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Questions tagged [let]

In Lisp-like and functional languages, introduces a list of local variables, each (possibly optionally) with its initial value.

In Lisp-like and functional languages, introduces a list of local variables, each (possibly optionally) with its initial value. It is illegal to refer to any of the new variables while calculating their initial values ( lets you do that), though in Haskell it is legal (its let is actually letrec).

LET is a special form in Common Lisp, Scheme, Clojure and other Lisp dialects which introduces a list of local variables as pairs of name-value bindings, for use within its body. For instance, in this expression:

(let ((variable1 (+ 1 1)))
  variable1)

variable1 gets bound to the 2 value, and the whole expression returns 2 as a result.

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Let variables and block scope

Why does the first console log print out "James" when it should print out "Ken"? Shouldn't the let 'student' variable be scope to the 'if-statement' and retain its value as "Ken"? Also, shouldn't there be an error as I'm redeclaring the same…
Johnny G.
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Common Lisp let function

I'm just starting to program in Common Lisp and going back through programs that I coded during some of my previous classes to learn and I am having trouble understanding the problem in my code. (defun input-1 () (defvar *message*…
Mitchell
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How to use let declarations as expressions?

I want to use let expressions, but the following code doesn't work: true ? (let x=1, let y=2, x+y) : (let x=3, let y=4, x-y); // SyntaxError How am I supposed to do this?
user6445533
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Rspec let hash key unexpected =>, expecting '}'

I am confusing in using ruby hash key format and let. This works in normal case. { "id" => 1, "description" => "test 3", "difficulty" => { "id" => 1, "description" => "easy" }, } but fails in let block Here's the code: describe…
rj487
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Undefined symbols for architecture x86_64 flex/bison

I am trying to make a simple toy (LET) language as practice using flex/bison. However, I keep getting the following error when I run the command g++ -Wall -std=c++11 repl.cpp -v -o LET: Undefined symbols for architecture x86_64: …
M. Barbieri
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Scheme using input parameter in inner function

I'm new to Scheme and to functional programming in general. As part of an exercise, I try to implement a function that that takes a number n and prints line by line first n Fibonacci numbers The problem is that when the program reaches the recursive…
Noam
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Haskell let ..... in let ..... in let

got some code to complete. But I don't know how to handle the nasted let in expression. Thats the code: data Zutat = Tomate | Fleisch | Salat data Bun = Weizen | Roggen data Sosse = Ketchup Sosse | Mayo Sosse | Keine data Burger = Burger Bun…
Benedict K.
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Clojure, replacing vars in let bindings causes performance issue?

Let's say there is a function and it received a json string which contains about 100KB of data. The string gets converted to a map and then it keeps associating new keys to that map and replacing the var in let bindings like below: (defn myfn …
gini09
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Unable to declare a variable within *ngFor angular2

I am trying to declare a variable of my own within *ngFor but it throws error and is not working. I loop through a collection of buttons, and show icon whenever the condition inside *ngIf is satisfied.
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Why 'if let' does not seem to unbox a value as before in Swift 3 in Xcode 8.3 beta?

Unlike before, I was surprised to see that 'title' is now an optional (the compiler now generates the waning : String interpolation produces a debug description for an optional value; did you mean to make this explicit?). How it comes the 'if let…
Stéphane de Luca
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Ocaml syntax error in a simple if-then-else

I want to change some code written in C into Ocaml Here is a C code int a, b; if(m > n) { a = n; b = m; } else { a = m; b = n; } and I tried to change it into Ocaml but somehow I got a syntax error at the second line. let rec gcd…
Dagoo Mong
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Mozilla Possible let vs var Bug

Please consider the following JavaScript code: let funcs = [] for(let x of [1,2,3]) { funcs[x] = function(){ console.log("test:", x) } } funcs[1]() funcs[2]() funcs[3]() When I run this code in Google Chrome V55.0 it generates the…
d3newguy
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If let statement error

Im trying to build a todo list with coreData, my goal is to have an error pop-up notification if a user tries to just click the "add" button without entering any text in the text-field. I currently have the pop-up notification working but once i…
user7417272
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Is let a get only variable?

I'm a little bit confused with this. We have variables in swift that can have a setter, getter or both and constants which can't change his own initial value, So, is a var with only a getter the same as a let? If it is, what is the idea in a…
user3175133
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let: bad syntax (not an identifier and expression for a binding) in: wordslist ###scheme

(define (most-common-word str) (let (wordslist str-split str " "))) I am trying to do a inner variable of lists of strings. but I get the error "bad syntax". I looked for answers here but the things I changed, didn't help. str-split returns a…
shay C
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