Erlang 打印出递归的每个步骤

我正在使用Erlang shell测试该语言，我用两种方法编写了一个求和函数：一种是更经典的递归求和，另一种是使用尾部递归。第二个是线性的，第一个随着输入的大小而增长

如何查看递归的每个步骤？我希望它打印出每一步的当前值，这样我就可以更好地了解发生了什么

以下是我的两项职能：

正常递归：

sum([]) -> 0;
sum([H|T]) -> H + sum(T).

尾部递归：

tail_sum(List) -> tail_sum(List, 0).
tail_sum([], Sum) -> Sum;
tail_sum([H|T], Sum) -> tail_sum(T, H+Sum).

---

Erlang中的

dbg

模块为此提供了一个有用的特性：跟踪。假设您的代码在模块

a

中，您将如何跟踪这些函数：

设置：

1> c(a). % load a.erl
{ok,a}
2> dbg:tracer(). % start the default trace message receiver
{ok,<0.71.0>}
3> dbg:p(all, c). % setup call tracing on all processes
{ok,[{matched,nonode@nohost,34}]}
4> dbg:tpl(a, '_', '_', []). % trace all functions in a
{ok,[{matched,nonode@nohost,5}]}

---

Erlang中的

dbg

模块为此提供了一个有用的特性：跟踪。假设您的代码在模块

a

中，您将如何跟踪这些函数：

设置：

1> c(a). % load a.erl
{ok,a}
2> dbg:tracer(). % start the default trace message receiver
{ok,<0.71.0>}
3> dbg:p(all, c). % setup call tracing on all processes
{ok,[{matched,nonode@nohost,34}]}
4> dbg:tpl(a, '_', '_', []). % trace all functions in a
{ok,[{matched,nonode@nohost,5}]}

---

我刚刚编辑了我的答案，包括

返回跟踪

。这对你来说应该更有用。跟踪是我最喜欢的ErlangVM特性之一！我刚刚编辑了我的答案，包括

返回跟踪

。这对你来说应该更有用。跟踪是我最喜欢的ErlangVM特性之一！

7> dbg:tpl(a, '_', '_', [{'_',[],[{return_trace}]}]).
(<0.64.0>) call a:module_info()
{ok,[{matched,nonode@nohost,5},{saved,1}]}
8> a:sum(lists:seq(1, 10)).
(<0.64.0>) call a:sum([1,2,3,4,5,6,7,8,9,10])
(<0.64.0>) call a:sum([2,3,4,5,6,7,8,9,10])
(<0.64.0>) call a:sum([3,4,5,6,7,8,9,10])
(<0.64.0>) call a:sum([4,5,6,7,8,9,10])
(<0.64.0>) call a:sum([5,6,7,8,9,10])
(<0.64.0>) call a:sum([6,7,8,9,10])
(<0.64.0>) call a:sum([7,8,9,10])
(<0.64.0>) call a:sum("\b\t\n")
(<0.64.0>) call a:sum("\t\n")
(<0.64.0>) call a:sum("\n")
(<0.64.0>) call a:sum([])
(<0.64.0>) returned from a:sum/1 -> 0
(<0.64.0>) returned from a:sum/1 -> 10
(<0.64.0>) returned from a:sum/1 -> 19
(<0.64.0>) returned from a:sum/1 -> 27
(<0.64.0>) returned from a:sum/1 -> 34
(<0.64.0>) returned from a:sum/1 -> 40
(<0.64.0>) returned from a:sum/1 -> 45
(<0.64.0>) returned from a:sum/1 -> 49
(<0.64.0>) returned from a:sum/1 -> 52
(<0.64.0>) returned from a:sum/1 -> 54
(<0.64.0>) returned from a:sum/1 -> 55
55
9> a:tail_sum(lists:seq(1, 10)).
(<0.64.0>) call a:tail_sum([1,2,3,4,5,6,7,8,9,10])
(<0.64.0>) call a:tail_sum([1,2,3,4,5,6,7,8,9,10],0)
(<0.64.0>) call a:tail_sum([2,3,4,5,6,7,8,9,10],1)
(<0.64.0>) call a:tail_sum([3,4,5,6,7,8,9,10],3)
(<0.64.0>) call a:tail_sum([4,5,6,7,8,9,10],6)
(<0.64.0>) call a:tail_sum([5,6,7,8,9,10],10)
(<0.64.0>) call a:tail_sum([6,7,8,9,10],15)
(<0.64.0>) call a:tail_sum([7,8,9,10],21)
(<0.64.0>) call a:tail_sum("\b\t\n",28)
(<0.64.0>) call a:tail_sum("\t\n",36)
(<0.64.0>) call a:tail_sum("\n",45)
(<0.64.0>) call a:tail_sum([],55)
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/2 -> 55
(<0.64.0>) returned from a:tail_sum/1 -> 55
55