11th_October_environment_blocks_functions

// new declaration in new block/scope means new frame in cse machine

// functions


// from chapter 1:
/*
function make_adder(x){
    return y => x + y;
}

const add_4 = make_adder(4);
add_4(5);
*/

// but in cse machine: no substitution model
// so how does add_4 know that x is 4

// new frame with the parameters when we use y => x + y;

// every function application extends the environment in which the 
// function was created

// the new frame contains bindings of parameters to arguments
// no new frame if function has no parameters
// function body block evaluated in this new environment

// for lambda expressions
// create a function object, represented as two circles
// one circle points to body (text)
// other circle to the environment in which the lambda expression was evaluated
// closures


// VERY IMPORTANT:
// a function remembers the environment in which it was created
// DONT FORGET^

const square = x => x * x;
square(5);


// evaluating a function application
// evaluate subexpressions in current environmet
// then (somethinggg)


// create a new frame that points to the environment of the function
// new frame - bind the parameters to the arguments
// parameters are variables so assignment allowed
// evaluate the body block in the new environment

/*
.
.
.
.
.
*/


// state and identity
// const a = pair(2,3);
// const b = a;
// a === b; returns true cause points to same pair 

// const a = pair(2,3);
// const b = pair(2,3);
// a === b; returns false cause now points to diff pair