Rule based scripts

Introduction

This plug-in implements a language that is a mixture of a rule-based and a sequential based language. The idea is that a number of situations need permanent - or semi permanent - monitoring to get a good situation awareness, and at the same time accept that a large number of the robot tasks are better described by a sequential language.

This implementation attempts to cover this gab.

Language

An example rule definition file could look like this:

<?xml version="1.0" ?>
<rule name="CrossRoad">
   <init>
       odoPose.tripB = 0
       nearRoad = false // define local variable
       <rule name="maxOdoDist" if="odoPose.tripB > 250">
           // this is a rule to moditor distance traveled since trip-counter were reset
           print("Driven too far on odo " odoPose.tripB "m") // print message
           break CrossRoad // failed to cross road - could trigger a relocalization
       </rule>
       <rule name="closeToRoad" if="hypot(utmPose.poseY - 6174307, utmPose.poseX - 707873) < 15" >
           // this is a rule that monitors the distance to an UTM point
           print("Cose to road slowing down) // print message
           smr.speed=0.5  // set the desired maximum speed in mrc interface module
           nearRoad = true  // set flag
           disable  // disable this rule
       </rule>
       <rule name="turn">
           <parameter angle="pi" dist=1.0/>
           // this is a plan 
           <commands to="smr.send">
             # construct commands to MRC using the smr.send command
             'drive @v ' smr.speed ' : ($drivendist > ' dist ')'
             'turn ' angle
             'drive : ($drivendist > ' dist ')'
           </commands>
       </rule>
   </init>
   print("started")
   roaddrive.right(0.75) : nearRoad // follow road 75cm from edge until near road
   // more stuff missing here to detect traffic etc.
   ...
   turn() // turn back - using a call to a plan
   success=true
   <post>
       print("finsihed crossRoad - success=" success)
   </post>
</rule>

A number of these rules can be active simultaneously, and can be total independent. I.e.one can control the robot arm while another controls the navigation.

Language keywords

Rule

A rule statement must be formed as a XML block structure, as shown below

<rule name="foo" run="true">
   statements
</rule>
<rule name="bar" if="rule_condition">
   statements
</rule>

Rules comes in two flavors, rules and inactive rules. A (active) rule must have a rule condition in an if="" attribute like the plan "bar" above. A rule without the if="" attribute is inactive until called, or made active by a "enable" statement. If it is a top-level rule, then it can be made active when loaded by a run="true" attribute. The run="true" attribute will make it run once

The rule may have a description, like

<rule name="foo" run="true">
   <description>
   This is the descriptive text of "foo", it may have any length, and is intended as an on-line available description of the rule.
   It is optional and recommended only for top-level rules.
   </description>
   statements
</rule>

Rule as a function

A rule may have optional parameters, that can be used if the rule is called from another rules (as a procedure or function, that do not return a value), i.e.:

<rule name="foo">
   <parameters x="0.28" y="0" th="pi" b="'empty'"/>
   statements
</rule>
<rule name="bar">
   foo()
   foo(1.5, 0.0, pi/2, "pose")
</rule>

Here the rule "bar" uses the "foo" rule as function, first by using the default values, and after this with new values replacing the default values in "foo". The parameters in "foo" works like local variables in the "foo" plan. The last parameter is a string, that must be initialized to a string constant, here shown as the string empty, this value is in the last call replaced with the string pose. A rule may be called recursively, and each call will have its own set of local variables. There is a limit to the number nested calls.

Local variables

A rule may define local variables and sub-rules, like

<rule name="foo">
   <init>
      x = 88;
      x2 = sqr(x)
      <rule name="bar" if="x < 22")
         print("x is now " x)
      </rule>
   </init>
   statements
</rule>

Here x and x2 are newly established local variables The rule "bar" is active as long as the plan "foo" is active.

String variables are partially implemented, and may be used in some situations, like:

<init>
  b = 5
  aa = 'the value of b is ' b 'meters'
</init>

This should result in the string "the value of b is 5meters" to be printed on the server console.

A variable may have more than one value, i.e.:

<init>
  b[2] = 5      # allocates space for 3 elements
  b[1] = 22.7   # assigns value to second element
  b[0] = 0.5    # assigns value to first element
  a = b         # copies all elements in b to a
  c = atan2(a[2] - 3.3, a[1] - 1) 
</init>

Some calls may support parameters that take such arrays, i.e. coordinate conversion

All non-string variables are implemented as doubles.

Init and Post blocks

A rule may have an init block, to define local varaibles and sub-rules and to do some initial processing. The init block is executed once only, when the rule is first activated (the rule condition is fulfilled or the rule is a top level rule activated by a run=true attribute).

If the rule is called from another rule, then the init-block is run at the start of the call, every time such a call is performed.

