java (object oriented) asp rdf (horn clause deduction, semantic web)
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10
Java (Object Oriented)Java (Object Oriented)
ASPASP
RDF (Horn Clause Deduction, RDF (Horn Clause Deduction, Semantic Web)Semantic Web)
RelationRelation
Jython in JavaJython in Java
This CourseThis Course
High LevelHigh LevelLanguagesLanguages
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Lexical and Syntactic Analysis
• Chomsky Grammar Hierarchy
• Lexical Analysis – Tokenizing
• Syntactic Analysis – Parsing
• Hmm Concrete Syntax
• Hmm Abstract Syntax
Programming Languages
Noam Chomsky
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• Regular grammar – used for tokenizing
• Context-free grammar (BNF) – used for parsing
• Context-sensitive grammar – not really used for programming languages
Chomsky Hierarchy
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• Simplest; least powerful
• Equivalent to:– Regular expression (think of perl)– Finite-state automaton
• Right regular grammar: Terminal*,
A and B Nonterminal
A → B
A →
• Example:Integer → 0 Integer | 1 Integer | ... | 9 Integer |
0 | 1 | ... | 9
Regular Grammar
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• Less powerful than context-free grammars
• The following is not a regular language
{ aⁿ bⁿ | n ≥ 1 }
i.e., cannot balance: ( ), { }, begin end
Regular Grammar
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Regular Expressions
x a character x \x an escaped character, e.g., \n{ name } a reference to a nameM | N M or NM N M followed by NM* zero or more occurrences of MM+ One or more occurrences of MM? Zero or one occurrence of M[aeiou] the set of vowels[0-9] the set of digits. any single character
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Regular Expressions
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Regular Expressions
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(S, a2i$) ├ (I, 2i$)
├ (I, i$)
├ (I, $)
├ (F, )
Thus: (S, a2i$) ├* (F, )
Finite State Automaton for Identifiers
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•
Deterministic Finite State Automaton Examples
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Production:
α → β
α Nonterminal
β (Nonterminal Terminal)*
ie, lefthand side is a single nonterminal, and righthand side is a string of nonterminals and/or terminals (possibly empty).
Context-Free Grammar
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Production:
α → β |α| ≤ |β|
α, β (Nonterminal Terminal)*
ie, lefthand side can be composed of strings of terminals and nonterminals, however, the number of items on the left must be smaller than the number of items on the right.
Context-Sensitive Grammar
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• The syntax of a programming language is a precise description of all its grammatically correct programs.
• Precise syntax was first used with Algol 60, and has been
used ever since.
• Three levels:– Lexical syntax - all the basic symbols of the language
(names, values, operators, etc.)– Concrete syntax - rules for writing expressions,
statements and programs.– Abstract syntax - internal representation of the program,
favoring content over form.
Syntax
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GrammarsGrammars: Metalanguages used to define the concrete syntax of a language.
Backus Normal Form – Backus Naur Form (BNF)• Stylized version of a context-free grammar (cf. Chomsky hierarchy)
• First used to define syntax of Algol 60
• Now used to define syntax of most major languages Production: α → β α Nonterminal β (Nonterminal Terminal)*ie, lefthand side is a single nonterminal, and β is a string of nonterminals and/or terminals (possibly empty).
• ExampleInteger Digit | Integer Digit
Digit 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
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Extended BNF (EBNF)
Additional metacharacters{ } a series of zero or more( ) must pick one from a list[ ] pick none or one from a list
ExampleExpression -> Term { ( + | - ) Term }IfStatement -> if ( Expression ) Statement [ else Statement ]
EBNF is no more powerful than BNF, but its production rules are often simpler and clearer.
Javacc EBNF
( … )* a series of zero or more( … )+ a series of one or more[ … ] optional
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For more details, see Chapter 2 of“Programming Language Pragmatics, Third Edition (Paperback)”Michael L. Scott (Author)
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Internal Parse Tree
Abstract Syntax
int main ()
{
return 0 ;
}
Program (abstract syntax): Function = main; Return type = int params = Block: Return: Variable: return#main, LOCAL addr=0 IntValue: 0
Instance of a Programming Language:
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Now we’ll focus on the internal parse tree
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Parse Trees
Integer Digit | Integer DigitDigit 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
Parse Tree for 352 as an Integer
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Arithmetic Expression Grammar
Expr Expr + Term | Expr – Term | TermTerm 0 | ... | 9 | ( Expr )
Parse of 5 - 4 + 3
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• A grammar can be used to define associativity and precedence among the operators in an expression.
E.g., + and - are left-associative operators in mathematics;
* and / have higher precedence than + and - .
