The Design Recipe Fall 2018

Transcription

1 CS17 Integrated Introduction to Computer Science Klein The Design Recipe Fall 2018 Contents 1 Design Recipe Steps 1 2 Another Racket Example 6 3 An OCaml Example 6 4 Another OCaml Example 8 1 Design Recipe Steps This PDF outlines the steps to writing the design recipe; each step is accompanied by part of an example for writing the design recipe. The example function is in Racket, and it determines whether or not a database is empty. 1. Provide data definitions for all non-atomic data types - that is, anything but numbers, strings, and booleans. (If multiple procedures in a single file use the same non-atomic types, provide these data definitions once at the top of the file, not once-per-procedure). Data definition: (string list): empty (cons string (string list)) database: (string list) 2. Provide examples of the data the procedure will process and produce. Data definition: (string list): empty (cons string (string list)) database: (string list) Example data: string: "cat", "dog" (string list): (cons "cat" (cons "dogs" empty))

2 3. Specify the procedures type signature, which describes the type of data the procedure consumes, and the type it produces. Your types should be meaningful Racket types, like string, int, real, and <type> list. A more specific type with no semantic meaning in Racket something like nonnegative integer should be specified in the I/O contract rather than the type signature. A procedure consuming nonnegative integers would just have the input type int and the more detailed description of the nonnegative constraint in the I/O contract. Data Definition Example data: string: "Carmen", "Audrey", "dog" A database is a list of strings Examples: bool: true, false is - database - empty?: database - > bool 4. Following the type signature, describe the procedure s call structure, i.e., give names to the procedure and its arguments. (This involves writing the start of a Racket program rather than writing a comment.) Data Definition Example data: string: "Carmen", "Audrey", "dog" A database is a list of strings Examples: bool: true, false is - database - empty?: database - > bool...) 2

3 5. Write a specification for the procedure. That is, in words, not code, state the relationship between the procedures input and output (make sure to use the argument names you created in the call structure). This goes in a comment above the call structure. Writing the spec may include restricting the domain in the description of some variable, for instance declaring an input as nonnegative. Data Definition Example data: string: "Carmen", "Audrey", "dog" A database is a list of strings Examples: bool: true, false is - database - empty?: database - > bool input: db, a database output: a boolean that is true if db is empty, and false if it is not...) 6. Provide test cases that exemplify the procedure s operation. These tests must follow its call structure and satisfy its specification. Data Definition Example data: string: "Carmen", "Audrey", "dog" A database is a list of strings Examples: bool: true, false is - database - empty?: database - > bool input: db, a database output: a boolean that is true if db is empty, and false if it is not...) Test cases (check - expect (is - database - empty? empty) true) (check - expect (is - database - empty? (cons "hedwig" empty)) false) 3

4 7. Write the template for the procedure based on the data definition and the type signature. This is where you would decide whether to use an if-statement or a cond-expression. Data Definition Example data: string: "Carmen", "Audrey", "dog" A database is a list of strings Examples: bool: true, false is - database - empty?: database - > bool input: db, a database output: a boolean that is true if db is empty, and false if it is not (cond [(empty? db)...] [(cons? db)...])) Test cases (check - expect (is - database - empty? empty) true) (check - expect (is - database - empty? (cons "hedwig" empty)) false) 4

5 8. Code the procedure. Specifically, fill in the template clause by clause. For each of the possible input types, decide which fields in the input structures are relevant to the problem at hand, and figure out how to operate on them to generate the desired output. Data Definition Example data: string: "Carmen", "Audrey", "dog" A database is a list of strings Examples: bool: true, false is - database - empty?: database - > bool input: db, a database output: a boolean that is true if db is empty, and false if it is not (cond [(empty? db) true] [(cons? db) false])) Test cases (check - expect (is - database - empty? empty) true) (check - expect (is - database - empty? (cons "hedwig" empty)) false) 9. Run your program on your test cases. 5

6 2 Another Racket Example This is another Racket program, listlength, with the completed design recipe - to find the length of a float list. Data Definition Example data: float: 7.8, A float list is a list of floats Examples: (define alof1 empty) (define alof2 (cons (cons 6.7 empty))) int: 4, 0, - 11 listlength: (float list) - > int input: alof, a float list output: an int that represents the number of elements in flist (define (listlength alof) (length alof)) Test cases (check - expect (listlength empty) 0) (check - expect (listlength (cons 65.6 (cons 8.9 empty))) 2) 3 An OCaml Example (* Data Definition * Example data: * string: "Carmen", "Audrey", "dog" * * A database is a list of strings * Examples: *) [] ["cat"; "dog"] (* bool: true, false * * input: db, a database * output: a boolean that is true if db is empty, and false if it is not *) let isdatabaseempty (db: string list) : bool = match db with [] - > true 6

7 _ - > false (* test cases *) check_expect (isdatabaseempty []) true check_expect (isdatabaseempty ["the"; "design"; "recipe") false 7

8 4 Another OCaml Example This is another OCaml program, iszero, with the completed design recipe - to determine if an integer is zero. (* Data Definition * Example data: * int: - 1, 0, 1*) (*Input: an integer, int Output: a boolean, true if the integer is 0, false otherwise*) let iszero (int: integer) : boolean = match int with 0 - > true _ - > false check_expect iszero(0) true; check_expect iszero(1) false; check_expect iszero( - 5) false; Please let us know if you find any mistakes, inconsistencies, or confusing language in this or any other CS 17 document by filling out the anonymous feedback form: courses/csci0170/feedback. 8