<rule name="foo">
   <init>
      global.fooCnt = 0
      global.fooActive = 0    
   </init>
   global.fooActive = true    
   main statements
   <post>
      global.fooCnt = global.fooCnt + 1
      global.fooActive = false    
   </post>
</rule>

A rule may further have a Post block. The post block is executed as the last set of statements even if the rule is disabled by another rule or the rule has a break in its main statements.

Global variables

A rule may create and use global variables, e.g.

<rule name="foo" if="utmpose.posey < 1000">
   <init>
      global.equatorWarning = false;
   </init>
   global.equatorWarning = true;
</rule>

This rule is triggered by the Northing in the utmPose module, "utmpose.posey" is here a global variable. The rule defined a new global variable "global.equatorWarning", this must start with the keyword "global", and is then available for all other rules (in all scopes).

Strings

Strings may be used as parameters and can be concatenated by substrings or values, e.g.

print("The value of a is " a "meter")

is evaluated to (if a has the value 1.47)

print("The value of a is 1.47 meter")

A string parameter must start with a quote (") or apostrophe ('), if the first part of the string should be a number, then start with an empty string.

A string may hold another string, but the quotes (") or apostrophes (') must come in matched pairs, e.g.

print('an eval "$odox" may return ' 0.0 ", but an "a" may be a value")

will evaluate as

print('an eval "$odox" may return 0, but an 1.47 may be a value')

Numbers will be inserted as a string using the %g 'printf(...)' format specifier

Enable/Disable

This will make a rule active - if not already, or stop or prohibit a plan from getting active, e.g.

enable foo

Will make the rule "foo" active, that is start running the code as if it was a rule. If there is a rule condition, then the code will not run until the condition is satisfied. if the rule has no rule condition, it will run once only.

If the rule is active already, either it is an active rule or the plan is waiting at a control statement, the statement will have no effect.

The disable command:

disable foo

Will disable the plan "foo", if the plan is a rule, then the rule condition will no longer be evaluated. If the rule is waiting at a control statement, then this will be interrupted, and any post-lines will be executed, before the rule is disabled. If the rule is not a rule and is not waiting at a control statement, then the statement will have no effect. A called rule will not be affected by the 'disable rulename' statement

A rule can disable itself with the statement:

disable

(a rule can not enable itself)

Loop statements

Loop statements resembles the C syntax, but is line oriented. A sample loop could look like this

<rule name="foo">
  <init>
     cnt = 1
  </init>
  while (cnt < 70)
  <block>
     cnt = cnt * 2
     print("Loop cnt is now " cnt)
     if (cnt >= 16)
       break
  </block>
  for (i = 0; i < 5; i = i + 1)
    print("For loop, i=" i);
</rule>

This defines the local variable "cnt" and later implicitly the variable "i". The first while loop doubles cnt until it reaches 16, where the break terminates the loop. The for loop defines a local variable "i", which after the first use is available as a local variable.

Break statement

Breaks the first loop (see loop statement), or breaks a rule or a named rule, as in

<rule name="foo">
  <init>
     ...
     <rule name="exception" if="global.emergency">
        break foo
     </rule>
  </init>
  ...
  if (not defined(global.emergency))
    break
  control statement, e.g.
  wait() : false
  ...
  <post>
     stopRobot()
  </post>
</rule>

Here the break in the rule exception has a break foo statement, that will break the foo rule (and run the post block). The break in the main statements of the foo rule has no rule name, and will thus break the current rule (if not inside a loop statement - if so the rule can be stopped by the named version of the break command.

If statement

Nested if and if-else statements are supported in up to 10 levels

The if condition is evaluated as either false or true. False is any value in the interval [-0.5 to 0.5], all other values are regarded as true. Boolean operators evaluate to 0 (false) or 1 (true).

<rule name="foo" if="true">
  <init>
    a = false
    b = 1
    c = 2
  </init>
  if (c == 0)
    a = true
  else
  if (not a)
  <block>
    a = true
    if (b == 1)
      b = 77
    else
      b = b + 1
    c = 0
  </block>
</rule>

Case statement

A case statement has the following syntax

<rule name="foo" if="true">
  <init>
    a = 3
  </init>
  switch (a + global.a)
  <block>
     case 3
       print("Global.a has a low value")
     case 4,5,-6, -7 ,8  # a remark
       print("a range of values, a is " a " and global A is " global.a)
       global.a = 9
       print("a set to 9")
     case 9  # no statement is executed if switch value is 9
     default
       print("default statement if outside range")
  </block>
</rule>

Case statements may be nested.

