CS 3721: Programming Languages Lab
Lab #03: Higher order functions in Scheme
Due date: February 12, 3:30pm. At the beginning of the next recitation.
Goals of this lab:
โขLearn to use let* ;Be able to define and use higher-order functions ;More recursion
1. The operator, let*. This operator is used for variable bindings, and has the following
syntax:
(letโ< bindings > < body >)
< bindings > should have the form
((< variable1> < init1>). . .),
where each < init > is an expression, and < body > should be a sequence of one or more
expressions. The bindings are performed sequentially from left to right. Therefore, the
second binding is done in an environment in which the first binding is visible, and so on.
An example:
(let* ((x 7) ; first binding
(y 3) ; second binding
(z (+ x y))) ; third binding: first and second bindings are visible
(* z x y)) ; <body>: you can use your <bindings> in the <body>
=> 210
Given the lengths of the legs of several right triangles in a list, define a recursive function
calcHypotenuse which calculates the hypotenuses of the triangles using the let* operator.
Hint: You may want to embed the following template into the else part of the check for
whether the input list is null.
(let*
((triangle <expression for evaluating triangle, you may use your input list>)
(leg1 <expression for evaluating leg1, you may use triangle>) ; second binding
(leg2 <expression for evaluating leg2, you may use triangle>) ; third binding
(hypotenuse <expression for evaluating hypotenuse> )) ; forth binding
(... hypotenuse ...) ; <body>
)
Test your function with the expression below.
> (calcHypotenuse โ((5 12) (3 4) (7 24) (8 15)))
(list 13 5 25 17)
1
