looping and branching
Control flow is how you make code execute multiple times, or execute only under certain conditions. Without it, your scripts would be limited to starting at the first line, executing each line exactly once in order, and ending after the last line. MiniScript includes one kind of branching (conditional) structure, and two kinds of loops.
Branching with if
Use an if…then statement to specify some condition under which the following statements should be executed. The basic syntax is:
if condition then
…end if
When the condition is not true, MiniScript will jump directly to the end if statement.
if x == 42 then
print "I have found the Ultimate Answer!"
end ifThe whole set of lines, from if…then to end if, is known as an if block.
Sometimes you want to do something else when the specified condition is not true. You can specify this with an else block before the end if.
if x == 42 then
print "I have found the Ultimate Answer!"
else
print "I am still searching."
end ifFinally, you can check for additional conditions by adding else-if blocks as needed. Here’s a slightly more practical example that converts a number to words.
if apples == 0 then
print "You have no apples."
else if apples == 1 then
print "You have one apple."
else if apples > 10 then
print "You have a lot of apples!"
else
print "You have " + apples + " apples."
end ifIn this case, the first condition that matches will execute its block of lines. If none of the conditions match, then the else block will run instead.
Note that for all these forms, the if, else if, else, and end if statements must each be on its own line. However, there is also a „short form“ if statement that allows you to write an if or if/else on a single line, provided you have only a single statement for the then block, and a single statement for the else block (if you have an else block at all). A shortform if looks like this:if x == null then x = 1
…while a short-form if/else looks like this:if x >= 0 then print "positive" else print "negative"
Notice that end if is not used with a short-form if or if/else. Moreover, there is no way to put more than one statement into the then or else block. If you need more than one statement, then use the standard multi-line form.
Looping with for
A for…in statement loops over a block of code zero or more times. The syntax is:
for variable in list
…end for
The whole block is referred to as a for loop. On each iteration through the loop, the variable is assigned one value from the specified list. You’ll learn more about lists in the Data Types chapter, but for now, it’s enough to know that you can easily create a list of numbers using the range function.
This example counts from 10 down to 1, and then blasts off.
for i in range(10, 1)
print i + "…"
end for
print "Liftoff!"See the range function in the Intrinsic Functions chapter for more options on that.
Instead of a list, you can also iterate over a text string. In this case the loop variable will be assigned each character of the string in order.
Finally, it is also possible to iterate over maps. Again, maps will be explained in the Data Types chapter, but just keep in mind that when you use a for statement with a map, then on each iteration through the loop, your loop variable is a little mini-map containing key and value. For example:
m = {1:"one", 2:"two", 3:"three"}
for kv in m
print "Key " + kv.key + " has value " + kv.value
end forThis prints out each of the key-value pairs in the map.
Looping with while
The other way to loop over code in MiniScript is with a while loop. The syntax is:
while condition
…end while
This executes the contained code as long as condition is true. More specifically, it first evaluates the condition, and if it’s not true, it jumps directly to end while. If it is true, then it executes the lines within the loop, and then jumps back up to the while statement. The process repeats forever, or until the condition becomes false.
This is illustrated by the very first example in this manual, repeated here.
s = "Spam"
while s.len < 50
s = s + ", spam"
end while
print s + " and spam!"This code builds a string (s) by adding more spam to it, as long as the string length is less than 50. Once it is no longer less than 50, the loop exits, and the result is printed.
Break and Continue
There are two additional keywords that let you bail out of a while or for loop early. First, the break statement jumps directly out of the loop, to the next line past the end for or end while. Consider the following.
while true // loops forever!
if time > 100 then break
end whileWhenever you see while true (or while 1, which is equivalent), it is an infinite loop — unless there is a break statement in the body of the loop. As soon as that break statement executes, we jump directly out of the loop. It works for for loops in exactly the same way. In the case of nested loops, break breaks out of only the innermost loop.
The continue statement skips the rest of the body of the loop, and proceeds with the next iteration. This is often used for „bail-out“ cases in a large loop, where under certain conditions you want to skip an iteration and just go on with the next one.
for i in range(1,100)
if i == 42 then continue
print "Considering " + i + "…"
end forThis will print out the numbers 1 through 100, except for 42, which is skipped. Note that if you simply changed continue to break in this example, the loop would print the numbers 1 through 41, and then stop.
The Nature of Truth
We have talked about evaluating conditions as true or false, without explaining what that really means. Usually you don’t need to worry about it, but here are the details anyway.
Boolean (true/false) values in MiniScript are represented as numbers. When conditions are evaluated for if and while statements, a value of 0 (zero) is considered false; and other value is considered true. In fact the built-in keywords true and false are exactly equivalent to the numbers 1 and 0 respectively.
When you use comparison operators such as == (equal), != (not equal), > (greater than), and <= (less than or equal), these compare their operands and evaluate to either 1 (if true) or 0 (if false).
See the Numbers section of the Data Types chapter for more boolean operations you can apply to numbers (including and, or, and not).
Finally, in a context that demands a truth value — that is, in an if and while statement, or as an operand of and, or, and not — other data types will be considered false if they are empty, and true if they are not empty. So an empty string, list, or map is equivalent to 0 (zero), and any non-empty string, list or map is equivalent to 1 in these contexts. The special value null is always considered false.