Function calls

Three call types are supported:

• call to another rule - as described above
• call to a method in another plugin - e.g.:

smr.send('followline "bl" : ($crossingblackline)')

• call to a standard function, e.g:

a = atan2(4,3)
d = sin(pi/4)

Standard functions

The following values and functions are implemented

false = 0.0
true = 1.0
pi = M_PI

limitToPi(d)
sin(d)
cos(d)
hypot(dd)
acos(d)
asin(d)
tan(d)
atan(d)
atan2(dd)
sqrt(d)
sqr(d)
abs(d)
max(dd)
min(dd)
defined(s)
now()
poseToMap(dddddd)
mapToPose(dddddd)

The function parameters are of type "d" for double or "dd" for two doubles (comma separated). The defined function uses a string as parameter, e.g. defined("false") returns true. Angle values are in radians.

See on-line help

>> var math

for any other implemented standard functions (and function description)

Control statement

A control statement is constructed of a call to a plug-in method and a condition for continuation, like

smr.event() : abs(odoPose.vel) < 0.05

The rule will stay at this line until either the "smr.event()" returns 2, or the expression after the ":" evaluates to true.

The control statement call must accept one "d" parameter more than shown in the control statement, i.e. the smr.event(d) call must be defined with a "d" parameter. This extra parameter is called an iteration parameter. When the rule gets to this line the iteration parameter is zero, the subsequent times the rule is evaluated, the iteration parameter is incremented by one. This is done to allow the plug-in method to initialize the control, when the parameter is 0, and just test for completion at the subsequent calls. If the control statement is interrupted by a break or disable statement, then the control function is called with the iteration parameter set to -1.

If the control calls are used outside a control statement the iteration parameter must be specified explicitly, e.g.

 smr.event(0)

will initialize a user event on the MRC command queue, and

 if (smr.event(1) == 2)

will evaluate to true when the user event is executed by the MRC. NB! the smr.event(1) itself will return true if the function is defined (i.e. plugin loaded) and false if it is not.

Language definition

The language definition is:

Rules

ruleBlock ::= ruleOpenTag ruleBody ruleCloseTag

ruleOpenTag ::= '<rule' 'name=' ruleName [runAttribute] [ruleCondition] [evaluateOrder]'>\n'

ruleName ::= '"' symbol '"'

runAttribute ::= 'run' ['="true"' | '="false"']

ruleCondition ::= 'if="' expression '"' (this expression may be split into more lines)

evaluateOrder ::= 'order="' number '"' (number in range 1..100, default is 50, lower number is run first)

ruleCloseTag ::= '</rule>\n'

ruleBody ::= [parameters] [description] [ruleInitBlock] ruleMainBlock [rulePostBlock]

parameters ::= '<parameters ' [symbol '="' [paramDefaultValue] '"']* '/>\n'

paramDefaultValue ::= constantNumericValue | constantStringValue

description ::= '<description>\n' xmlText '</description>\n'

xmlText ::= any 7-bit characters except '\0', '&' and '<', the last two should be coded as & and <

ruleInitBlock ::= '<init>\n' [declarationStatement]* '</init>\n'

declarationStatement ::= ruleBlock | executableStatement

ruleMainBlock ::= [statement]*

rulePostBlock ::= '<post>\n' [statement]* '</post>\n'

constantStringValue ::= ' [xmlText] ' | " [xmlText "

Statements

statement ::= executableStatement | controlStatement

executableStatement ::= assignment | procedureCall | blockStatement | breakStatement | enableStatement | ifStatement | loopStatement | caseStatement | emptyStatement

controlStatement ::= proceureCall ':' expression [remark] '\n'

assignment ::= [symbol.]* symbol '=' expression [remark] '\n'

procedureCall ::= [symbol.]* symbol '(' [expression [',' expression]* ')' [remark] '\n'

blockStatement ::= '<block>\n' [statement]* '</block>\n'

breakStatement ::= ('break' [symbol] | 'continue' ) [remark] '\n'

enableStatement ::= ('enable' | 'disable') [symbol] [remark] '\n'

ifStatement ::= 'if (' expression ')' [remark] '\n' statement [remark] '\n' [elseStatement]

elseStatement ::= 'else' [remark] '\n' statement [remark] '\n'

loopStatement ::= forStatement | whileStatement

forStatement ::= 'for (' assignment ';' expression ';' assignment ')' [remark] '\n' statement [remark] '\n'

whileStatement ::= 'while (' expression ')' [remark] '\n' statement [remark] '\n'

case statement ::= 'switch (' expression ')' [remark] '\n' blockCaseStatement

blockCaseStatement ::= '<block>\n' [caseStatement]* [caseDefaultStatement] '</block>\n'

caseStatement ::= 'case ' int [, int]* [remark] '\n' [statement]*

caseDefaultStatement ::= 'default' [remark] \n [statement]*

emptyStatement ::= [remark] '\n'

remark ::= ('#' | ';' | '//') xmlText except '\n'