SICP exercise solution in Groovy (2)

Exercise 1.12
Write a procedure that computes elements of Pascal's triangle by means of a recursive
process.

def elem(n, m) {
    if (m == 1 || m == n) return 1
    else if (m < 1 || m > n) return 0
    else return elem(n-1, m-1) + elem(n-1, m);
}

def line(n) {
    def line_iter;
    line_iter = { total, id ->
        if (id > total) return [];
        else return ([elem(total, id)] + line_iter(total, id+1));
    }
    return line_iter(n, 1);
}

def pascalTriangle(n) {
    def impl = { id ->
        if (id == 0) return "";
        else return "${pascalTriangle(id - 1)}\n${line(id)}"
    }
    return impl(n);
}

println pascalTriangle(7);

------------------result----------------

[1]
[1, 1]
[1, 2, 1]
[1, 3, 3, 1]
[1, 4, 6, 4, 1]
[1, 5, 10, 10, 5, 1]
[1, 6, 15, 20, 15, 6, 1]


上面那一版pascalTriangle()写得不好，定义了一个多余的闭包。下面是修改版：

def elem(n, m) {
    if (m == 1 || m == n) return 1
    else if (m < 1 || m > n) return 0
    else return elem(n-1, m-1) + elem(n-1, m);
}

def line(n) {
    def line_iter;
    line_iter = { total, id ->
        if (id > total) return [];
        else return ([elem(total, id)] + line_iter(total, id+1));
    }
    return line_iter(n, 1);
}

def pascalTriangle(n) {
    if (n == 0) return "";
    else return "${pascalTriangle(n - 1)}\n${line(n)}"
}

println pascalTriangle(7);