Aestiva H2O Web Site

Installation:
  Free Downloads
  The H2O Family
  Install Notes

Programming:
  Prerequisites
  H2O Whitepaper
  Online Manual
  Code Examples
  H2O Free Support

What's H2O?
H2O is programming made for the web.

What's it like?
H2O is English-like. If you know some Perl, VB, ASP, or PhP you'll be immediately productive in H2O. It runs on Linux, Mac, Unix, and Windows.

How do I try it?
Download H2O for free. Get it from hosting providers. Or buy on-line.

Where does H2O come from?
The language was invented by Aestiva. H2O stands for:
   HTML with
   HTML/OS
   Overlays.

Embedded in HTML
H2O code is placed in HTML documents between << and >> characters. There is no requirement for external definition files nor must code be placed in external libraries. For example, writing:

<HTML>
This is my web page.
Today's date is: << DISPLAY TODAY /DISPLAY >>
Yesterday was: << DISPLAY YESTERDAY /DISPLAY >>
The day before that was: << DISPLAY ADDDAYS(TODAY,"-2") /DISPLAY >>

</HTML>

places dates in the page where the macros (the Overlays) are placed.

Overlays can be placed above the <HTML> tag in the document, between the <HTML> and tags or below the </HTML> tag. When placed above the <HTML> tag the Overlay is known as an "Underlay" since it's run before the page is composed. When the macro is placed between the <HTML> and </HTML> the Overlay is called an "Inlay." Overlays placed below the </HTML> are called "On-click Overlays." They can only be run by clicking a link in a web page linked to them. The page below contains an Underlay, an Inlay and an On-click Overlay:

<<IF ISLOGGEDIN="TRUE" THEN GOTO "menu.html" /IF >>
<HTML>
This is my web page.
Today's date is: << DISPLAY TODAY /DISPLAY >><BR>
Type password to enter my site:
<FORM METHOD=POST ACTION=letmein>
<INPUT TYPE=PASSWORD SIZE=15 NAME=mypassword>

<INPUT TYPE=SUBMIT NAME=mybutton VALUE="LOGIN">
</FORM>
</HTML>
<<OVERLAY letmein
    IF mypassword="12345" THEN
      ISLOGGEDIN="TRUE"
      GOTO "menu.html"
    ELSE GOTO PAGE
    /IF

>>

The Underlay is in green. The Inlay is in blue. The On-click Overlay is in red. In this example the user is directed to menu.html if he's already logged in. If not, he is asked to enter a password. When the password is entered it is checked. If okay, the user is sent to menu.html. If not, the user is sent back to the top of the page.

The Overlays, as defined above, give the programmer the ability to modify HTML documents dynamically. Indeed, H2O provides the programmer a complete infrastructure for building web applications.

The DISPLAY Shortcut
In H2O an Overlay containing a single DISPLAY expression /DISPLAY statement may be reduced to only the expression itself. For example, the statement:

   <<DISPLAY TODAY /DISPLAY>>

can be written as:

   <<TODAY>>