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Collection manipulation

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Wang Renxin edited this page May 31, 2022 · 32 revisions

MY-BASIC supplies a set of LIST, DICT manipulation function libraries which offer creation, accessing, iteration, etc. as follow:

Name Description
LIST Creates a list
DICT Creates a dictionary
PUSH Pushes a value to the tail of a list, overridable for referenced usertype and class instance
POP Pops a value from the tail of a list, overridable for referenced usertype and class instance
BACK Peeks the value of a tail of a list, overridable for referenced usertype and class instance
INSERT Inserts a value at a specific position of a list, overridable for referenced usertype and class instance
SORT Sorts a list increasingly, overridable for referenced usertype and class instance
EXISTS Tells whether a list contains a specific value (not index), or whether a dictionary contains a specific key, overridable for referenced usertype and class instance
INDEX_OF Gets the index of a value in a list, overridable for referenced usertype and class instance
GET Returns the value of a specific index in a list, or the value of a specific key in a dictionary, or a member of a class instance, overridable for referenced usertype and class instance
SET Sets the value of a specific index in a list, or the value of a specific key in a dictionary, or a member variable of a class instance, overridable for referenced usertype and class instance
REMOVE Removes the element of a specific index in a list, or the element of a specific key in a dictionary, overridable for referenced usertype and class instance
CLEAR Clears a list or a dictionary, overridable for referenced usertype and class instance
CLONE Clones a collection, or a referenced usertype
TO_ARRAY Copies all elements from a list to an array
ITERATOR Gets an iterator of a list or a dictionary, overridable for referenced usertype and class instance
MOVE_NEXT Moves an iterator to next position for a list or a dictionary, overridable for referenced usertype and class instance

Besides, it's also possible to apply some other generic function to collections:

Name Description
TYPE Gets the type string of a value, overridable for referenced usertype and class instance
VAL Returns the number type value of a string, or the value of a dictionary iterator, overridable for referenced usertype and class instance
LEN Gets element count of a collection, overridable for referenced usertype and class instance

For example:

l = list(1, 2, 3, 4)
set(l, 1, “b”)
print exists(l, 2); pop(l); back(l); len(l);

d = dict(1, “one”, 2, “two”)
set(d, 3, “three”)
print len(d)
it = iterator(d)
while move_next(it)
	print get(it);
wend

It's possible to implement other collection functions with built-in ones.

A REVERSED function as:

def reversed(l)
	if not l is type("list") then
		return nil
	endif

	ret = list()
	while len(l) <> 0
		push(ret, pop(l))
	wend

	return ret
enddef

CAR and CDR:

def car(l)
	if not (l is type("list")) then
		return nil
	endif

	if len(l) = 0 then
		return nil
	endif

	return l(0)
enddef

def cdr(l)
	if not (l is type("list")) then
		return nil
	endif

	if len(l) = 0 then
		return nil
	endif

	ret = clone(l)
	remove(ret, 0)

	return ret
enddef

A JOIN_STR function:

def join_str(lst, sep)
	ret = ""
	l = len(lst)
	for i = 0 to l - 1
		ret = ret + lst(i)
		if i <> l - 1 then
			ret = ret + sep
		endif
	next

	return ret
enddef

Sorted iterator for dictionary, with usage:

class iterator_node
	var key = nil
	var value = nil
endclass

def sorted_iterator(d)
	l = list()
	i = iterator(d)
	while move_next(i)
		push(l, get(i))
	wend
	sort(l)

	i = iterator(l)
	n = new(iterator_node)

	return lambda()
	(
		if not move_next(i) then
			return nil
		endif

		k = get(i)
		n.key = k
		n.value = d(k)

		return n
	)
enddef

d = dict()
d(1) = "uno"
d(2) = "dos"
d(3) = "thres"
i = sorted_iterator(d)
p = i()
while p
	print p.key, ", ", p.value;
	p = i()
wend

It's also possible to visit each value in a list or each key in a dictionary using the FOR IN statement, besides using iterators. For example:

l = list(1, 2, 3, 4, 5)
for i in l
	print i;
next

d = dict(1, 2, 3, 4, 5, 6)
for i in d
	print i, ", ", d(i);
next

Use the TO statement to create a ranged list with integers as:

list(100 to 0)
list(0 to 100)

Read the Stack module page to get information about how to implement a stack collection.

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