Extract a canonical version of the input
function() {
        var line = [];
        line.push(this.commandAssignment.value.name);
        Object.keys(this._assignments).forEach(function(name) {
            var assignment = this._assignments[name];
            var type = assignment.param.type;
            // TODO: This will cause problems if there is a non-default value
            // after a default value. Also we need to decide when to use
            // named parameters in place of positional params. Both can wait.
            if (assignment.value !== assignment.param.defaultValue) {
                line.push(' ');
                line.push(type.stringify(assignment.value));
            }
        }, this);
        return line.join('');
    }