diff --git a/lib.nas b/lib.nas
index 696f3b1..aae4964 100644
--- a/lib.nas
+++ b/lib.nas
@@ -372,7 +372,9 @@ var math=
     ln:    func(x)  {return __builtin_ln(x);     },
     sqrt:  func(x)  {return __builtin_sqrt(x);   },
     atan2: func(x,y){return __builtin_atan2(x,y);},
-    isnan: func(x)  {return __builtin_isnan(x);  }
+    isnan: func(x)  {return __builtin_isnan(x);  },
+    max:   func(x,y){return x>y?x:y;             },
+    min:   func(x,y){return x<y?x:y;             }
 };
 
 var unix=
diff --git a/stl/lib.nas b/stl/lib.nas
index 696f3b1..aae4964 100644
--- a/stl/lib.nas
+++ b/stl/lib.nas
@@ -372,7 +372,9 @@ var math=
     ln:    func(x)  {return __builtin_ln(x);     },
     sqrt:  func(x)  {return __builtin_sqrt(x);   },
     atan2: func(x,y){return __builtin_atan2(x,y);},
-    isnan: func(x)  {return __builtin_isnan(x);  }
+    isnan: func(x)  {return __builtin_isnan(x);  },
+    max:   func(x,y){return x>y?x:y;             },
+    min:   func(x,y){return x<y?x:y;             }
 };
 
 var unix=
diff --git a/test/diff.nas b/test/diff.nas
new file mode 100644
index 0000000..f13ae3f
--- /dev/null
+++ b/test/diff.nas
@@ -0,0 +1,137 @@
+var myers=func(src,dst,show_table=0){
+    (src,dst)=(split("\n",src),split("\n",dst));
+    append(src,"");
+    append(dst,"");
+    var (src_len,dst_len)=(size(src),size(dst));
+
+    var mat=[];
+    setsize(mat,dst_len);
+    forindex(var i;mat){
+        var tmp=[];
+        setsize(tmp,src_len);
+        mat[i]=tmp;
+        forindex(var j;tmp)
+            tmp[j]=0;
+    }
+    var visited=[];
+    setsize(visited,dst_len);
+    forindex(var i;visited){
+        var tmp=[];
+        setsize(tmp,src_len);
+        visited[i]=tmp;
+        forindex(var j;tmp)
+            tmp[j]=0;
+    }
+
+    forindex(var y;dst)
+        forindex(var x;src)
+            mat[y][x]=(src[x]==dst[y]);
+
+    if(show_table){
+        var curve=[
+            ["+---",
+            "|   "],
+            [
+            "+---",
+            "| \\ "]
+        ];
+        var s="";
+        forindex(var y;dst){
+            forindex(var t;curve[0]){
+                forindex(var x;src){
+                    s~=curve[mat[y][x]][t];
+                }
+                s~=["+","|"][t]~"\n";
+            }
+        }
+        forindex(var i;src)
+            s~="+---";
+        print(s~"+\n");
+    }
+
+    var total=[];
+    var path=[];
+    var vec=[[0,0,-1]];
+    visited[0][0]=1;
+    while(size(vec)){
+        append(total,vec);
+        var tmp=[];
+        forindex(var i;vec){
+            var elem=vec[i];
+            var (x,y)=(elem[1],elem[0]);
+
+            # find solution
+            if(x==src_len-1 and y==dst_len-1){
+                append(path,vec[i]);
+                for(var (prev,iter)=(elem[2],size(total)-1);iter>0;iter-=1){
+                    var t=total[iter-1][prev];
+                    append(path,t);
+                    prev=t[2];
+                }
+
+                if(show_table){
+                    for(var t=size(path)-1;t>=0;t-=1)
+                        print("("~path[t][1]~","~path[t][0]~")",t==0?"":"->");
+                    println();
+                }
+
+                # reverse path
+                for(var t=0;t<size(path)/2;t+=1)
+                    (path[t],path[-1-t])=(path[-1-t],path[t]);
+                # print diff
+                for(var t=1;t<size(path);t+=1){
+                    var (prev_x,prev_y)=(path[t-1][1],path[t-1][0]);
+                    var (x,y)=(path[t][1],path[t][0]);
+                    var (sub_x,sub_y)=(x-prev_x,y-prev_y);
+                    if(sub_x==1 and sub_y==1){
+                        if(show_table)
+                            println("    ",src[prev_x]);
+                    }elsif(sub_x==1 and sub_y==0){
+                        println("\e[31m -  ",src[prev_x],"\e[0m");
+                    }elsif(sub_x==0 and sub_y==1){
+                        println("\e[32m +  ",dst[prev_y],"\e[0m");
+                    }
+                }
+                return;
+            }
+
+            # do bfs
+            if(mat[y][x]==1){
+                if(x+1<src_len and y+1<dst_len and visited[y+1][x+1]==0){
+                    append(tmp,[y+1,x+1,i]);
+                    visited[y+1][x+1]=1;
+                }
+            }
+            else{
+                if(x+1<src_len and visited[y][x+1]==0){
+                    append(tmp,[y,x+1,i]);
+                    visited[y][x+1]=1;
+                }
+                if(y+1<dst_len and visited[y+1][x]==0){
+                    append(tmp,[y+1,x,i]);
+                    visited[y+1][x]=1;
+                }
+            }
+        }
+        vec=tmp;
+    }
+}
+
+func(diff){
+    diff(
+        "var a=0;\nvar b=1;\nprint(\"hello \",a);\nvar c=2;\nc=[];\nvar d=3;\nvar l=list();\nvar q=queue();\n",
+        "var a=0;\nvar b=1;\nb=[];\nprintln(\"hello \",a);\nvar c=2;\nvar d=3;\nprintln(\"hello world!\");\nvar l=list();\nvar q=queue();\n",
+        1
+    );
+    print("\n");
+    diff(
+        "A\nB\nC\nA\nB\nB\nA\n",
+        "C\nB\nA\nB\nA\nC\n",
+        1
+    );
+    print("\n");
+    diff(
+        io.fin("test/bf.nas"),
+        io.fin("test/bfcolored.nas")
+    );
+}(myers);
\ No newline at end of file
diff --git a/test/md5compare.nas b/test/md5compare.nas
index b1d4208..41488a1 100644
--- a/test/md5compare.nas
+++ b/test/md5compare.nas
@@ -58,6 +58,7 @@ var filechecksum=func(){
         "./test/calc.nas         ",
         "./test/choice.nas       ",
         "./test/class.nas        ",
+        "./test/diff.nas         ",
         "./test/exception.nas    ",
         "./test/fib.nas          ",
         "./test/filesystem.nas   ",