ReNamer:Pascal Script:Quick guide

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If you are not familiar with Pascal Scripting, first go through the excellent tutorial written by Tao Yue.

The following is a short overview of Pascal Script.

Basic pascal script

The structure of a basic script is as follows (keywords are shown in ALLCAPS bold):

CONST

<Constant declarations>

TYPE

<Type declarations>

VAR

<Variable declarations>

BEGIN

<Executable statements>

END.

Note that:

  • The main code must be within the begin and end. keywords.
  • All statements in the script use the semicolon ";" as terminator. Only the last statement (END.) uses a dot as terminator.

Control structures

All the typical control structures (building blocks) occurring in Pascal Script are described in the following table. The table shows a flow chart and Pascal Script code required to implement that logic. To compose your own PascalScript rule, you can simply copy and paste the code and then edit it to finish your script.

In actual implementation, just substitute the following:

  • Replace <Condition> with an actual Pascal statement that tests for a condition.
  • Replace <Action> with code block that takes action relevant to the condition. There may be several statements.

Branching

These structures are used to execute different blocks of code depending upon a condition.

Branching structure Pascal script Flowchart (Logic) Remarks
if-then 
if <Condition> then 
begin 
  <Action> 
end;
PascalScriptIfThen.png

Execute the <Action> statement only if the <Condition> is met. Otherwise pass on the control to the next statement that follows the <Action>.

if-then-else 
if <Condition> then 
begin 
  <Action-1> 
end else 
begin 
  <Action-2> 
end;
PascalScriptIfThenElse.png

Two alternative actions are provided.

If <Condition> is met, execute <Action-1>. Otherwise execute <Action-2>.

Thus one of these two <Actions> are definitely executed.

After execution of the action, pass on the control to the next statement.

case/switch 
case X of 
  1:
    begin 
      <Action-1> 
    end; 
  2:
    begin 
      <Action-2> 
    end; 
  else
    begin 
      <Default Action> 
    end; 
end;
PascalScriptCase.png


This code structure has several <Action> blocks, each with its own condition.

  • Any given <Action> block is executed only if its condition is met.
  • One and only one <Action> is executed. After that, the control passes on to the next statement. (It does not check for the next condition.)
  • The conditions are checked in the "top down" order. So even if the other conditions are also met, their <Actions> will never be executed.
  • The code structure can optionally have a <Default Action>. It is executed if (and only if-) none of the conditions are met.

This is a generalized version of the if-then-else block (above).

Loops

Loops are used to execute a block of code iteratively till a certain condition is met.

Loops Pascal script Flowchart (Logic) Remarks
For To Do 
for I := X to Y do 
begin 
  <Action> 
end;
PascalScriptForLoop.png
 Execute the <Action> a certain number of times.

This example shows that the counter is incremented by 1, but it can be any statement that changes the value of the counter vaiable towards the target value.

Similarly, the decision block can have any logical expression with the counter.

Make sure that the exit condition is reached at some point of time; otherwise the loop will execute endlessly, and ReNamer will appear to be hung.

While Do 
while <Condition> do 
begin 
  <Action> 
end;
PascalScriptWhileLoop.png
 Check for a condition and if it is met, execute the <Action>.

The loop is repeated till the condition is met. When the condition is not met, the loop is terminated and control passes to the next statement. Note that if the condition fails in the first-ever check, the <Action> may not be executed at all.

Make sure that the condition will fail at some point of time; otherwise the loop will execute endlessly, and ReNamer will appear to be hung.

Sometimes the condition is set to be always TRUE, and then a statement inside the <Action> block breaks the loop based on a different condition.(See the break command below)

Repeat Until 
repeat 
  <Action> 
until <Condition>;
PascalScriptRepeatUntilLoop.png
 This structure is similar to the While loop (see above). However, the only difference is that the <Action> is taken first and then the condition is checked. As a result, the <Action> is executed at least once.
Break 
Break;

OR

if <Condition> then Break;

This statement is placed in any of the above loops to terminate the loop when a condition is met. Typically, it is used as the <Action> statement in a if-then block. This block is then embedded (nested) inside the other code block that is to be contionally terminated.

See the Case block above, which uses the break statement as integral part of its structure.

Continue 
Continue;

OR 

if <Condition> then Continue;

This statement is placed in any of the above loops to jump to the end of the current iteration, bypassing all the subsequent statements within the loop. However, the execution of the loop continues (the next iteration starts).

Typically, it is used as the <Action> statement in a if-then block. This block is then embedded (nested) inside the other code block, just before the statements that are to be skipped in the current iteration.

Control

Exit 
Exit;

OR 

if <Condition> then Exit;

The Exit procedure abruptly terminates the current function or procedure. If exiting a function, then Result contains the last set value.

Warning: use with caution - jumping is a concept at odds with structured coding - it makes code maintenance difficult.

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