View source for ElementaryBlock Element/en

=== Example: Simple String Processing ===

The first example simply takes a string and cuts off some characters at either side, and returns some middle part of it. To make the example more interesting, the parts to be cut off shall be the first 5 characters at the left, and everything after the last separator (blank character or tab).
Be reminded that a similar action is available in the standard library - the example below is here to describe how it can be done.

We first define the external interface of that action block to consist of an input-pin named "''inString''" and an output-pin named "''outString''". Both pins are declared as being of "<code>String</code>"-datatype, this ensures, that when placed into a diagram, only other String-typed pins can be connected to it.
The so called "''schema''" definition of the action block is therefore:<br>
[[Bild: string_example_elementaryBlock.png]]
<br>Then, write the code, either in [[Expecco_API | Smalltalk]] as:
 execute
    |inStringValue indexOfLastSeparator middlePart|
 
    <span style="color:#007F00">"/ fetch the data value from the pin</span>
    <span style="color:#007F00">"/ notice that inString refers to the pin - not the value</span>
    inStringValue := inString value.
 
    <span style="color:#007F00">"/ find the last separator in the string</span>
    indexOfLastSeparator := inStringValue lastIndexOfSeparator.
 
    <span style="color:#007F00">"/ extract the middle part</span>
    middlePart := inStringValue copyFrom:6 to:(indexOfLastSeparator-1).
 
    <span style="color:#007F00">"/ write to the output pin</span>
    outString value: middlePart

The same operation written in JavaScript as:
 execute() {
    var inStringValue, indexOfLastSeparator, middlePart;
 
    <span style="color:#007F00">// fetch the data value from the pin</span>
    inStringValue = inString.value();
 
    <span style="color:#007F00">// find the last separator in the string</span>
    indexOfLastSeparator = inStringValue.lastIndexOfSeparator();
 
    <span style="color:#007F00">// extract the middle part</span>
    middlePart = inStringValue.copyFrom_to(6, indexOfLastSeparator-1);
 
    <span style="color:#007F00">// write to the output pin</span>
    outString.value(middlePart);
 }

<!-- There is one possible pitfall, when using JavaScript:
JavaScript array-indexing is 0-based, whereas Smalltalk uses 1-based indices. This applies to all standard JavaScript functions (of which "indexOf" is one). However, when Smalltalk functions are called from JavaScript (as is the case with "copyFrom_to" above), we have to adjust the index.-->


You should always provide a little test and demo of your elementary actions in the Test/Demo page.
There, place at least one instance of the block as a step, give it its required inputs and execute it there.
For example:

[[Bild: string_example_elementaryBlock_test.png]]