selfhost: port switch — N_SWITCH parser + cgen + scratch slot

lib/ww/parse/stmt.ww

@@ -176,6 +176,63 @@ fn parsefor(p: *parser) *node = {
 	return n;
 };
 
+fn parseswitch(p: *parser) *node = {
+	let pf: str = p.curfile;
+	let pl: i32 = p.curline;
+	let pc: i32 = p.curcol;
+	advance(p);	// past `switch`
+	expecttok(p, tkind.TK_LPAREN, "expected '(' after switch");
+	let n: *node = newnode(p.a, nkind.N_SWITCH, pf, pl, pc);
+	n.lhs = parseexpr(p);
+	expecttok(p, tkind.TK_RPAREN, "expected ')' after switch expression");
+	expecttok(p, tkind.TK_LBRACE, "expected '{' to open switch body");
+	let head: *node = nil;
+	let tail: *node = nil;
+	for (p.curkind == tkind.TK_CASE) {
+		let cpf: str = p.curfile;
+		let cpl: i32 = p.curline;
+		let cpc: i32 = p.curcol;
+		advance(p);	// past `case`
+		let cs: *node = newnode(p.a, nkind.N_CASE, cpf, cpl, cpc);
+		let eh: *node = nil;
+		let et: *node = nil;
+		if (p.curkind != tkind.TK_COLON) {
+			p.nocast = 1;
+			for (true) {
+				let e: *node = parseexpr(p);
+				if (eh == nil) { eh = e; }
+				else { et.next = e; };
+				et = e;
+				if (!accepttok(p, tkind.TK_COMMA)) { break; };
+			};
+			p.nocast = 0;
+		};
+		cs.list = eh;
+		expecttok(p, tkind.TK_COLON, "expected ':' after case label");
+		let bh: *node = nil;
+		let bt: *node = nil;
+		for (p.curkind != tkind.TK_CASE) {
+			if (p.curkind == tkind.TK_RBRACE) { break; };
+			if (p.curkind == tkind.TK_EOF) { break; };
+			let s: *node = parsestmt(p);
+			if (s != nil) {
+				if (bh == nil) { bh = s; }
+				else { bt.next = s; };
+				bt = s;
+			};
+		};
+		let blk: *node = newnode(p.a, nkind.N_BLOCK, cpf, cpl, cpc);
+		blk.list = bh;
+		cs.body = blk;
+		if (head == nil) { head = cs; }
+		else { tail.next = cs; };
+		tail = cs;
+	};
+	expecttok(p, tkind.TK_RBRACE, "expected '}' to close switch");
+	n.list = head;
+	return n;
+};
+
 fn parsestmt(p: *parser) *node = {
 	let pf: str = p.curfile;
 	let pl: i32 = p.curline;
@@ -202,6 +259,11 @@ fn parsestmt(p: *parser) *node = {
 		expecttok(p, tkind.TK_SEMI, "expected ';' after for");
 		return n;
 	};
+	if (p.curkind == tkind.TK_SWITCH) {
+		let n: *node = parseswitch(p);
+		expecttok(p, tkind.TK_SEMI, "expected ';' after switch");
+		return n;
+	};
 	if (p.curkind == tkind.TK_RETURN) {
 		advance(p);
 		let n: *node = newnode(p.a, nkind.N_RETURN, pf, pl, pc);