Clause Struct Reference

Holds a fragment of a constraint expression. More...

#include <Clause.h>

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Public Member Functions

bool boolean_clause ()
 Return true if the clause returns a boolean value.
 Clause ()
 Clause (btp_func func, rvalue_list *rv)
 Clause (bool_func func, rvalue_list *rv)
 Clause (const int oper, rvalue *a1, rvalue_list *rv)
bool OK ()
 Checks the "representation invariant" of a clause.
bool value (const string &dataset, DDS &dds, BaseType **value)
 Evaluate a clause that returns a value via a BaseType pointer. This method must only be evaluated for clauses with relational expressions or boolean functions.
bool value (const string &dataset, DDS &dds)
 Evaluate a clause which returns a boolean value This method must only be evaluated for clauses with relational expressions or boolean functions.
bool value_clause ()
 Return true if the clause returns a value in a BaseType pointer.
virtual ~Clause ()

Detailed Description

The selection part of a a DAP constraint expression may contain one or more clauses, separated by ampersands (&). This is modeled in the DDS class structure as a singly-linked list of Clause objects. In addition, a constraint expression may be a single function call, also represented in the DDS using an instance of Clause.

Each clause object can contain a representation of one of three possible forms:

  1. A relational clause, where an operator tests the relation between two operands. This kind of clause evaluates to a boolean value. For example: a > b.

  2. A boolean function, where some function operates on arguments in the clause to return a boolean value. For example, consider a scalar A and a list L. The clause find(A,L) might return TRUE if A is a member of L (if the find() function is defined).

  3. A clause that returns a pointer to a DAP BaseType value. This is a clause that evaluates to some data value (be it scalar or vector). For example, sig0() might be included in the constraint expression parser to calculate density from pressure, temperature, and salinity. In this case, sig0(p,t,s) would be a clause that evaluates to a data value.

This might be a bit confusing; in the first, and by far more common, form of constraint expressions (CEs) only the first two types of clauses may appear. In the second form of the CE only the last type of clause may occur. The Clause class, however, can store them all.

The Clause object holds the constraint expression after it has been parsed. The parser renders the relational operator into an integer, and the functions into pointers.

See also:
DDS::parse_constraint

Definition at line 87 of file Clause.h.


Constructor & Destructor Documentation

Clause::Clause ( const int  oper,
rvalue a1,
rvalue_list rv 
)

Definition at line 48 of file Clause.cc.

References OK().

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Clause::Clause ( bool_func  func,
rvalue_list rv 
)

Definition at line 54 of file Clause.cc.

References OK().

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Clause::Clause ( btp_func  func,
rvalue_list rv 
)

Definition at line 65 of file Clause.cc.

References OK().

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Clause::Clause (  ) 

Definition at line 76 of file Clause.cc.

Clause::~Clause (  )  [virtual]

Definition at line 85 of file Clause.cc.


Member Function Documentation

bool Clause::boolean_clause (  ) 

Definition at line 122 of file Clause.cc.

References OK().

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bool Clause::OK (  ) 

Definition at line 101 of file Clause.cc.

Referenced by boolean_clause(), Clause(), value(), and value_clause().

bool Clause::value ( const string &  dataset,
DDS dds,
BaseType **  value 
)

Parameters:
dataset This is passed to the function.
dds Use variables from this DDS when evaluating the expression
value A value-result parameter
Returns:
True if the the BaseType pointer is not null, false otherwise.
Exceptions:
InternalErr if called for a clause that returns a boolean value. Not that this method itself does return a boolean value.

Definition at line 197 of file Clause.cc.

References build_btp_args(), OK(), and value().

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bool Clause::value ( const string &  dataset,
DDS dds 
)

Parameters:
dataset This is passed to the rvalue::bvalue() method.
dds Use variables from this DDS when evaluating the expression
Returns:
True if the clause is true, false otherwise.
Exceptions:
InternalErr if called for a clause that returns a BaseType pointer.

Definition at line 148 of file Clause.cc.

References build_btp_args(), rvalue::bvalue(), OK(), and BaseType::ops().

Referenced by ConstraintEvaluator::eval_function(), and value().

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bool Clause::value_clause (  ) 

Definition at line 131 of file Clause.cc.

References OK().

Referenced by ConstraintEvaluator::functional_expression().

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The documentation for this struct was generated from the following files:
Generated on Wed Jun 27 12:57:36 2007 for libdap++ by  doxygen 1.4.7