NATURAL

From Wikipedia, the free encyclopedia
Jump to: navigation, search

Natural is a fourth-generation programming language from Software AG. It is largely used for building databases output in plain text form, for example.

* Hello World in NATURAL
WRITE 'Hello World!'
END

It has the ESCAPE TOP flow control instruction, which is similar to continue in C, C++, Java and several other languages, except that it also works within subroutines to both return from the routine and then continue the calling statement's processing loop.

Like continue, it avoids large amounts of indentation levels when using nested instruction blocks inside any loop.

Example with ESCAPE TOP:

DEFINE DATA LOCAL
1 I (N3)                                    /* 3 digits without decimals
END-DEFINE
FOR I = 2 TO 100
  IF (I / 2 * 2) = I AND I > 2
    WRITE 'Number' I 'is divisible by 2'
    ESCAPE TOP
  END-IF
  IF (I / 3 * 3) = I AND I > 3
    WRITE 'Number' I 'is divisible by 3'
    ESCAPE TOP
  END-IF
  IF (I / 5 * 5) = I AND I > 5
    WRITE 'Number' I 'is divisible by 5'
    ESCAPE TOP
  END-IF
  IF (I / 7 * 7) = I AND I > 7
    WRITE 'Number' I 'is divisible by 7'
    ESCAPE TOP
  END-IF
  IF (I / 11 * 11) = I AND I > 11
    WRITE 'Number' I 'is divisible by 11'
    ESCAPE TOP
  END-IF
  WRITE 'Number' I 'is prime'
END-FOR
END

The levels of indentation can be automatically adjusted with the STRUCT command in the Natural Editor.

The same example, without ESCAPE TOP:

DEFINE DATA LOCAL
1 I (N3)                                    /* 3 digits without decimals
END-DEFINE
FOR I = 2 TO 100
  IF (I / 2 * 2) = I AND I > 2
    WRITE 'Number' I 'is divisible by 2'
  ELSE
    IF (I / 3 * 3) = I AND I > 3
      WRITE 'Number' I 'is divisible by 3'
    ELSE
      IF (I / 5 * 5) = I AND I > 5
        WRITE 'Number' I 'is divisible by 5'
      ELSE
        IF (I / 7 * 7) = I AND I > 7
          WRITE 'Number' I 'is divisible by 7'
        ELSE
          IF (I / 11 * 11) = I AND I > 11
            WRITE 'Number' I 'is divisible by 11'
          ELSE
            WRITE 'Number' I 'is prime'
          END-IF
        END-IF
      END-IF
    END-IF
  END-IF
END-FOR
END

Another powerful flow control instruction command is the ESCAPE BOTTOM, which is similar to ESCAPE TOP except that it continues the processing from end of the calling statement's processing loop. Example with ESCAPE BOTTOM:

DEFINE DATA LOCAL
1 I (N3)                                    /* 3 digits without decimals
END-DEFINE
FOR I = 2 TO 100
  IF (I / 2 * 2) = I AND I > 2
    WRITE 'Number' I 'is divisible by 2'
    ESCAPE BOTTOM
  END-IF
  IF (I / 3 * 3) = I AND I > 3
    WRITE 'Number' I 'is divisible by 3'
    ESCAPE BOTTOM
  END-IF
  IF (I / 5 * 5) = I AND I > 5
    WRITE 'Number' I 'is divisible by 5'
    ESCAPE BOTTOM
  END-IF
  IF (I / 7 * 7) = I AND I > 7
    WRITE 'Number' I 'is divisible by 7'
    ESCAPE BOTTOM
  END-IF
  IF (I / 11 * 11) = I AND I > 11
    WRITE 'Number' I 'is divisible by 11'
    ESCAPE BOTTOM
  END-IF
  WRITE 'Number' I 'is prime'
END-FOR
END

One trait that sets Natural apart from most other languages is its rich syntax. For example, many languages have a simple switch case statement that can be used to replace nested IF statements pertaining to a single variable; in C-like languages, it is prone to logic errors since it is necessary to BREAK out of the statement programatically. Natural has a much cleaner/richer DECIDE statement which is easier to understand and code. Here is an example:

 DECIDE ON FIRST VALUE MARITAL-STATUS
   VALUE 'M'  DESC := 'Married'
   VALUE 'D'  DESC := 'Divorced'
   VALUE 'W'  DESC := 'Widowed'
   ANY  ONCE-MARRIED := TRUE
   NONE DESC := 'Single'
 END-DECIDE

External links[edit]