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SPARK 0.8

SPARK 0.8. David Morley, Nov 2005. Core Data Types. Includes values most often used by SPARK Primitive Integer, e.g. 1 Float, e.g., 1.0 String, e.g., “one” Symbol, e.g., one Variable designator, e.g., $var (new in 0.8) Compound Structure, e.g., (foo 1 2 3) - has functor symbol foo

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SPARK 0.8

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  1. SPARK 0.8 David Morley, Nov 2005

  2. Core Data Types • Includes values most often used by SPARK • Primitive • Integer, e.g. 1 • Float, e.g., 1.0 • String, e.g., “one” • Symbol, e.g., one • Variable designator, e.g., $var (new in 0.8) • Compound • Structure, e.g., (foo 1 2 3) - has functor symbol foo • List, e.g., [1 2 3]

  3. SPARK-L Source • Represented by core data values (cf. Lisp, Prolog) • SPARKL source to generate a value usually different from the value: • (+ 1 2) ⇒ 3, (- 4 1) ⇒ 3, 3 ⇒ 3 • [(+ 1 2) 3] ⇒[3 3] • (@ “one”) ⇒ one • (@@ “foo” 1 2 3) ⇒ (foo 1 2 3) • (@@ “bar” (+ 1 1) (+ 2 2)) ⇒(bar 2 4)

  4. Backquote and comma • Used for easy construction of basic values (cf. Lisp) • Backquote ` prevents evaluation • `one ⇒ one • `(foo 1 2 3) ⇒(foo 1 2 3) • Comma , performs evaluation within backquote • `(bar ,(+ 1 1) ,(+ 2 2)) ⇒(bar 2 4)

  5. File • Contains • Package statement • Identifier declarations • Import statements • Export statements • Require statements • Facts to be loaded • Every identifier (unquoted symbol or functor) used in the file must have a visible declaration. • Declarations in the file are visible • Imported declarations are visible • Any declaration visible to the package is visible

  6. Package • A Package is • A “bucket” that accumulates declarations, imports, exports from files • A means of communicating declarations between files • Files can use identifiers from their package • Files import identifiers from other packages into their package • Files export identifiers from their package • Unlike old concept of module: • Not a fixed set of files • New files can add identifiers to a package

  7. Specifying the Package of a File • “package: P” • For backward compatibility: • “module: P” = “package: P” • If no package statement, package = filename

  8. File-Local Names • Not all declarations are shared with the package • Identifiers starting with underscore are only visible in the file • _foo, _LocalPredicate, _Procedure1 • It is conceivable (but no syntax exists) to import an identifier foo as a different identifer _foo. That import would not be visible to the package.

  9. Identifiers and Symbols • Identifers are local names • interpreted with respect to a file • To distinguish identifiers in different files we associate a symbol with every identifier: For identifiers declared in file F in package P: • Id maps to symbol P.Id • _Id maps to symbol F._Id • When an identifier declared as a functor appears instead as a symbol, it evaluates to the corresponding symbol: • Given {defpredicate (Id $x)} {defpredicate (_Id $y)} • Id ⇒ P.Id, _Id ⇒ F._Id (cf. `Id ⇒ Id and `_Id ⇒ _Id) • Useful for passing as an argument to applyfun, etc. • Less need for “(qent Id)”

  10. Importing from a package • Q. When you say “importfrom: P” which files do you get declarations from? • Ans. All files in the transitive closure of the “requires” relation that are in package P. • F requires F’ if F contains requires: F’ • F requires P if F contains importfrom: P … • F requires P if F is in package P • P requires F if F has the same name as P

  11. Usage • SPARKL source expressions can be used in different ways • Each way designated by a usage character: + evaluate term [set: $x (+ 1 2)] - match term (= [$x $y] [1 2]) s solve predicate [context: (P $x) ] u update predicate [conclude: (P 7) ] r retract predicate [retract: (P 4) ] … • SPARKL source processing assigns a usage to each expression in source

  12. Mode declaration for a functor • Specifies argument usages • Used for static mode checking of action/predicate usages before file is loaded • Prefix inputs with “+”, outputs with “-” • {defaction (act +$x $y -$z)} In any use of this action: • $x must be evaluable (I.e., is an input) • $y need only be matchable (I.e., can be an output) • $z must not be evaluable (I.e, must be output)

  13. Formal parameters • Richer formal parameters for: • defprocedure cues • task closure parameters • pred closure parameters • Parameter may be one of: • +X - at start, match X to the actual parameter value • -X - at end, match actual parameter to the value of X • $x - at start, constrain $x to match actual parameter • Examples: • +[$x $y] - match input parameter to [$x $y] • Less need for Ground

  14. Accessing Core Valuesfrom Python • See Python module spark.internal.parse.basicvalues • Core data types are called: String, Float, Integer, Symbol, Variable, Structure, List • Symbol(“foo”), List((1,2,3)), isinstance(x,List) • Structure args/List elements access: • myStruct[0], len(myStrict), myList[1:2] • Structure functor access: • myStruct.functor • Symbol name access: • mySym.name or str(mySym) • Construct Structure: • Structure(functorSym, argsSequence) or functorSym.structure(arg0, arg1, …)

  15. Random Bits • “precondition: X” is now optional • No distinction between task modifiers and basic tasks • [context: X do: Y] is a special case of using […] for sequential composition (technically contiguous: rather than seq: )

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