I'm studying lua AI, and I have problems with the following

[pku_ai_study]

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local keeps = wesnoth.get_locations 
            {
                terrain = 'K*,K*^*,*^K*', -- Keeps
                x = '1-'..width,
                y = '1-'..height,
                { "not", { {"filter", {}} }}, -- That have no unit
                { "not", { radius = 6, {"filter", { canrecruit = 'yes',
                    { "filter_side", { { "enemy_of", {side = wesnoth.current.side} } } }
                }} }}, -- That are not too close to an enemy leader
                { "not", {
                    x = leader.x, y = leader.y, terrain = 'K*,K*^*,*^K*',
                    radius = 3,
                    { "filter_radius", { terrain = 'C*,K*,C*^*,K*^*,*^K*,*^C*' } }
                }}, -- That are not close and connected to a keep the leader is on
                { "filter_adjacent_location", {
                    terrain = 'C*,K*,C*^*,K*^*,*^K*,*^C*'
                }} -- That are not one-hex keeps
            }

I am just wondering what the params of the function get_locations mean, and how can I define those params.

[mattsc]

wesnoth.get_locations() takes a Standard Location Filter (SLF) as defined on the wiki here. So that will tell you what the parameters mean.

As for the syntax, a WML tag such as

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[tag]
    key1=value1
    key2=value2
[/tag]

is coded in Lua like this

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{ "tag", { key1 = value1, key2 = value2 } }

Formatted somewhat differently (possibly easier to decipher), since line breaks don't matter in Lua, you could also write it like this

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{ "tag", 
    {
        key1 = value1,
        key2 = value2
    }
}

Note that the "", the commas and all the brackets are important and cannot be omitted.

Thus, the beginning of your example is the Lua version of the following WML code (for simplicity for this example, I assumed that the Lua variable 'width' equals 20, and 'height' equals 15):

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    terrain = 'K*,K*^*,*^K*'    # Keeps
    x = 1-20
    y = 1-15
    [not]    # That have no unit
        [filter]
        [/filter]
    [/not]
    [not]    # That are not too close to an enemy leader
        radius = 6
        [filter]
            canrecruit = yes
            [filter_side]
                [enemy_of]
                    side = $side_number
                [/enemy_of]
            [/filter_side]
       [/filter]
    [/not]
    ...

Hope that helps and it's always great having somebody trying to work on Wesnoth AIs!