add Loops

2 files changed, 114 insertions, 0 deletions

diff --git a/Loops/README.md b/Loops/README.md
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+# Loops
+
+Looping in Limbo is similar to looping in C. Supported loop formats are for, while, and do-while. 
+
+## Source
+
+### loops.b:18,23
+
+	for(i := 0; i < 10; i++){
+		if(i % 2 == 0)
+			continue;
+
+		print("%d\n", i * i);
+	}
+
+A for loop consists of an initialization, qualification, operation, and post-iteration sequence. 
+
+Before the loop begins, but before the initial check, `i := 0` is run.
+
+After each loop iteration, `i++` is performed, then `i < 10` is checked. 
+
+The `continue` keyword, from the point it is called, skips to the next loop iteration. In this case, `continue` is called if `i` is an even number. If `i` is an odd number, `i²` is printed. 
+
+Note that the `continue` keyword does not skip the post-iteration operation. 
+
+### loops.b:28,29
+
+	while(n)
+		print("%d\n", n--);
+
+A while loop will check the qualifier for whether to enter another iteration, then, perform its operation. This loop will print the value of `n` in the range [7,1]. 
+
+Note that in this case the braces are omitted.
+
+### loops.b:33,36
+
+	do{
+		print("%d\n", ++n);
+		break;
+	}while(1);
+
+A do-while loop will perform its operation, then check the qualifier for whether to enter another iteration. In this case, the qualifier is a constant which is quantified as a true value, so, this loop would iterate forever.
+
+The `break` keyword interrupts iterative processing. In this case, it terminates the loop immediately after the print on its first iteration. 
+
+Note that we reuse the value of `n`, In this case, the incremented value of `n` is printed, as when the preceding loop ends, the value of `n` is 0. 
+
+## Demo
+
+	; limbo loops.b
+	; loops
+	== for
+	1
+	9
+	25
+	49
+	81
+	== while
+	7
+	6
+	5
+	4
+	3
+	2
+	1
+	== do
+	1
+	; 
+
+## Exercises
+
+- Try reversing the ++/-- operators in different places, what happens?
+- Try omitting various portions of the for loop syntax, what happens?
+- Is `for(;;);` an infinite loop?
+- Make the condition for a loop something similar to --n, how many iterations does it run for?
diff --git a/Loops/loops.b b/Loops/loops.b
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+++ b/Loops/loops.b
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+implement Loops;
+
+include "sys.m";
+include "draw.m";
+
+sys: Sys;
+print: import sys;
+
+Loops: module {
+	init: fn(nil: ref Draw->Context, nil: list of string);
+};
+
+init(nil: ref Draw->Context, nil: list of string) {
+	sys = load Sys Sys->PATH;
+
+	print("== for\n");
+
+	for(i := 0; i < 10; i++){
+		if(i % 2 == 0)
+			continue;
+
+		print("%d\n", i * i);
+	}
+
+	print("== while\n");
+
+	n := 7;
+	while(n)
+		print("%d\n", n--);
+
+	print("== do\n");
+
+	do{
+		print("%d\n", ++n);
+		break;
+	}while(1);
+
+	exit;
+}