Pairs and Lists in The Racket Guide introduces pairs and lists. A pair combines exactly two values. The first value is accessed with the car procedure, and the second value is accessed with the cdr procedure. … A list is recursively defined: it is either the constant null, or it is a pair whose second value is a list.
Correspondingly, what is a thunk in racket?
A zero-argument function used to delay evaluation is called a thunk. – As a verb: thunk the expression. This works (but it is silly to wrap if like this): 3. (define (my-if x y z)
Likewise, how do you sort a list in racket?
What is null in Scheme?
In Scheme, there is one null pointer value, called “the empty list,” which prints as () . … Conceptually, the empty list is a special object, and a “null” pointer is a pointer to this special end-of-list object.
What does let do in racket?
Local Binding: let, let*, letrec, … in The Racket Reference also documents let. A let form binds a set of identifiers, each to the result of some expression, for use in the let body: (let ([id expr] …)
Are streams in racket Memoized?
The expressions passed to stream-cons are not evaluated until requested either with stream-first or stream-rest . Once evaluated, they are memoized.
Why is it called thunk?
In computer programming, a thunk is a subroutine used to inject a calculation into another subroutine. … The term originated as a whimsical irregular form of “think.” It refers to the original use of thunks in ALGOL compilers, which required special analysis (thought) to determine what type of routine to generate.
Is thunk a closure?
Is the first article author wrong about what is a thunk and is it right to say a thunk is a specific kind of closure “that contains all of the context (state, functions, etc) it will need in order to carry out some sort of logic in the future.”
What does car stand for Lisp?
In computer programming, CAR ( car ) /kɑːr/ ( listen) and CDR ( cdr ) (/ˈkʌdər/ ( listen) or /ˈkʊdər/ ( listen)) are primitive operations on cons cells (or “non-atomic S-expressions”) introduced in the Lisp programming language.
What’s a CDR?
Call Detail Record (CDR) is the detailed record of all the telephonic calls that pass through a telephone exchange or any other telecommunications equipment.
What CDR means?
also CDR. title noun. Cdr is the written abbreviation for Commander when it is used as a title.