10.2.3 Conditional Construct Symbols

Here is a (totally contrived) example which illustrates how syntax is assigned to various conditional constructs:

 1: void spam( int index )
 2: {
 3:     for( int i=0; i<index; i++ )
 4:     {
 5:         if( i == 10 )
 6:             do_something_special();
 7:         else
 8:           silly_label:
 9:             do_something( i );
10:     }
11:     do {
12:         another_thing( i-- );
13:     }
14:     while( i > 0 );
15: }

Only the lines that illustrate new syntactic symbols will be discussed.

Line 4 has a brace which opens a conditional’s substatement block. It is thus assigned substatement-open syntax, and since line 5 is the first line in the substatement block, it is assigned statement-block-intro syntax. Line 10 contains the brace that closes the inner substatement block, and is therefore given the syntax block-close38. Line 13 is treated the same way.

Lines 6 and 9 are also substatements of conditionals, but since they don’t start blocks they are given substatement syntax instead of substatement-open.

Line 8 contains a label, which is normally given label syntax. This one is however a bit special since it’s between a conditional and its substatement. It’s analyzed as substatement-label to let you handle this rather odd case differently from normal labels.

Line 7 start with an else that matches the if statement on line 5. It is therefore given the else-clause syntax and is anchored on the matching if. The try-catch constructs in C++ and Java are treated this way too, except that catch and (in Java) finally, are marked with catch-clause.

The while construct on line 14 that closes a do conditional is given the special syntax do-while-closure if it appears on a line by itself. Note that if the while appeared on the same line as the preceding close brace, that line would still have block-close syntax.



block-open is used only for “free-standing” blocks, and is somewhat rare (see Comment String Label and Macro Symbols for an example.)