• Consider the following grammar:Expr -> Expr + Term | Expr – Term | Term
Term -> Term * Factor | Term / Factor | Term % Factor | Factor
Factor -> Primary ** Factor | Primary
Primary -> 0 | ... | 9 | ( Expr )
Associativity and Precedence
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Associativity and Precedence
Parse of 4**2**3 + 5 * 6 + 7
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Precedence Associativity Operators3 right **2 left * / %1 left + -
Note: These relationships are shown by the structure of the parse tree: highest precedence at the bottom, and left-associativity on the left at each level.
Associativity and Precedence
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• A grammar is ambiguous if one of its strings has two or more diffferent parse trees.
• Example:Expr -> Expr Op Expr | ( Expr ) | IntegerOp -> + | - | * | / | % | **
• Equivalent to previous grammar but ambiguous
Ambiguous Grammars
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Ambiguous Parse of 5 – 4 + 3
Ambiguous Grammars
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Dangling Else Ambiguous Grammars
IfStatement -> if ( Expression ) Statement |
if ( Expression ) Statement else Statement
Statement -> Assignment | IfStatement | Block
Block -> { Statements }
Statements -> Statements Statement | Statement
With which ‘if’ does the following ‘else’ associate
if (x < 0)if (y < 0) y = y - 1;else y = 0;
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Dangling Else Ambiguous Grammars
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Program : {[ Declaration ]|retType Identifier Function | MyClass | MyObject}
Function : ( ) Block
MyClass: Class Idenitifier { {retType Identifier Function}Constructor {retType Identifier Function } }
MyObject: Identifier Identifier = create Identifier callArgs
Constructor: Identifier ([{ Parameter } ]) block
Declaration : Type Identifier [ [Literal] ]{ , Identifier [ [ Literal ] ] }
Type : int|bool| float | list |tuple| object | string | void
Statements : { Statement }
Statement : ; | Declaration| Block |ForEach| Assignment |IfStatement|WhileStatement|CallStatement|ReturnStatement
Block : { Statements }
ForEach: for( Expression <- Expression ) Block
Assignment : Identifier [ [ Expression ] ]= Expression ;
Parameter : Type Identifier
IfStatement: if ( Expression ) Block [elseifStatement| Block ]
WhileStatement: while ( Expression ) Block
Hmm BNF (i.e., Concrete Syntax)
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Expression : Conjunction {|| Conjunction }
Conjunction : Equality {&&Equality }
Equality : Relation [EquOp Relation ]
EquOp: == | !=
Relation : Addition [RelOp Addition ]
RelOp: <|<= |>|>=
Addition : Term {AddOp Term }
AddOp: + | -
Term : Factor {MulOp Factor }
MulOp: * | / | %
Factor : [UnaryOp]Primary
UnaryOp: - | !
Primary : callOrLambda|IdentifierOrArrayRef| Literal |subExpressionOrTuple|ListOrListComprehension|
ObjFunction
callOrLambda : Identifier callArgs|LambdaDef
callArgs : ([Expression |passFunc { ,Expression |passFunc}] )
passFunc : Identifier (Type Identifier { Type Identifier } )
LambdaDef : (\\ Identifier { ,Identifier } -> Expression)
Hmm BNF (i.e., Concrete Syntax)
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Hmm BNF (i.e., Concrete Syntax)
IdentifierOrArrayRef : Identifier [ [Expression] ]
subExpressionOrTuple : ([ Expression [,[ Expression { , Expression } ] ] ] )
ListOrListComprehension: [ Expression {, Expression } ] | | Expression[<- Expression ] {, Expression[<-
Expression ] } ]
ObjFunction: Identifier . Identifier . Identifier callArgs
Identifier : (a |b|…|z| A | B |…| Z){ (a |b|…|z| A | B |…| Z )|(0 | 1 |…| 9)}
Literal : Integer | True | False | ClFloat | ClString
Integer : Digit { Digit }
ClFloat: 0 | 1 |…| 9 {0 | 1 |…| 9}.{0 | 1 |…| 9}
ClString: ” {~[“] }”
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Clite Operator AssociativityUnary - ! none* / left+ - left< <= > >= none== != none&& left|| left
Associativity and Precedence for Hmm
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Hmm Parse Tree Example
z = x + 2 * y;
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Now we’ll focus on the Abstract Syntax
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Hmm Parse Tree
z = x + 2 * y;
=
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Very Approximate Hmm Abstract Syntax
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Assignment = Variable target; Expression source
Expression = VariableRef | Value | Binary | Unary
VariableRef = Variable | ArrayRef
Variable = String id
ArrayRef = String id; Expression index
Value = IntValue | BoolValue | FloatValue | CharValue
Binary = Operator op; Expression term1, term2
Unary = UnaryOp op; Expression term
Operator = ArithmeticOp | RelationalOp | BooleanOp
IntValue = Integer intValue…
Very Approximate Hmm Abstract Syntax
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Binary
BinaryOperator
Operator
Variable
VariableValue
+
2 y*
x
Hmm Abstract Syntax – Binary Example
z = x + 2 * y
=
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