A YamlChan is a specialised form of Channel which supports YAML I/O operations. Writing an Object to a YamlChan (using AST_WRITE) will, if the Object is suitable, generate an YAML description of that Object, and reading from a YamlChan will create a new Object from its YAML description.
Normally, when you use a YamlChan, you should provide
" routines which
connect it to an external data store by reading and writing the resulting text. These routines should
perform any conversions needed between external character encodings and the internal ASCII
encoding. If no such routines are supplied, a Channel will read from standard input and write to
If the null routine AST_NULL is suppied as the SOURCE value, and no value has been set for the SourceFile attribute, the YamlChan will read from standard input instead.
If the null routine AST_NULL is suppied as the SINK value, and no value has been set for the SinkFile attribute, the YamlChan will write to standard output instead.
The names of the routines supplied for the SOURCE and SINK arguments should appear in EXTERNAL statements in the Fortran routine which invokes AST_YAMLCHAN. However, this is not generally necessary for the null routine AST_NULL (so long as the AST_PAR include file has been used).
If the external data source or sink uses a character encoding other than ASCII, the supplied source and sink functions should translate between the external character encoding and the internal ASCII encoding used by AST.
A null Object pointer (AST__NULL) will be returned if this function is invoked with the AST error status set, or if it should fail for any reason.
Note that the null routine AST_NULL (one underscore) is different to AST__NULL (two underscores), which is the null Object pointer.