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Iterative Control
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There are four types of iterative actions in e:
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- while
- repeat until
- for each in
- for from to
- for
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while
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while loop executed as long as the condition is true.
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Syntax
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while bool-exp [do] {action; ...}
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Example - while
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1 <'
2 extend sys {
3 run() is also {
4 var i : int = 0;
5 while (i < 10) {
6 outf("Current value of i : %x\n",i);
7 i = i + 1;
8 };
9 };
10 };
11 '>
You could download file flow_control4.e
here
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Simulator Output
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Current value of i : 0
Current value of i : 1
Current value of i : 2
Current value of i : 3
Current value of i : 4
Current value of i : 5
Current value of i : 6
Current value of i : 7
Current value of i : 8
Current value of i : 9
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repeat until
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Execute the action block repeatedly in a loop until bool-exp is TRUE. A repeat until action performs the action block at least once. A while action might not perform the action block at all.
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Syntax
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repeat {action; ...} until bool-exp
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Example - repeat until
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1 <'
2 extend sys {
3 run() is also {
4 var i : int = 0;
5 repeat {
6 outf("Current value of i : %x\n",i);
7 i = i + 1;
8 } until (i == 10);
9 };
10 };
11 '>
You could download file flow_control5.e
here
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Simulator Output
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Current value of i : 0
Current value of i : 1
Current value of i : 2
Current value of i : 3
Current value of i : 4
Current value of i : 5
Current value of i : 6
Current value of i : 7
Current value of i : 8
Current value of i : 9
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for each in
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For each item in list-exp, if its type matches type, execute the action block. Inside the action block, the implicit variable it (or the optional item-name) refers to the matched item, and the implicit variable index (or the optional index-name) reflects the index of the current item. If reverse is specified, list-exp is traversed in reverse order, from last to first. The implicit variable index (or the optional index-name) starts at zero for regular loops, and is calculated to start at "(list.size() - 1)" for reverse loops.
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Syntax
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for each [type] [(item-name)] [using index (index-name)]
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in [reverse] list-exp [do] {action; ...}
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Each for each in action defines two new local variables for the loop, named by default it and index. Keep the following in mind:
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- If loops are nested one inside the other, the local variables of the internal loop hide those of the external loop. To overcome this hiding, specify the item-name and index-name with unique names.
- Within the action block, you cannot assign a value to it or index-- or to item-name or index-name.
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Example - for each in
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1 <'
2 struct packet {
3 length: int;
4 keep length < 513;
5 keep length > 63;
6 };
7
8 struct tx_gen {
9 ! packets: list of packet;
10 keep packets.size() == 2;
11 ! packet : packet;
12
13 txgen () is {
14 gen packets;
15 out("--------Generated---------------------");
16 print packets;
17 for each (packet) in packets do {
18 packet_class(packet);
19 };
20 out("--------With it------------------------");
21 for each in packets do {
22 packet_class(it);
23 };
24 out("--------With reverse-------------------");
25 for each in reverse packets do {
26 outf("Current packet position is %d\n", index );
27 packet_class(it);
28 };
29
30 };
31
32 packet_class (pkt : packet) is {
33 outf("Current size of packet : %d\n",pkt.length);
34 };
35 };
36
37 extend sys {
38 U_txgen : tx_gen;
39 run() is also {
40 U_txgen.txgen();
41 };
42 };
43 '>
You could download file flow_control6.e
here
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Simulator Output
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--------Generated---------------------
packets =
item type length
---------------------------------------------------------------------------
0. packet 175
1. packet 479
Current size of packet : 175
Current size of packet : 479
--------With it------------------------
Current size of packet : 175
Current size of packet : 479
--------With reverse-------------------
Current packet position is 1
Current size of packet : 479
Current packet position is 0
Current size of packet : 175
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for from to
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Creates a temporary variable var-name of type int, and repeatedly executes the action block while incrementing (or decrementing if down is specified) its value from from-exp to to-exp in interval values specified by step-exp (defaults to 1).
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In other words, the loop is executed until the value of var-name is greater than the value of to-exp (if down is not specified) or until the value of var-name is less than the value of to-exp (if down is specified).
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Syntax
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for var-name from from-exp [down] to to-exp [step step-exp] [do] {action; ...}
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Example - for from to
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1 <'
2 extend sys {
3 run() is also {
4 var i : int = 0;
5 out ("Loop 1");
6 for i from 2 to 2 * 4 do {
7 out(i);
8 };
9 out ("Loop 2");
10 for i from 1 to 5 step 3 do {
11 out(i);
12 };
13 out ("Loop 3");
14 for i from 7 down to 1 step 2 do {
15 out(i);
16 };
17 };
18 };
19 '>
You could download file flow_control7.e
here
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Simulator Output
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Loop 1
2
3
4
5
6
7
8
Loop 2
1
4
Loop 3
7
5
3
1
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for - C style
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The for loop works similarly to the for loop in the C language. This for loop executes the initial-action once, and then checks the bool-exp. If the bool-exp is TRUE, it executes the action block followed by the step-action. It repeats this sequence in a loop for as long as bool-exp is TRUE.
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- You must enter an initial-action.
- If you use a loop variable within a for loop, you must declare it before the loop (unlike the temporary variable of type int automatically declared in a for from to loop).
- Although this action is similar to a C-style for loop, keep in mind that the initial-action and step-action must be e style actions.
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Syntax
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for {initial-action; bool-exp; step-action} [do] {action; ...}
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Example - for
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1 <'
2 extend sys {
3 run() is also {
4 var i : int = 0;
5 var j : int = 0;
6 for {i=0; i < 15; i = i + 1} do {
7 outf("Current value of i : %d\n",i);
8 outf("Current value of j : %d\n",j);
9 if ( i < 3) {
10 continue;
11 } else {
12 j = j + 1;
13 };
14 if (j > 4) {
15 break;
16 };
17 };
18 };
19 };
20 '>
You could download file flow_control8.e
here
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Simulator Output
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Current value of i : 0
Current value of j : 0
Current value of i : 1
Current value of j : 0
Current value of i : 2
Current value of j : 0
Current value of i : 3
Current value of j : 0
Current value of i : 4
Current value of j : 1
Current value of i : 5
Current value of j : 2
Current value of i : 6
Current value of j : 3
Current value of i : 7
Current value of j : 4
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