Recursion + global/referenced/object/array variables

Posted on October 1, 2019

Tags: induction

recursion in non-pure language is confusing because some variables are assigned by reference, particularly arrays.
In recursion with global/referenced/object variables, the recursively spawned child process can manipulate the global/referenced/object variable of the parent process.

A visual python version is python recursion with global/referenced/object variables

In the example below the recursively spawned process manipulated the

//When fusing recursion with a global object
//the recursively spawned child can modify the parent's variable's state
//in this case the parent's tokens got modified
//tokens in many way acts like a global variable
function mktree(tokens){
    // let tokens = [...tokens1] //if you uncomment this recursion breaks because tokens is a pure array
    let partialSol = []
    let head = tokens.shift() //THIS pops off the tokens of the original parent process
    if(head == '('){
        while(tokens[0] != ')'){ 
            console.log(tokens)
            let IH = mktree(tokens)
            partialSol.push(IH)
        }
        return partialSol
        
    }else{
        // console.log(rest)
        return head
    }

}

//When fusing recursion with a global object
//the recursively spawned child can modify the parent's variable's state
//in this case the parent's tokens got modified
//tokens in many way acts like a global variable
function mktree(tokens){
    let tokens = [...tokens1] //emulate a pure tokens that has no reference to the parent tokens
    let partialSol = []
    let head = tokens.shift() //THIS pops off the tokens of the current process
    if(head == '('){
        while(tokens[0] != ')'){ //There will be an inifinite recursion here
            console.log(tokens)
            let IH = mktree(tokens)
            partialSol.push(IH)
        }
        return partialSol
        
    }else{
        // console.log(rest)
        return head
    }

}