +86,7 @@
 
 (defmacro when
  "Evaluates the body when the condition is true. Otherwise returns nil."
- [cond & body] 
+ [cond & body]
  (tuple 'if cond (tuple-prepend body 'do)))
 
 (defmacro cond
@@ -140,21 +140,21 @@ If no match is found, returns nil"
    (tuple 'def sym dispatch)
    (aux 0)))
 
-(defmacro and [& forms] 
+(defmacro and [& forms]
  (def len (length forms))
  (if (= len 0) true ((fn aux [i]
   (cond
    (>= (inc i) len) (get forms i)
    (tuple 'if (get forms i) (aux (inc i)) false))) 0)))
 
-(defmacro or [& forms] 
+(defmacro or [& forms]
  (def len (length forms))
  (if (= len 0) false ((fn aux [i]
   (cond
    (>= (inc i) len) (get forms i)
    (tuple 'if (get forms i) true (aux (inc i))))) 0)))
 
-(defn identity 
+(defn identity
  "A function that returns its first argument."
 [x] x)
 
@@ -167,7 +167,7 @@ If no match is found, returns nil"
       :next (fn []
         (def ret (get x i))
         (:= i (+ i 1))
-        ret) 
+        ret)
     })
   (def iters {
     :array array-iter
@@ -184,20 +184,20 @@ If no match is found, returns nil"
     :next (fn []
       (def ret i)
       (:= i (+ i 1))
-      ret) 
+      ret)
   })
 
 (defn range [top] (range2 0 top))
 
-(defn doiter [itr] 
+(defn doiter [itr]
  (def {:more more :next next} (iter itr))
  (while (more) (next)))
 
-(defn foreach [itr f] 
+(defn foreach [itr f]
  (def {:more more :next next} (iter itr))
  (while (more) (f (next))))
 
-(defn iter2array [itr] 
+(defn iter2array [itr]
  (def {:more more :next next} (iter itr))
  (def a @[])
  (while (more) (array-push a (next)))
@@ -238,7 +238,7 @@ If no match is found, returns nil"
   (var i 0)
   (var accum @['do])
   (while (< i len)
-   (array-push accum (tuple 'def 
+   (array-push accum (tuple 'def
                      (get head i)
                      (get head (+ 1 i))))
    (:= i (+ i 2)))
@@ -368,26 +368,30 @@ If no match is found, returns nil"
   (tuple 'when (tuple not condition) exp-1))
 
 (defmacro if-let
-"Takes the first one or two forms in a vector and if true binds
+"Takes the first one or two forms in a vector and if both are  true binds
  all the forms with let and evaluates the first expression else
  evaluates the second"
   [bindings then else]
-  (def head (ast-unwrap1 bindings))
-  (tuple 'let head
-         (tuple 'if (and (get head 1) (if (get head 2) (get head 3) true))
+  (tuple 'let bindings
+         (tuple 'if (tuple 'and (tuple 'get bindings 1)
+                           (tuple 'if
+                                  (tuple '> (tuple 'length bindings) 2)
+                                  (tuple 'get bindings 3) 'true))
               then
               else)))
 
 (defmacro when-let
 "Takes the first one or two forms in vector and if true binds
- all the forms  with let and evaluates body"
+ all the forms  with let and evaluates the body"
   [bindings & body]
-  (def head (ast-unwrap1 bindings))
-  (tuple 'let head
+  (tuple 'let bindings
       (tuple
         'when
-        (and (get head 1) (if (get head 2) (get head 3) true))
-        (apply1 tuple (array-concat @['do] (ast-unwrap1 body))))))
+        (tuple 'and (tuple 'get bindings 1)
+                           (tuple 'if
+                                  (tuple '> (tuple 'length bindings) 2)
+                                  (tuple 'get bindings 3) 'true))
+        (apply1 tuple (array-concat @['do] body)))))
 
 (defn comp
 "Takes multiple functions and returns a function that is the composition
@@ -404,21 +408,21 @@ If no match is found, returns nil"
       (tuple-slice functions 5 -1)))))
 
 (defn zipcoll
-"Creates an table or tuple from two arrays/tuples. Result is table if no
-third argument is given"
+"Creates an table or tuple from two arrays/tuples. If a third argument of
+ :struct is givent resault is struct else is table."
   [coll-1 coll-2 the-type]
   (var zipping-table @{})
   (def {:more more1 :next next1} (iter coll-1))
   (def {:more more2 :next next2} (iter coll-2))
   (while (and (more1) (more2))
     (put zipping-table (next1) (next2)))
-  (if (= :struct the-type)
+  (if (struct? the-type)
     (table-to-struct zipping-table)
     zipping-table))
 
 (defn update
-"Accepts a key argument and passes its associated value to a function.
- The key, then is associated to that value"
+"Accepts a key argument and passes its' associated value to a function.
+ The key then, is associated to the function's return value"
   [coll a-key a-function & args]
   (def old-value (get coll a-key))
   (put coll a-key (apply a-function old-value args)))
@@ -477,8 +481,8 @@ third argument is given"
    :struct (fn [pp seen buf x] (pp-dict pp seen buf x "{" "}"))
   })
 
