Erlang新手求助：从零定义列表操作函数——筛选大于指定整数的元素

Hey there! As someone who’s navigated the early days of Erlang, I totally get wanting to build these list operations from scratch without leaning on the standard library. Let’s start with the bigger/2 function you outlined, and break down how to make it work step by step.

Core Idea #

Erlang’s list processing revolves around recursion, so we’ll use that pattern here. We’ll handle the empty list as our base case, then recursively check each element to see if it belongs in the result.

Full Implementation #

Here’s the function code, written without any standard library helpers:

bigger([], _Threshold) -> [];
bigger([Head | Tail], Threshold) when Head > Threshold ->
    [Head | bigger(Tail, Threshold)];
bigger([_Head | Tail], Threshold) ->
    bigger(Tail, Threshold).

How it works: #

• Base case: If the input list is empty ([]), we return an empty list—there’s nothing to filter!
• Matching case 1: When the first element (Head) is strictly greater than the threshold, we add it to our result list, then recursively process the rest of the list (Tail).
• Matching case 2: If Head isn’t bigger than the threshold, we skip it and keep processing the tail of the list.

Examples & Test Cases #

Required Example #

1> bigger([1,2,3,4,5],3).
[4,5]

Additional Test Case 1: Mixed values with a mid-range threshold #

2> bigger([10,5,15,3,20],7).
[10,15,20]

Additional Test Case 2: Negative numbers and a negative threshold #

3> bigger([-2,0,-5,3,-1],-1).
[0,3]

Bonus Edge Case: Empty input list #

4> bigger([], 10).
[]

Bonus Edge Case: All elements smaller than the threshold #

5> bigger([1,2,3], 4).
[]

Next Steps #

If you share the requirements for the other three list functions you need, I can walk through those implementations too—just let me know what each one is supposed to do!

内容的提问来源于stack exchange，提问作者yvvy19