Matlab – Wanted: Matlab example of an anonymous function returning more than 1 output

It doesn't work because it is being parsed as a FunctionDeclaration, and the name identifier of function declarations is mandatory.

When you surround it with parentheses it is evaluated as a FunctionExpression, and function expressions can be named or not.

The grammar of a FunctionDeclaration looks like this:

function Identifier ( FormalParameterListopt ) { FunctionBody }

And FunctionExpressions:

function Identifieropt ( FormalParameterListopt ) { FunctionBody }

As you can see the Identifier (Identifieropt) token in FunctionExpression is optional, therefore we can have a function expression without a name defined:

(function () {
    alert(2 + 2);
}());

Or named function expression:

(function foo() {
    alert(2 + 2);
}());

The Parentheses (formally called the Grouping Operator) can surround only expressions, and a function expression is evaluated.

The two grammar productions can be ambiguous, and they can look exactly the same, for example:

function foo () {} // FunctionDeclaration

0,function foo () {} // FunctionExpression

The parser knows if it's a FunctionDeclaration or a FunctionExpression, depending on the context where it appears.

In the above example, the second one is an expression because the Comma operator can also handle only expressions.

On the other hand, FunctionDeclarations could actually appear only in what's called "Program" code, meaning code outside in the global scope, and inside the FunctionBody of other functions.

Functions inside blocks should be avoided, because they can lead an unpredictable behavior, e.g.:

if (true) {
  function foo() {
    alert('true');
  }
} else {
  function foo() {
    alert('false!');
  }
}

foo(); // true? false? why?

The above code should actually produce a SyntaxError, since a Block can only contain statements (and the ECMAScript Specification doesn't define any function statement), but most implementations are tolerant, and will simply take the second function, the one which alerts 'false!'.

The Mozilla implementations -Rhino, SpiderMonkey,- have a different behavior. Their grammar contains a non-standard Function Statement, meaning that the function will be evaluated at run-time, not at parse time, as it happens with FunctionDeclarations. In those implementations we will get the first function defined.

Functions can be declared in different ways, compare the following:

1- A function defined with the Function constructor assigned to the variable multiply:

var multiply = new Function("x", "y", "return x * y;");

2- A function declaration of a function named multiply:

function multiply(x, y) {
    return x * y;
}

3- A function expression assigned to the variable multiply:

var multiply = function (x, y) {
    return x * y;
};

4- A named function expression func_name, assigned to the variable multiply:

var multiply = function func_name(x, y) {
    return x * y;
};

There's no way I know of within the expression of the anonymous function to have it select which output to return from a function with multiple possible output arguments. However, you can return multiple outputs when you evaluate the anonymous function. Here's an example using the function MAX:

>> data = [1 3 2 5 4];  %# Sample data
>> fcn = @(x) max(x);   %# An anonymous function with multiple possible outputs
>> [maxValue,maxIndex] = fcn(data)  %# Get two outputs when evaluating fcn

maxValue =

     5         %# The maximum value (output 1 from max)


maxIndex =

     4         %# The index of the maximum value (output 2 from max)

Also, the best way to handle the specific example you give above is to actually just use the function handle @ttest2 as the input to CELLFUN, then get the multiple outputs from CELLFUN itself:

[junk,probabilities] = cellfun(@ttest2,cellArray1,cellArray2);

On newer versions of MATLAB, you can replace the variable junk with ~ to ignore the first output argument.