diff --git a/src/SwapSort.jl b/src/SwapSort.jl
index afcb5e3..644d453 100644
--- a/src/SwapSort.jl
+++ b/src/SwapSort.jl
@@ -6,6 +6,7 @@ export swapsort, tuplesort
 
 include("consts.jl")
 include("utils.jl")
+include("core.jl")
 
 """
     swapsort(a...; lt=isless, by=identity)
diff --git a/src/core.jl b/src/core.jl
new file mode 100644
index 0000000..3573a77
--- /dev/null
+++ b/src/core.jl
@@ -0,0 +1,26 @@
+macro makesorter(expr)
+    path = string(eval(expr))
+    sorterdict = JSON.parsefile(path)
+    N = sorterdict["N"]
+    L = sorterdict["L"]
+    D = sorterdict["D"]
+    funname = "swapsort$(N)_$(L)_$(D)"
+    ret = Meta.parse("function $funname(;kw...) end")
+    for k in 0:N-1
+        push!(ret.args[1].args, localval(k))
+    end
+    functionbody = ret.args[2].args
+    for (a,b) in sorterdict["nw"]
+        push!(functionbody, compswap(a,b))
+    end
+    push!(functionbody, returnvals(N))
+    return ret
+end
+
+macro registersorter(expr)
+    (N,L,D) = eval(expr)
+    ret = Expr(:block)
+    push!(ret.args, Meta.parse("swapsort($(varstring(N)); kw...) = swapsort$(N)_$(L)_$(D)($(varstring(N)); kw...)"))
+    push!(ret.args, Meta.parse("tuplesort(I::Tuple{Vararg{Any, $N}}; kw...) = swapsort$(N)_$(L)_$(D)(I...; kw...)"))
+    esc(ret)
+end
\ No newline at end of file
diff --git a/src/utils.jl b/src/utils.jl
index 5ab2f41..0708481 100644
--- a/src/utils.jl
+++ b/src/utils.jl
@@ -5,10 +5,32 @@ The same as `Base.minmax`, but supports `lt` and `by` keywords which works as th
 """
 min_max(x, y; lt=isless, by=identity) = lt(by(x), by(y)) ? (x,y) : (y,x)
 
+"""
+    varstring(N)
+
+Returns the string of argument list "a0,a1,...,a(N-1)".
+"""
 varstring(N) = string("a0", [",a$k" for k in 1:N-1]...)
+
+"""
+    _filename(N,L,D)
+
+The file that contains the infomation of constructing `swapsortN_L_D`.
+"""
 _filename(N,L,D) = "Sort_$(N)_$(L)_$(D).json"
+
+"""
+    keywords()
+
+The expression `kw...` in a function definition.
+"""
 keywords() = Expr(:parameters, Expr(:(...), :kw))
 
+"""
+    returnvals(N)
+
+The expression `return a1, a2, ..., a(N-1)`.
+"""
 function returnvals(N)
     ret = Expr(:return, Expr(:tuple))
     for k in 0:N-1
@@ -16,32 +38,18 @@ function returnvals(N)
     end
     ret
 end
+
+"""
+    localval(i)
+
+The `i`-th variable name `ai`.
+"""
 localval(i) = Symbol("a$i")
-compswap(i,j) = Expr(:(=), Expr(:tuple, localval(i), localval(j)), Expr(:call, :min_max, keywords(), localval(i), localval(j)))
 
-macro makesorter(expr)
-    path = string(eval(expr))
-    sorterdict = JSON.parsefile(path)
-    N = sorterdict["N"]
-    L = sorterdict["L"]
-    D = sorterdict["D"]
-    funname = "swapsort$(N)_$(L)_$(D)"
-    ret = Meta.parse("function $funname(;kw...) end")
-    for k in 0:N-1
-        push!(ret.args[1].args, localval(k))
-    end
-    functionbody = ret.args[2].args
-    for (a,b) in sorterdict["nw"]
-        push!(functionbody, compswap(a,b))
-    end
-    push!(functionbody, returnvals(N))
-    return ret
-end
+"""
+    compswap(i,j)
+
+The expression `ai, aj = min_max(ai, aj; kw...)`
+"""
+compswap(i,j) = Expr(:(=), Expr(:tuple, localval(i), localval(j)), Expr(:call, :min_max, keywords(), localval(i), localval(j)))
 
-macro registersorter(expr)
-    (N,L,D) = eval(expr)
-    ret = Expr(:block)
-    push!(ret.args, Meta.parse("swapsort($(varstring(N)); kw...) = swapsort$(N)_$(L)_$(D)($(varstring(N)); kw...)"))
-    push!(ret.args, Meta.parse("tuplesort(I::Tuple{Vararg{Any, $N}}; kw...) = swapsort$(N)_$(L)_$(D)(I...; kw...)"))
-    esc(ret)
-end
\ No newline at end of file