Return values

get-actions:

you should return a string or an int. AHTS doesn't cache any values, so <if @x@ eq @x@> will call your DataSource twice. You should return the same value both times.

prepare-actions:

if you know the number of rows, you should return it. Returning this value makes the special variable identifier:rowcount available. This value won't be available, if you return None.

next-actions:

you must return true if you have more data to follow, and false if you haven't got any more data. (true or false is meant in the Python-sense, so false can be an empty list, or 0, or '')

done-actions:

you shouldn't return anything at all.

Types

AHTS knows the following types: integers and strings. When printing an identifier, it will be coerced to a string. When evaluating comparisons, AHTS will try to coerce both operands to integers, and compare them. If this fails they will be compared as strings.

Exceptions

Exceptions raised by AHTS:

ahts.ScannerError:

raised by the Scanner, when it finds itself in an inconsistent state. This can't happen™.

ahts.SyntaxError:

called when the parser reaches an ambiguous situation. The expception-string provides the file, line number and column.

ahts.RuntimeError:

called at runtime, whenever the writer encounters an error. Possible causes:

1. Bugs in the code
2. <if @identifier@ (odd | even) > where identifier is not coercable to an integer.

This exception does not (yet) provide the filename, number, etc.

Exceptions you should raise:

ahts.NotDefinedError:

Your DataSource should raise this exceptions every time you encounter a variable (identifier) you can't handle. AHTS will catch this exception in two specific cases:

• When handling an <if @identifier@ defined>-statement.
• When handling an <if @identifier@ nil>-statement.