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 +======Synopsis:​======
 +[[for]] (//once//, //​expression//,​ //each//) { //​[[block]]//​ } \\ 
 +[[for]] //var// from //​firstval//​ to //lastval// { //​[[block]]//​ } \\
 +[[for]] //var// from //​firstval//​ to //lastval// step //stepval// { //​[[block]]//​ } \\
 +[[for]] //var// in (//word list//) { //​[[block]]//​ }
 +
 +======Description (standard form):​======
 +[[FOR]] is a general purpose loop.  It is modeled on the C for statement,
 +and works in a very similar manner. ​ Aside from the action, there are
 +three parts to a [[FOR]] loop:
 +
 +The //once// part is a //​[[block]]//​ executed before the loop begins ​
 +iterating. ​ This is often used for initializing counters and other 
 +variables that will be used in the loop.
 +
 +Before each loop iteration, the //​condition//​ expression is checked.  ​
 +Most often, this is used to see if the counter has exceeded a certain limit.  ​
 +The condition may contain any expression legal in the [[IF]] command.
 +Because of this, the loop does not necessarily have to iterate at all.
 +
 +The //each// part is a //​[[block]]//​ executed each time the loop exits and
 +before the //​condition//​ is tested. ​ This is where you would increment a
 +counter that gets checked by the condition statement.
 +
 +It is imperative to note that the three sections are separated by commas
 +and not semicolons; this is because //once// and //each// may contain ​
 +semicolons if they contain multiple statements. ​ This is the reverse of C.
 +The first and third section are **COMMANDS** and the second section is an
 +**EXPRESSION**.
 +
 +//Once//, //each//, and //block// are optional and may be left blank.
 +
 +======Description (for/next form):​======
 +This second form of the command provides a FOR .. NEXT type loop that
 +enumerates each of the integers between //​firstval//​ and //​lastval//​.
 +Each enumerated integer is assigned to //var// and the //block// is 
 +executed.
 +
 +If you wish enumerate only some of the values in the range, you can 
 +specify a //step//, which says that each //step//th value should be 
 +enumerated.
 +
 +If //​firstval//​ is greater than //lastval// then you must specify a 
 +//step// value and it must be negative. ​ If you do not do this, then
 +the loop will not execute.
 +
 +The //var// variable should be considered read-only. ​ Changing it will
 +**not** affect how the range is enumerated.
 +
 +This form is much cheaper than a standard [[for]], and is cheaper than a [[fe]]
 +over a [[jot]] range.
 +
 +The [[CONTINUE]] and [[BREAK]] commands are honored in the action body.
 +The [[CONTINUE]] command will behave as a "​next"​ operation, and the [[BREAK]]
 +command will abort the loop entirely.
 +
 +======Description (for/each form):​======
 +This third and final form is a FOR .. IN LIST type loop that iterates over
 +each word in the word list, assiging each value in turn to the //var// and
 +executing the //block//.
 +
 +This form is cheaper than [[fe]] because it is optimized for iterating ​
 +one word at a time, whereas [[fe]] is general-purpose.
 +
 +The [[CONTINUE]] and [[BREAK]] commands are also honored in the same way
 +as in the second form above.
 +
 +======Examples:​======
 +Form 1:
 +
 +To display a warning message 3 times:
 +      for ( @ xx = 3, xx > 0, @ xx-- ) {
 +         echo WARNING! ​ This ship will self destruct in $xx seconds!
 +      }
 +
 +A infinite loop that behaves like the Unix '​yes'​ command:
 +      for ( ,, ) {
 +         echo yes
 +      }
 +
 +Form 2:
 +
 +Display the numbers 1 through 5 each on a separate line:
 +      for ii from 1 to 5 {
 +         echo $ii
 +      }
 +
 +Display the numbers 1, 3, and 5 each on a separate line:
 +      for ii from 1 to 5 step 2 {
 +         echo $ii
 +      }
 +
 +Form 3:
 +
 +Display the words "​one",​ "​two",​ and "​three"​ each on a separate line:
 +      for xx in (one two three) {
 +         echo $xx
 +      }
 +
 +======History:​======
 +
  
for.txt ยท Last modified: 2006/08/01 03:13 (external edit)