Clingo treats operations that were assumed to be “invalid” not as
processing errors but as operations returning an empty set.
This changes how formulas have to be evaluated. This commit implements
an explicit function for retrieving the return type of an expression,
that is, both the domain of the result as well as whether it’s an empty,
unit, or general set with multiple values.
The “general” domain wasn’t really about general variables, but meant as
a distinction from integer variables. For this reason, this commit
renames the “general” domain to “noninteger.”
Checking whether terms are arithmetic will be used not just in integer
variable detection but also in simplifying formulas with integer
variables. For this purpose, the arithmetic check is moved to a commonly
accessible header file.
This moves the commonly enum classes EvaluationResult, OperationResult,
and Tristate to the Utils header file to avoid code duplication.
Additionally, the SimplificationResult class is replaced by the
semantically similar OperationResult.
This adds a new syntax for declaring functions integer:
#external integer(<function name>(<arity)).
If a function is declared integer, it may enable some variables to be
detected as integer as well.
For clarity, this moves the Domain enum class to a separate header,
because it’s not just variable-specific but also applicable to
functions, for example.
This adds initial support for detecting integer variables in formulas.
The scope is somewhat limited in that variables matching predicate
parameters with known integer type aren’t propagated to be integer as
well yet. Also, the use of constants and functions prevents variables
from being detected as integer, because they have to be assumed to be
externally defined in such a way that they evaluate to general values
and not necessarily integers.
The Tristate class (representing truth values that are either true,
false, or unknown) is used at multiple ends. This moves it to a separate
header for reusing it properly.
This refactoring separates predicates from their declarations. The
purpose of this is to avoid duplicating properties specific to the
predicate declaration and not its occurrences in the program.
With this change, the domain of variable declarations can be specified.
While the default is the general domain of all precomputed value, this
adds support for integer variables, for which advanced simplification
rules apply.
The unary modulus operation does not require extra parentheses to be
printed in cases like “|X + Y|”. This adds a new option to the printing
routine to omit parentheses in cases where the parent expression already
defines a parenthesis-like scope (currently only with unary operations).
Because of a bug in the Clingo API, the exponentation operator was not
properly exposed to anthem. This updates Clingo to a version with a
fixed API and adds proper support for exponentation within anthem along
with a matching unit test.
This adds support for declaring predicates as placeholders through the
“#external” directive in the input language of clingo.
Placeholders are not subject to completion. This prevents predicates
that represent instance-specific facts from being assumed as universally
false by default negation when translating an encoding.
This stretches clingo’s usual syntax a bit to make the implementation
lightweight. In order to declare a predicate with a specific arity as a
placeholder, the following statement needs to be added to the program:
#external <predicate name>(<arity>).
Multiple unit tests cover cases where placeholders are used or not as
well as a more complex graph coloring example.
With C++17, optionals, an experimental language feature, were moved to
the “std” namespace. This makes C++17 mandatory and drops the now
obsolete “experimental” namespace.
Patrick Lühne