-  (defn- default_printer [pp seen buf x] 
-   (buffer-push-string buf (describe x)) 
+  (defn- default_printer [pp seen buf x]
+   (buffer-push-string buf (describe x))
    buf)
 
   (defn- pp1 [seen buf x]
@@ -498,7 +502,7 @@ third argument is given"
  "Expand macros in a form, but do not recursively expand macros."
  [x]
 
- (defn doarray [a] 
+ (defn doarray [a]
   (def len (length a))
   (def newa @[])
   (for [i 0 len] 
@@ -536,7 +540,7 @@ third argument is given"
       'quote identity
       'var expandlast
       'while expandall
-   }) 
+   })
 
  (defn dotup [t]
   (def h (get t 0))
@@ -589,7 +593,7 @@ third argument is given"
  (put newenv '_env @{:value newenv :private true})
  newenv)
 
-(def run-context 
+(def run-context
 "Run a context. This evaluates expressions of dst in an environment,
 and is encapsulates the parsing, compilation, and evaluation of dst.
 env is the environment to evaluate the code in, chunks is a function
@@ -597,7 +601,7 @@ that returns strings or buffers of source code (from a repl, file,
 network connection, etc. onvalue and onerr are callbacks that are
 invoked when a result is returned and when an error is produced,
 respectively.
- 
+
 This function can be used to implemement a repl very easily, simply
 pass a function that reads line from stdin to chunks, and print to
 onvalue."
@@ -610,7 +614,7 @@ onvalue."
    (var len 1)
    (while (< 0 len)
       (buffer-clear buf)
-      (chunks buf) 
+      (chunks buf)
       (:= len (length buf))
       (for [i 0 len]
         (yield (get buf i))))
@@ -678,7 +682,7 @@ onvalue."
     } (get st i))
    (file-write stdout "  in")
    (when c (file-write stdout " cfunction"))
-   (when name (file-write stdout (string " " name))) 
+   (when name (file-write stdout (string " " name)))
    (when func (file-write stdout (string " " func)))
    (when pc (file-write stdout (string " (pc=" pc ")")))
    (when tail (file-write stdout " (tailcall)"))
@@ -712,7 +716,7 @@ onvalue."
    (put env (symbol (if prefix prefix "") k) v)))))
 
 (defmacro import [path & args]
- (apply tuple import* '_env path args)) 
+ (apply tuple import* '_env path args))
 
 (defn repl [getchunk]
  (def newenv (make-env))
diff --git a/src/compiler/specials.c b/src/compiler/specials.c
index 86209adc..17d6f21b 100644
--- a/src/compiler/specials.c
+++ b/src/compiler/specials.c
@@ -45,7 +45,7 @@ DstSlot dstc_astquote(DstFopts opts, DstAst *ast, int32_t argn, const Dst *argv)
 }
 
 static void destructure(DstCompiler *c, Dst left, DstSlot right,
-        void (*leaf)(DstCompiler *c, 
+        void (*leaf)(DstCompiler *c,
             DstAst *ast,
             const uint8_t *sym,
             DstSlot s,
@@ -72,7 +72,7 @@ static void destructure(DstCompiler *c, Dst left, DstSlot right,
                     localright = dstc_preread(c, ast, 0xFF, 1, right);
                     localsub = dstc_lslotn(c, 0xFF, 3);
                     if (i < 0x100) {
-                        dstc_emit(c, ast, 
+                        dstc_emit(c, ast,
                                 (i << 24) |
                                 (localright << 16) |
                                 (localsub << 8) |
@@ -80,7 +80,7 @@ static void destructure(DstCompiler *c, Dst left, DstSlot right,
                     } else {
                         DstSlot islot = dstc_cslot(dst_wrap_integer(i));
                         int32_t locali = dstc_preread(c, ast, 0xFF, 2, islot);
-                        dstc_emit(c, ast, 
+                        dstc_emit(c, ast,
                                 (locali << 24) |
                                 (localright << 16) |
                                 (localsub << 8) |
@@ -111,7 +111,7 @@ static void destructure(DstCompiler *c, Dst left, DstSlot right,
                     localright = dstc_preread(c, ast, 0xFF, 1, right);
                     localsub = dstc_lslotn(c, 0xFF, 3);
                     int32_t localk = dstc_preread(c, ast, 0xFF, 2, kslot);
-                    dstc_emit(c, ast, 
+                    dstc_emit(c, ast,
                             (localk << 24) |
                             (localright << 16) |
                             (localsub << 8) |
@@ -211,7 +211,7 @@ static DstSlot namelocal(DstCompiler *c, DstAst *ast, Dst head, int32_t flags, D
         ret = localslot;
     }
     ret.flags |= flags;
-    dstc_nameslot(c, dst_unwrap_symbol(head), ret); 
+    dstc_nameslot(c, dst_unwrap_symbol(head), ret);
     return ret;
 }
 
