In fact, I found a solution!

My problem was:

After some processing on data (user and not) I get Strings filled with expression like 'true AND false' or '(true AND true) OR false' in the controller of one of my visualforce pages. From this, the problem was to find a solution to evaluate these Strings and return the boolean result for each of them.

List<String> expressions;

// Some Processing on data to fill expressions
// e.g. expressions[0] = 'true AND false'
// e.g. expressions[1] = '(true AND true) OR false'

List<Boolean> ret = new List<Boolean>();

for(String s : expressions)
{
   ret.add(eval(s)); // ?????
}

for(Boolean b : ret)
{
   if (b)
   {
      // Some processing
   }
}

My solution (maybe not the best one but it works):

All the first processing on data is performed in a @RemoteAction static method of my controller.

This method is called by a Javascript (javascript executed on page load) to retrieve the list of expressions to evaluate.

For each String, the script uses its 'eval' function and add the result in a return list.

Finally the script calls another method from the controller (not static this time) via an apex:actionFunction to send back the results which can now be processed in my controller.

Controller:

@RemoteAction
public static List<String> first()
{
   List<String> expressions = new List<String>();
   //Build list of expression via processing on data
   return expressions;
}

public PageReference handleReturn()
{
    String returnedList = Apexpages.currentPage().getParameters().get('returnedList');
    // Processing
}

Visualforce page :

<apex:page standardController="XXX" extensions="YYY">
    <script>
    window.onload = function() 
        { 
            if (!{!evalDone}) 
            { 
                var lstRet  = '';
                var idValue = '{!param}';
                
                YYY.first(idValue, function(result, event)
                {
                    var listStr = result;

                    for (var x = 0; x < listStr.length; x++)
                    {
                        var res = eval(listStr[x]);
                        lstRet = lstRet + res;
                        lstRet = lstRet + ';';
                    }
                    
                    handleReturn(lstRet);
                }, {escape:true}); 
            }
        }
</script>
    <apex:form >
        <apex:actionFunction action="{!handleReturn}" name="handleReturn" rerender="view">
            <apex:param id="aname" name="returnedList" value="" />
        </apex:actionFunction>
        ...
    </apex:form>
</apex:page>