Feature: Data stream flow control

[AjaniBilby]

This language will avoid the archaic for loop style, as the more commonly used for .. of/in pattern used my other languages is the same behaviour as a map however with different syntactical sugar.
However in most languages map/filter produced new containers after each operation which is a waste of allocations, instead these operations should be streamlined into a single execution unit producing a final result, rather than multiple intermittent results.

I.e. The bellow snippet should only produce one final array, and ideally in this case since arr is being consumed, and there is a 1:1 relationship between inputs and outputs, the container which held the input values should be reused for the output which would result in zero allocations or data shifting

arr.map(x => x*2).map(x => x-3).map(x => x % 4)

Initially there were going to be six operators creating symmetrical control:

• Unfold: 1:m
• Expand: n:m where n<=m
• Map: 1:1
• Filter: n:m where n>=m
• Reduce: n:m where n>=m
• Fold: n:1

However expand is simply a unfold nested inside of a map, and there is little increase in syntactic complexity simplifying the operation into a single operator.
However removing filter and insead relying on reduce would rely on a runtime either type between the streamed value and void, which means values would mean the values would need to be packed into a struct then read back out to be determined if they need to be dropped. So breaking filter into its own operation can save on extra type syntax and compilation complexities and possible runtime side affects on lower levels of optimisation.
Reduce can also be eliminated as it is simply a reduce which has been designed to only yield once.

Unfold:

let val = 64;
@val unfold (x) => {
  if (x > 2) {
    x = x/2;
    yield 2:
  } else {
    finish;
  }
} map (x) => {
  printf("Divided by %i", x);
}

Filter:

&arr filter (x) => {
  ret x % 2;
} map (x) => {
  printf("Even numbers %i", x);
}

Reduce:

// Squash the array so each element sums with it's neighbour and length /= 2
let buf = Vec#[int].new();
concat { arr, buff } reduce (x => {
  if (buf->length() > 0) {
    yield buf->pop() + x;
  } else {
    buf.push(x);
  }
  // reached end of block, load next elm and repeat
} map (x) => { printf("%i", x) }

Concat
When allows multiple sources of the same data type, when one source stops starting feeding from the next source

[AjaniBilby]

This fulfills issues #9 #8 #7 #6 and thus makes them irrelevant