Special Purpose Functions

t_closure _self

Unless redefined, the name _self always refers to the model in which it textually occurs. In effect, every model imports itself under this name, prior to the first import clause that appears explicitly in the SDL program text.

t_text
_model_name(t_closure m)

The value m must be a model; that is, a closure defined by importing an immutable file from the Vesta repository. _model_name returns a text value that gives one name for m within the repository. If a model with identical contents in an identical directory is present at several locations in the repository, the name returned may be that of any of these locations, not necessarily the one that was actually imported in the current evaluation.

t_text
_fingerprint(t_value v)

The _fingerprint primitive returns a text representation of the given value's fingerprint, a 128-bit internal identifier for the value. Fingerprints are chosen so that with very high probability, two different values will always have different fingerprints. A given value may have different fingerprints in different evaluations or when computed at different points in the same evaluation, but the implementation tries to avoid this when practical.

Specifically, a source with a particular absolute name in the Vesta repository always has the same fingerprint, while two sources with different names but with the same value will have the same fingerprint if they were fingerprinted by content when inserted into the repository. See the documentation of the vadvance program for details on when sources are fingerprinted by name and when by content. A derived value returned by any Vesta primitive other than _run_tool has a fingerprint that depends deterministically on the fingerprints of its arguments. Derived values returned by _run_tool have either arbitrary unique fingerprints or deterministic content-based fingerprints; see Section A.3.4.8 for details.

These properties make fingerprints useful as version stamps for Vesta evaluations, sometimes more useful than _model_name. If m1, m2 are models with identical contents that reside in identical directories, then _fingerprint(m1) = _fingerprint(m2) will often be true even when _model_name(m1) != _model_name(m2).