CSE240 Lecture 03

Introduction to Programming Languages
Structure of Programming Languages
(202001)

Transcript

1. jgs
   CSE 240
   Introduction to Programming Languages
   Lecture 03: Structure of Programming Languages
   Dr. Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu | javiergs.com
   PERALTA 230U
   Office Hours: By appointment
   

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2. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 2
   jgs
   Structure of a Programming Language
   Paradigm
   Language Rules
   Lexical
   Input:
   Symbols
   Output:
   Words
   Syntax
   Input:
   Words
   Output:
   Sentences
   Semantic
   Input:
   Sentences
   

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3. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 3
   jgs
   Lexical Rules - Definition
   Create words
   Concatenate symbols
   until you found a whitespace,
   an operator, or a delimiter
   

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4. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 4
   jgs
   Lexical Rules - Algorithm
   do {
   String word = "";
   char c = getNextCharacter();
   if (c is not an operator nor a delimiter nor a whitespace nor EndOfLine)
   word = word + c;
   } else {
   if (word is a literal or
   word is a keyword or
   word is an identifier){
   // This word is correct J
   } else {
   // Houston, we have a lexical error L
   }
   word = "";
   }
   } while (fileHasMoreCharacters());
   

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5. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 5
   jgs
   Lexical Rules - Example
   int x = ; 5 float 3y = "hello;
   String@z="9.5”;intx=cse240;if(x> 14)
   while
   (5 == 5) if (int a) a = 1; x = x;
   for ( ; ; );y = 13.45.0;int me
   =99999000001111222000000111111222223
   443483045830948;while { x != 9}
   ();int {x} = 10;
   

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6. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 6
   jgs
   Lexical Rules - Example
   int x = ;
   5 float 3y = "hello;
   String@z = "9.5";
   intx = cse240;
   if ( x > 14) while (5 == 5) if (int a) a = 1;
   x = x; for ( ; ; );
   y = 13.45.0;
   int me =99999000001111222000000111111222223
   443483045830948;
   while { x != 9} ();
   int {x} = 10;
   

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7. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 7
   jgs
   Lexical Rules - Tokens
   § Identifiers. Names (programmer chosen) for something of interest (variables,
   functions, methods, classes, etc.) 

   § Keywords. names reserved by the language designer: if, switch, for, int, float, char,
   while, etc.
   § Operators. +, *, <, >=, !, &&, ||, etc.
   § Delimiters. , ; ( ) { }
   § Literals. 5, 14.5, 'A', "Hello",
   § Comments. /* ... */, // ...
   

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8. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 8
   jgs
   Structure of a Programming Language
   Create sentences
   by combining words
   

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9. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 9
   jgs
   Syntactic Rules - Grammar
   

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10. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 10
    jgs
    Syntactic Rules - Example
    sum4 = (a1 + a2) * (3*b % 4*b)_
    p4rd2 = ((a + a2) * (b3 % b4)) hi (c7 - c8);
    foo_bar = (a1 + a2 - b3 - b4);
    (a1 / a2) = (c3 - c4);
    if (z<4) }
    while ( 5 ) { if ( 6 ) { } }
    

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11. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 11
    jgs
    Structure of a Programming Language
    Paradigm
    Language Rules
    Lexical
    Input:
    Symbols
    Output:
    Words
    Syntax
    Input:
    Words
    Output:
    Sentences
    Semantic
    Input:
    Sentences
    

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12. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 12
    jgs
    Structure of a Programming Language
    Review that the sentences are
    meaningful
    Run-Time
    Errors
    

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13. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 13
    jgs
    Semantic Rules
    1.Declaration and Unicity. Review for uniqueness and that the variable has been
    declared before its usage.
    2.Types. Review that the types of variables match the values assigned to them.
    3.Array’s indexes. Review that the indexes are integers.
    4.Conditions. Review that all expressions on the conditons return a boolean value.
    5.Return type. Review that the value returned by a method match the type of the
    method.
    6.Parameters. Review that the parameters in a method match in type and number
    with the declaration of the method.
    

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14. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 14
    jgs
    Semantic Rules
    Declaration and Unicity:
    Review for uniqueness and that the variable has been declared before its
    usage.
    //Case 1:
    int i;
    char j; int m;
    void method(int n, char c) {
    int n; short l;
    i = j; i = m;
    }
    //Case 2:
    int i, j;
    void method() {
    int i = 5;
    int j = i + i;
    int i = i + i;
    }
    

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15. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 15
    jgs
    Semantic Rules
    1.Declaration and Unicity. Review for uniqueness and that the variable has been
    declared before its usage.
    2.Types. Review that the types of variables match the values assigned to them.
    3.Array’s indexes. Review that the indexes are integers.
    4.Conditions. Review that all expressions on the conditons return a boolean value.
    5.Return type. Review that the value returned by a method match the type of the
    method.
    6.Parameters. Review that the parameters in a method match in type and number
    with the declaration of the method.
    

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16. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 16
    jgs
    Semantic Rules
    Types:
    Review that the types of variables match the values assigned to them.
    //Case 3:
    int x = "hello";
    char c = false;
    boolean foo = c;
    

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17. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 17
    jgs
    Semantic Rules
    1.Declaration and Unicity. Review for uniqueness and that the variable has been
    declared before its usage.
    2.Types. Review that the types of variables match the values assigned to them.
    3.Array’s indexes. Review that the indexes are integers.
    4.Conditions. Review that all expressions on the conditons return a boolean value.
    5.Return type. Review that the value returned by a method match the type of the
    method.
    6.Parameters. Review that the parameters in a method match in type and number
    with the declaration of the method.
    

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18. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 18
    jgs
    Structure of a Programming Language
    Run-Time
    Errors
    Paradigm
    Language Rules
    Lexical
    Input:
    Symbols
    Output:
    Words
    Syntax
    Input:
    Words
    Output:
    Sentences
    Semantic
    Input:
    Sentences
    

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19. Javier Gonzalez-Sanchez | CSE240 | Fall 2021 | 19
    jgs
    Questions
    

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20. jgs
    CSE 240 Introduction to Programming Languages
    Javier Gonzalez-Sanchez, Ph.D.
    javiergs@asu.edu
    Fall 2021
    Copyright. These slides can only be used as study material for the class CSE240 at Arizona State University.
    They cannot be distributed or used for another purpose.
    

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