switch.xxl

// -*-js-*-

var __doc = """
EXTENSION: switch statement
""";

// *BEWARE*! uses Symbol.default, Symbol.case properties
//	which will not be dumped!!

var __extend_parser = function (p) {
    const CASEVAR = '-*-case-*-';

    var Switch = Class.new({
	name: "Do",
	supers: [p.Stmt],
	methods: {
	    std: function (this) {	// parse as statement
		p.advance("(");
		this.first = p.expression(0);
		var slist = [];
		p.advance(")");
		p.advance("{");
		var prev_default;
		while (!p.check("}")) {
		    var tok = p.ctoken();
		    if (p.check("case")) {
			p.reserve(tok);
			p.advance();
			tok.first = p.expression(0);
			tok.case = true; // XXX not visible in AST dump
			// XXX set tok.arity?
			p.advance(":");
		    }
		    else if (p.check("default")) {
			p.reserve(tok);
			if (prev_default) {
			    tok.error("previous default label at " +
				      prev_default.where);
			}
			prev_default = tok;
			tok.default = true; // XXX not visible in AST dump
			// XXX set tok.arity?
			p.advance();
			p.advance(":");
		    }
		    else {
			tok = p.statement();
		    }
		    slist.append(tok);
		}
		p.advance("}");
		this.second = slist;
		this.arity = "statement";
		return(this);
	    },
	    gen: function (this, vmcode) { // gen
		var swcode = p.VMCode.new(); // switch VMcode block
		swcode.emit_scope(null, this); // scope for switch
		swcode.emit_var(CASEVAR, this); // create variable for value
		this.first.gen(swcode);		// evaluate switch expr
		swcode.emit_store(CASEVAR, this); // store in variable

		// XXX should "hoist" emit_var (but not init) to top of block?!

		// emit tests/branches
		this.second.for_each(
		    function (item) {
			if (item.case) {
			    swcode.gen_push(item.first);
			    swcode.emit_load(CASEVAR, item);
			    swcode.emit_binop("==", item);
			    item.label = swcode.def_fwd_label();
			    swcode.emit_iftrue(item.label, item);
			}
		    } // function (item)
		); // for_each

		// end of tests, go to default
		var default_label = swcode.def_fwd_label();
		swcode.emit_jrst(default_label, this);

		// run thru stmts, dropping labels or code
		this.second.for_each(
		    function (item) {
			if (item.case) {
			    swcode.drop_fwd_label(item.label);
			}
			else if (item.default) {
			    swcode.drop_fwd_label(default_label);
			    default_label = null;
			}
			else {
			    item.gen(swcode);
			}
		    }
		);

		// if no default label seen, drop at end of block.
		if (default_label !== null) {
		    swcode.drop_fwd_label(default_label);
		}

		// create block closure & invoke
		vmcode.emit_bclose_call(swcode, this);
	    } // gen
	}
    });
    p.add_symbol_class("switch", Switch);
};