Turn [-] or [+] into a clear command

README.md

@@ -14,3 +14,4 @@ Gir can parse and prettyprint to Javascript console programs in brainfuck.
 Gir supports following optimizations:
 
 * Turn runs of +- or <> into one command
+* Turn [-] or [+] into one command

gir.js

@@ -18,6 +18,9 @@ const readByte = Symbol('readByte');
 // [-] → {type: loop, contents: [{type: add, value: -1}]}
 const loop = Symbol('loop');
 
+// [-] → {type: clear}
+const clear = Symbol('clear');
+
 // TODO: Add extensions from Eldis
 
 // ------------------------------------------------------------------
@@ -78,7 +81,10 @@ function parse(program) {
 					}
 				}
 
-				commands.push({type: add, value: value});
+				// Only add the command is value is not 0
+				if(value != 0) {
+					commands.push({type: add, value: value});
+				}
 				// i is not incremented, since it already
 				// points to a location containig a char we
 				// have not yet handled
@@ -97,7 +103,10 @@ function parse(program) {
 					}
 				}
 
-				commands.push({type: moveHead, value: value});
+				// Only add the command is value is not 0
+				if(value != 0) {
+					commands.push({type: moveHead, value: value});
+				}
 				// see +/- for why we don't increment i
 
 			} else if(program[i] == '.') {
@@ -162,6 +171,9 @@ function prettyPrint(parsed) {
 				line += 'loop';
 				console.log(line);
 				printIndented(command.contents, indent + '  ');
+			} else if(command.type == clear) {
+				line += 'clear';
+				console.log(line);
 			} else {
 				line += `unknown ${command.type}`;
 				console.log(line);
@@ -219,6 +231,33 @@ function joinAdjacentOps(parsed) {
 }
 
 // ([commandObjects]) → [commandObjects]
-function optimize(parsed) {
-	return joinAdjacentOps(parsed);
+function transformClearLoops(parsed) {
+	let optimized = [];
+
+	for(let command of parsed) {
+		// Only match loops like [-] or [+]
+		let isClearLoop = command.type == loop &&
+			command.contents.length == 1 &&
+			command.contents[0].type == add &&
+			(command.contents[0].value == 1 ||
+			command.contents[0].value == -1);
+		if(isClearLoop) {
+			optimized.push({type: clear});
+		} else if(command.type == loop) {
+			// Run for inner loops
+			optimized.push({type: loop,
+				contents: transformClearLoops(command.contents)});
+		} else {
+			optimized.push(command);
+		}
+	}
+
+	return optimized;
+}
+
+// ([commandObjects]) → [commandObjects]
+function optimize(parsed) {
+	const optimizations = [joinAdjacentOps, transformClearLoops];
+	return optimizations.reduce((IR, optimization) =>
+		optimization(IR), parsed);
 }