因为Erlang变量是不可变的，根本不能改变。lists:append返回一个新的列表，您可以将其丢弃。

正如@Alexey Romanov正确指出的那样，你没有使用lists:append/2的结果。
这就是我如何修复你的代码...

-module(pmap). 
-export([start/0,test/2]). 

test(Lst1,0) ->
    {ok, [Temp]} = io:fread( "Input the edge weight  ", "~d" ),
    Lst2 = lists:append([Lst1,[Temp]]),
    io:fwrite("~w~n",[Lst2]),
    Lst2;
test(Lst1,V) ->
    {ok, [Temp]} = io:fread( "Input the edge weight  ", "~d" ),
    Lst2 = lists:append([Lst1,[Temp]]),
    test(Lst2, V-1).

start() -> 
   {ok, [V]} = io:fread( "Input the number of vertices your graph has  ", "~d" ),
   Lst1 = [],
   test(Lst1,V).

但实际上，一个更 * 惯用 * 的代码来实现同样的结果将是...

-module(pmap). 
-export([start/0,test/2]). 

test(Lst1,0) ->
    {ok, [Temp]} = io:fread( "Input the edge weight  ", "~d" ),
    Lst2 = lists:reverse([Temp|Lst1]),
    io:fwrite("~w~n",[Lst2]),
    Lst2;
test(Lst1,V) ->
    {ok, [Temp]} = io:fread( "Input the edge weight  ", "~d" ),
    test([Temp | Lst1], V-1).

start() -> 
   {ok, [V]} = io:fread( "Input the number of vertices your graph has  ", "~d" ),
   Lst1 = [],
   test(Lst1,V).