@@ -276,7 +276,7 @@ static void defleaf(
         tableindex = dstc_preread(c, ast, 0xFF, 1, tabslot);
         valsymindex = dstc_preread(c, ast, 0xFF, 2, valsym);
         valueindex = dstc_preread(c, ast, 0xFF, 3, s);
-        dstc_emit(c, ast, 
+        dstc_emit(c, ast,
                 (valueindex << 24) |
                 (valsymindex << 16) |
                 (tableindex << 8) |
@@ -352,7 +352,7 @@ DstSlot dstc_if(DstFopts opts, DstAst *ast, int32_t argn, const Dst *argv) {
     }
 
     /* Set target for compilation */
-    target = (drop || tail) 
+    target = (drop || tail)
         ? dstc_cslot(dst_wrap_nil())
         : dstc_gettarget(opts);
 
@@ -366,7 +366,7 @@ DstSlot dstc_if(DstFopts opts, DstAst *ast, int32_t argn, const Dst *argv) {
     /* Condition left body */
     dstc_scope(c, 0);
     left = dstc_value(bodyopts, truebody);
-    if (!drop && !tail) dstc_copy(c, ast, target, left); 
+    if (!drop && !tail) dstc_copy(c, ast, target, left);
     dstc_popscope(c);
 
     /* Compile jump to done */
@@ -377,7 +377,7 @@ DstSlot dstc_if(DstFopts opts, DstAst *ast, int32_t argn, const Dst *argv) {
     labelr = dst_v_count(c->buffer);
     dstc_scope(c, 0);
     right = dstc_value(bodyopts, falsebody);
-    if (!drop && !tail) dstc_copy(c, ast, target, right); 
+    if (!drop && !tail) dstc_copy(c, ast, target, right);
     dstc_popscope(c);
 
     /* Write jumps - only add jump lengths if jump actually emitted */
@@ -584,7 +584,7 @@ DstSlot dstc_fn(DstFopts opts, DstAst *ast, int32_t argn, const Dst *argv) {
         dstc_freeslot(c, s);
         if (dstc_iserr(&opts)) return dstc_cslot(dst_wrap_nil());
     }
-    
+
     /* Build function */
     def = dstc_pop_funcdef(c);
     def->arity = arity;
@@ -603,9 +603,9 @@ DstSlot dstc_fn(DstFopts opts, DstAst *ast, int32_t argn, const Dst *argv) {
             (defindex << 16) |
             (localslot << 8) |
             DOP_CLOSURE);
-    
+
     if (ret.index != localslot) {
-        dstc_emit(c, ast, 
+        dstc_emit(c, ast,
                 (ret.index << 16) |
                 (localslot << 8) |
                 DOP_MOVE_FAR);
@@ -614,7 +614,7 @@ DstSlot dstc_fn(DstFopts opts, DstAst *ast, int32_t argn, const Dst *argv) {
     return ret;
 }
 
-/* Keep in lexographic order */
+/* Keep in lexicographic order */
 static const DstSpecial dstc_specials[] = {
     {":=", dstc_varset},
     {"ast-quote", dstc_astquote},
diff --git a/src/core/tuple.c b/src/core/tuple.c
index 358a8363..b851f639 100644
--- a/src/core/tuple.c
+++ b/src/core/tuple.c
@@ -127,25 +127,25 @@ static int cfun_slice(DstArgs args) {
 
 static int cfun_prepend(DstArgs args) {
     const Dst *t;
+    int32_t len;
     Dst *n;
     if (args.n != 2) return dst_throw(args, "expected 2 arguments");
-    if (!dst_checktype(args.v[0], DST_TUPLE)) return dst_throw(args, "expected tuple");
-    t = dst_unwrap_tuple(args.v[0]);
-    n = dst_tuple_begin(dst_tuple_length(t) + 1);
-    memcpy(n + 1, t, sizeof(Dst) * dst_tuple_length(t));
+    if (!dst_seq_view(args.v[0], &t, &len)) return dst_throw(args, "expected tuple/array");
+    n = dst_tuple_begin(len + 1);
+    memcpy(n + 1, t, sizeof(Dst) * len);
     n[0] = args.v[1];
     return dst_return(args, dst_wrap_tuple(dst_tuple_end(n)));
 }
 
 static int cfun_append(DstArgs args) {
     const Dst *t;
+    int32_t len;
     Dst *n;
     if (args.n != 2) return dst_throw(args, "expected 2 arguments");
-    if (!dst_checktype(args.v[0], DST_TUPLE)) return dst_throw(args, "expected tuple");
-    t = dst_unwrap_tuple(args.v[0]);
-    n = dst_tuple_begin(dst_tuple_length(t) + 1);
-    memcpy(n, t, sizeof(Dst) * dst_tuple_length(t));
-    n[dst_tuple_length(t)] = args.v[1];
+    if (!dst_seq_view(args.v[0], &t, &len)) return dst_throw(args, "expected tuple/array");
+    n = dst_tuple_begin(len + 1);
+    memcpy(n, t, sizeof(Dst) * len);
+    n[len] = args.v[1];
     return dst_return(args, dst_wrap_tuple(dst_tuple_end(n)));
 }