Method parseIf

chapter07/src/main/java/com/seaofnodes/simple/Parser.java:220–257

Parses a statement if ( expression ) statement [else statement] @return a Node, never null

()

     * @return a {@link Node}, never {@code null}
     */
    private Node parseIf() {
        require("(");
        // Parse predicate
        var pred = require(parseExpression(), ")");
        // IfNode takes current control and predicate
        IfNode ifNode = (IfNode)new IfNode(ctrl(), pred).<IfNode>keep().peephole();
        // Setup projection nodes
        Node ifT = new ProjNode(ifNode, 0, "True" ).peephole();
        ifNode.unkeep();
        Node ifF = new ProjNode(ifNode, 1, "False").peephole();
        // In if true branch, the ifT proj node becomes the ctrl
        // But first clone the scope and set it as current
        int ndefs = _scope.nIns();
        ScopeNode fScope = _scope.dup(); // Duplicate current scope
        _xScopes.push(fScope); // For graph visualization we need all scopes

        // Parse the true side
        ctrl(ifT);              // set ctrl token to ifTrue projection
        parseStatement();       // Parse true-side
        ScopeNode tScope = _scope;

        // Parse the false side
        _scope = fScope;        // Restore scope, then parse else block if any
        ctrl(ifF);              // Ctrl token is now set to ifFalse projection
        if (matchx("else")) {
            parseStatement();
            fScope = _scope;
        }

        if( tScope.nIns() != ndefs || fScope.nIns() != ndefs )
            throw error("Cannot define a new name on one arm of an if");

        // Merge results
        _scope = tScope;
        _xScopes.pop();       // Discard pushed from graph display

        return ctrl(tScope.mergeScopes(fScope));
    }


    /**