Why does this recursion keep freezing/crashing?

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1 
function setup()
    local cp_tree1 = Coprime( 2, 1, 1, nil )
    cp_tree1:generateBranchesUntilDepth( 2 ) --works fine
   cp_tree1:generateBranchesUntilDepth( 3 ) -- freezes Codea
    
end


Coprime = class()

function Coprime:init(a,b, depth, p)
    print ("Coprime:init(depth="..depth..","..a..","..b..")" )
    self.m = a 
    self.n = b
    self.b1 = nil
    self.b2 = nil
    self.b3 = nil
    self.parent = p or nil
    self.branchDepth = depth or 0
end

function Coprime:calcBranch( )
    local s = self
    local m = s.m
    local n = s.n
    local d = s.branchDepth+1
    s.b1 = Coprime(2*m-n, m, d, s) 
    s.b2 = Coprime(2*m+n, m, d, s )
    s.b3 = Coprime(m+2*n, n, d, s )
    return s.b1, s.b2, s.b3
end

function Coprime:generateBranchesUntilDepth( n )
    local s = self
    --local m = s.m
    --local n = s.n
    print(n, "generateBranchesUntilDepth() for cp("..s.m..","..s.n..")" )
    --local d = s.branchDepth+1
    local b1 = nil
    local b2 = nil
    local b3 = nil
    
    b1, b2, b3 = s:calcBranch()
    while( b1.branchDepth < n ) do 
        b1:generateBranchesUntilDepth( n ) --why does this recursion crash?
    end
    --[[
    while( b2.branchDepth < n ) do
        b2:generateBranchesUntilDepth( n )
    end
    while( b3.branchDepth < n ) do 
        b3:generateBranchesUntilDepth( n )
    end
    ]]--
end
2

your while loop never updates b1.branchDepth so you have forever b1.branchDepth < n true.

3

look at how i modified your code to get out the infinite loop, with an nmax control variable. This helps to understand what is going wrong

function setup()
    local cp_tree1 = Coprime( 2, 1, 1, nil )
    cp_tree1:generateBranchesUntilDepth( 2 ) --works fine
    cp_tree1:generateBranchesUntilDepth( 3 ) -- freezes Codea

end


Coprime = class()
nmax = 0
function Coprime:init(a,b, depth, p)
    nmax = nmax + 1
    print (tostring(nmax).." Coprime:init(depth="..depth..","..a..","..b..")" )
    self.m = a 
    self.n = b
    self.b1 = nil
    self.b2 = nil
    self.b3 = nil
    self.parent = p or nil
    self.branchDepth = depth or 0
end

function Coprime:calcBranch( )
    local s = self
    local m = s.m
    local n = s.n
    local d = s.branchDepth+1
    s.b1 = Coprime(2*m-n, m, d, s) 
    s.b2 = Coprime(2*m+n, m, d, s )
    s.b3 = Coprime(m+2*n, n, d, s )
    return s.b1, s.b2, s.b3
end

function Coprime:generateBranchesUntilDepth( n )
    local s = self
    --local m = s.m
    --local n = s.n
    print(n, "generateBranchesUntilDepth() for cp("..s.m..","..s.n..")" )
    --local d = s.branchDepth+1
    local b1 = nil
    local b2 = nil
    local b3 = nil

    b1, b2, b3 = s:calcBranch()
    while( b1.branchDepth < n and nmax<20) do 
        b1:generateBranchesUntilDepth( n ) --why does this recursion crash?
    end
    --[[
    while( b2.branchDepth < n ) do
        b2:generateBranchesUntilDepth( n )
    end
    while( b3.branchDepth < n ) do 
        b3:generateBranchesUntilDepth( n )
    end
    ]]--
end
4

as soon as I switched the while() to an if(), it worked :slight_smile:

5

you’re welcome…