Message 03 Numeric Expressions

The message type ExprComposite represents an expression in prefix notation. The message is an ordered list of operators and operands, each represented using the ExprBase message type.

# A message used to represent a numerical expression; composite type (2/2)
# stores an array of ExprBase as prefix notation

# components
ExprBase[] tokens

The ExprBase message type looks like this:

# A message used to represent a numerical expression; base types (1/2)

# expression types
uint8 CONSTANT = 0
uint8 FUNCTION = 1
uint8 OPERATOR = 2
uint8 SPECIAL  = 3

# operators
uint8 ADD    = 0
uint8 SUB    = 1
uint8 MUL    = 2
uint8 DIV    = 3
uint8 UMINUS = 4

# special types
uint8 HASHT      = 0
uint8 TOTAL_TIME = 1
uint8 DURATION   = 2

# expression base type
uint8 expr_type

# constant value
float64 constant

# function
rosplan_knowledge_msgs/DomainFormula function

# operator
uint8 op

# special
uint8 special_type

For example, the consider the following ungrounded numeric expression:
(* ?duration (+ (energy ?r) 10))

It is described by the ExprComposite message in the following way:

tokens:
- expr_type: 2
  op: 2
- expr_type: 3
  special_type: 2
- expr_type: 2
  special_type: 0
- expr_type: 1
  function:
    name: energy
    typed_parameters: 
      - 
        key: r
        value: robot
- expr_type: 0
  constant: 10

in which the tokens are a prefix array of ExprBase messages:
[ *, ?duration, +, (energy ?r), 10 ]

ROSPlan

Message 03 Numeric Expressions