Functions in Scheme. From Scheme to Java. Functions in Java. Functions in Java. method that is in the class // Determines whether it s < n lbs

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Ethelbert Barrett
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1 From Scheme to Java So far, we ve translated data definitions: ; A snake is ; (make-snake sym num sym) (define-struct snake (name weight food)) class Snake { String name; double weight; String food; Snake(String name, double weight, String food) { this.name = name; this.weight = weight; this.food = food; Functions in Scheme ; A snake is ; (make-snake sym num sym) (define-struct snake (name weight food)) (< (snake-weight s) n)) (snake-lighter? (make-snake Slinky 10 rats) 10) (snake-lighter? (make-snake Slimey 5 grass) 10) Functions in Java class Snake { String name; double weight; String food; Snake(String name, double weight, String food) { this.name = name; this.weight = weight; this.food = food; new Snake("Slinky", 10, "rats").islighter(10) Functions in Java class Snake { String name; double weight; String food; Snake(String name, double weight, String food) { this.name = name; this.weight = weight; A function this.food = food; becomes a method that is in the class new Snake("Slinky", 10, "rats").islighter(10) 1-4

2 (< (snake-weight s) n)) (define (snake-lighter? A method s n) in (< (snake-weight s) Snake n)) has an implicit Snake this // Determines whether argument it s < n lbs All other arguments are explicit, and the (< (snake-weight s) n)) type is next to the name, as in double n (< (snake-weight s) n)) The result type is boolean 5-8

3 Since ; Determines the method takes whether a Snake s is < n lbs and (define double (snake-lighter? and produces a s n) boolean, (< (snake-weight the contract is s) n)) Snake double -> boolean and we don t write it as a comment Purpose comment is as (< (snake-weight in Scheme, s) n)) but comments start with // (< (snake-weight s) Instead n)) of (snake-weight s) use // Determines whether this.weight it s < n lbs (< (snake-weight s) n)) Explicitly designate the result with // Determines returnwhether it s < n lbs 9-12

4 return First this.weight the purpose, starting < n; with // Then the result type Then the method name (not capitalized, by convention) 13-16

5 Start arguments with ( Arguments except for this use a type for each argument, and separate multiple arguments with, End arguments with ) Then a { 17-20

6 Body using Java notation, put return before a result Put ; after a result End with Original tests: (snake-lighter? (make-snake Slinky 10 rats) 10) new Snake("Slinky", 10, "rats").islighter(10) 21-24

7 Constant "should definition be" false starts with the constant s type Then the name Then = 25-28

8 Then an "should be" expression false End with ; Method call starts with an expression for the implicit this argument Then

9 Then the method name Then ( Then expressions for the explicit arguments separated by, Then ) 33-36

10 Templates Templates In ; A snake is ; (make-snake sym num sym) (define-struct snake (name weight food)) ; func-for-snake : snake ->... (define (func-for-snake s)... (snake-name s)... (snake-weight s)... (snake-food s)...) Same idea works for class Snake { String name; double weight; String food; Snake(String name, double weight, String food) { this.name = name; this.weight = weight; this.food = food;... methodforsnake(...) {... this.name... this.weight... this.food... More Examples Implement a feed method for Snake which takes an amount of food in pounds and produces a fatter snake Lists in Java Translate the list-of-num data definition to Java and implement a length method Implement a feed method for Dillo and Ant Implement a feed method for Animal 37-40

From Scheme to Java. So far, we ve translated data definitions: ; A snake is ; (make-snake sym num sym) (define-struct snake (name weight food))

From Scheme to Java. So far, we ve translated data definitions: ; A snake is ; (make-snake sym num sym) (define-struct snake (name weight food)) From Scheme to Java So far, we ve translated data definitions: ; A snake is ; (make-snake sym num sym) (define-struct snake (name weight food)) class Snake { String name; double weight; String food; Snake(String