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The SKIRT project
advanced radiative transfer for astrophysics
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The SKIRT project
advanced radiative transfer for astrophysics
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#include <BooleanExpression.hpp>
Static Public Member Functions | |
| static bool | evaluateBoolean (string expression, std::function< bool(string)> isIdentifierTrue) |
| static string | evaluateConditionalValue (string expression, std::function< bool(string)> isIdentifierTrue) |
The BooleanExpression class allows evaluating a Boolean expression or a conditional value expression given the Boolean value for each of the identifiers in the expression.
An identifier in an expression consists of an arbitrary sequence of (upper- and lowercase) letters and digits, starting with a letter. The latter requirement is not verified by the current implementation, but is imposed to allow possible future extensions to recognize, for example, integer constants. The caller is expected to provide a call-back function to determine the Boolean value for each identifier in the expression.
Boolean expression
In a Boolean expression, identifiers are combined with the unary negation operator "!", the binary OR operator |, the binary AND operator &, and (balanced) parenthesis to determine the ordering of operations. In the absence of parenthesis, the negation operator has the highest precedence; otherwise operations are executed from left to right. When mixing OR and AND operators it is therefore highly recommended to use parenthesis.
Boolean expressions are not allowed to contain whitespace. By convention, an empty Boolean expression has a value of true.
Conditional value expression
The syntax of a conditional value expression can be illustrated as follows:
<Boolean-expression1>:<value1>; ... ;[<Boolean-expressionN>:]<valueN>
In other words, there is a sequence of one or more condition-value pairs separated by a semicolon, while the condition and the value are separated by a colon. The pairs in the conditional value expression are considered from left to right. When the condition for a pair evaluates to true (using the Boolean expression rules described above), the corresponding value represents the value of the complete expression and further evaluation is terminated. If none of the conditions evaluate to true, the value of the expression is the empty string.
The condition in a pair (and the colon separating it from the value) may be omitted. In this case, the condition defaults to true. This makes sense only for the last (or only) pair in the sequence, because any remaining pairs will never be considered.
The value of a conditional value expression is always a string, which may be empty. Conditional value expressions are not allowed to contain whitespace except as part of the value. The overall expression syntax disallows a value to contain colons and semicolons. This is no problem for values that represent a number or a type name, and even for other types of values it is most likely not a significant limitation.
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This function evaluates the specified string as a Boolean expression in the format decribed in the class header, and returns the result. When evaluating the expression, each identifier is replaced by the value returned by the specified callback function. The function throws an error if the expression string does not conform to the syntax of a Boolean expression.
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This function evaluates the specified string as a conditional value expression in the format decribed in the class header, and returns the result. When evaluating the expression, each identifier is replaced by the value returned by the specified callback function. The function throws an error if the expression string does not conform to the syntax of a conditional value expression.