System functions (Quad functions)

 
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The built-in System functions extend the power of APLX by providing easy-to-use cross-platform tools for achieving many common and more complex tasks.

In general, the same system functions are supported by all versions of APLX, so that code written using them will run under Windows, Macintosh and Linux. However you should note that APL interpreters from other vendors may implement a different set of functions which is often much less rich.

There are too many system functions to cover in detail here, but here are just a few...

System functions for manipulating data

There are a number of system functions that manipulate data, including:

For reshaping vectors as matrices (and visa versa) a system function, ⎕BOX is available:

      ⎕BOX 'COGS WHEELS SPRINGS'
COGS
WHEELS
SPRINGS

and for deleting spaces from character data, there's another system variable, ⎕DBR (Delimited Blank Removal):

      ⎕DBR '       WIDE     OPEN           SPACES'
WIDE OPEN SPACES

Another function is ⎕SS (String Search and Replace). In this example, all occurrences of the characters ARE in a text variable are replaced by ARE NOT:

      MANIFESTO ← 'ALL ANIMALS ARE EQUAL'
      ⎕SS (MANIFESTO; 'ARE'; 'ARE NOT')
ALL ANIMALS ARE NOT EQUAL.

⎕SS is extremely powerful. It can also be used to perform regular expression searches.

There are further details and examples of these three system functions and others in the APLX Language Manual.

System functions for reading and writing files

APLX includes a large number of functions for reading and writing files.

Examples of native file functions

1. To read an existing text file into an APL variable:

      'C:\Documents\MyFile.txt' ⎕NTIE 1
      TEXT ← ⎕NREAD 1 4
      ⎕NUNTIE 1

The whole of the specified file is read into the APL variable TEXT with characters converted to APL's internal representation.

2. To create a new text file containing the text 'Hello new file':

      'C:\Documents\MyNewFile.txt' ⎕NCREATE 1
      'Hello new file' ⎕NWRITE 1 4
      ⎕NUNTIE 1

3. To write out a table of data as a web page:

      SalesData ⎕EXPORT 'C:\Documents\SalesData.html' 'html'

4. To read a table of spreadsheet data in Comma-Separated Variable (CSV) format:

      data ← ⎕IMPORT 'C:\Documents\SpreadsheetData.csv' 'csv'

Some more useful system functions

For full details of all system functions and many more examples, see the APLX Language Manual.

Examples

1. To display a chart of sales data:

      SALES ← ?3 12⍴20
      ⎕CHART SALES

Here we generate some random sales data and display it in chart form in a new window:

2. To create a new window containing an Edit field.

      DEMO ← '⎕' ⎕NEW 'Dialog' ⋄ DEMO.title ← 'Edit Example'
      DEMO.myEdit.New 'Edit' ⋄ DEMO.myEdit.where ← 2 1
      DEMO.myEdit.text ← 'Some sample text'

This will create the following window (the appearance will be different if you try this on a Macintosh or Linux version of APLX):

3. To issue a Windows command to list the contents of a folder:

      ⎕HOST 'CMD /C dir'
Volume in drive C has no label.
Volume Serial Number is 07D0-0B11
     Directory of C:\aplx\ws
20/06/2001  19:13       [DIR]          .
20/06/2001  19:13       [DIR]          ..
05/09/2001  16:43               17,792 JIM.aws
05/09/2001  17:06                  574 EXPLORE.atf
30/07/2001  19:49               17,828 QNA.aws
          3 File(s)         39,313 bytes
          2 Dir(s)  14,797,176,832 bytes free

5. Here we use SQL to connect to a database and read a table of data into the APL variable employeeData, check how many results were returned, and then display the first five:

      1 ⎕SQL 'connect' 'aplxodbc' 'DSN=BigCorpDB;PWD=xx;UID=root;'
0 0 0 0
      1 ⎕SQL 'do' 'use bigcorp'
0 0 0 0
      fields ← 'FIRSTNAME,LASTNAME,SEX,EMAIL,EMPLOYEENUMBER,DEPARTMENT'
      (rc errmsg employeeData) ← 1 ⎕SQL 'do' 'select',fields,'from employeedata'
      ⍴employeeData
350 6
      5 6↑employeeData
 Bert     Brown      M Bert.Brown@bigcorp.com      1 C
 Claude   Ptolemy    M Claude.Ptolemy@bigcorp.com  2 B
 Zak      Smith      M Zak.Smith@bigcorp.com       4 E
 Sian     Jones      F Sian.Jones@bigcorp.com      5 C
 Eric     Smallhorse M Eric.Smallhorse@bigcorp.com 6 C