YAMA 0003 - For loop / loop

• Author(s): Bhathiya Perera
• Status : ✅

Problem

Yaksha programming language does not offer a for syntax sugar. This is annoying for someone coming from Python or other languages that has this feature. We have foreach builtin and while loop, which can be used at the moment. for can make certain things easy.

Use case 1 - for each element in array ✅

How it works now

items: Array[int] = get_it()

c: int = 0
length: int = len(items)

while c < length:
    if items[c] == 2:
        c += 1 
        continue
    println(items[c])
    c += 1

Syntax sugar (we will keep compulsory data types for now)

for item: int in get_it(): # get_it should return Array[T]
    if item == 2:
        continue
    println(item)

Desugared

yy__1t: Array[int] = get_it()
yy__2t: int = 0
yy__3t: int = len(yk__1t)

while yy__2t < yy__3t:
    ccode """#define yy__item yy__1t[yy__2t]\n// desugar begin"""
    expose_native item: int      # To expose what we put in above C code
    if item == 2:
        yy__2t += 1
        continue                 # Continue must increase the counter
    println(item)
    ccode """#undef yy__item\n// desugar end"""
    yy__2t += 1               # Increase count at the very end

Use case 2 - endless loops ✅

Syntax sugar

for:
    game_step()
    log_stuff()

Desugared

while True:
    game_step()
    log_stuff()

Use case 3 - custom iterators / iterables ⚠️(deferred at this step)

Syntax sugar

def next_book(x: Books) -> Book:
    pass

def has_next_book(x: Books) -> bool:
    pass

def process() -> None:
    books: Books = get_it()
    it: Iterator[Book] = iterator("Book", books, next_book, has_next_book)
    for element: Book in it:
        print_book(element)

Use case 4 - range for loops ⚠️(not required a we have c-like for loops)

Syntax sugar

# Example 1
r: Range[int] = range(1, 5, 2)
for i: int in r:
    if i == 1: # do not print 1
       continue
    println(i)

# Example 2
for i: int in range(1, 5, 2):
    if i == 1: # do not print 1
       continue
    println(i)

Desugared

r: Tuple[int, int, int]
r[0] = 1
r[1] = 5
r[2] = 2

hidden__c = r[0]
while hidden__c < r[1]:
    i: int = hidden__c
    if i == 1:
        hidden__c += r[2]
        continue
    println(i)
    hidden__c += r[2]

Conclusion

Iterators/Ranges are deferred for now. It would be better to come up with a generic Iterator approach for these.

At the moment I think endless loops and simple for-each style loops should be implemented.