Editing Set-builder notation (section)

== In programming languages ==
{{main article|List comprehension}}

A similar notation available in a number of [[programming languages]] (notably [[Python (programming language)|Python]] and [[Haskell (programming language)|Haskell]]) is the [[list comprehension]], which combines [[map (higher-order function)|map]] and [[filter (higher-order function)|filter]] operations over one or more [[list (computing)|lists]].

{{section move from|List comprehension|date=December 2023|discuss=Talk:Set-builder notation#Move programming language details and comparison into List comprehension}}

In Python, the set-builder's braces are replaced with square brackets, parentheses, or curly braces, giving list, [[generator (computer science)|generator]], and set objects, respectively. Python uses an English-based syntax. Haskell replaces the set-builder's braces with square brackets and uses symbols, including the standard set-builder vertical bar.

The same can be achieved in [[Scala (programming language)|Scala]] using Sequence Comprehensions, where the "for" keyword returns a list of the yielded variables using the "yield" keyword.<ref>{{cite web | publisher=Scala | url=http://docs.scala-lang.org/tutorials/tour/sequence-comprehensions.html | title=Sequence Comprehensions | access-date=6 August 2017 }}</ref>

Consider these set-builder notation examples in some programming languages:
{| class="wikitable"
|-
! !! Example 1 !! Example 2
|-style="text-align:center;"
! Set-builder
| <math>\{l\ |\ l \in L\}</math> || <math>\{(k, x)\ |\ k \in K \wedge x \in X \wedge P(x) \}</math>
|-
! scope="row" | [[Python (programming language)|Python]]
| <syntaxhighlight lang="python">{l for l in L}</syntaxhighlight> || <syntaxhighlight lang="python">{(k, x) for k in K for x in X if P(x)}</syntaxhighlight>
|-
! scope="row" | [[Haskell (programming language)|Haskell]]
| <syntaxhighlight lang="haskell">[l | l <- ls]</syntaxhighlight> || <syntaxhighlight lang="haskell">[(k, x) | k <- ks, x <- xs, p x]</syntaxhighlight>
|-
! scope="row" | [[Scala (programming language)|Scala]]
| <syntaxhighlight lang="scala">for (l <- L) yield l</syntaxhighlight> || <syntaxhighlight lang="scala">for (k <- K; x <- X if P(x)) yield (k,x)</syntaxhighlight>
|-
! scope="row" | [[C Sharp (programming language)|C#]]
| <syntaxhighlight lang="csharp">from l in L select l</syntaxhighlight> || <syntaxhighlight lang="csharp">from k in K from x in X where P(x) select (k,x)</syntaxhighlight>
|-
! scope="row" | [[SQL]]
| <syntaxhighlight lang="sql">SELECT l FROM L_set</syntaxhighlight> || <syntaxhighlight lang="sql"> SELECT k, x FROM K_set, X_set WHERE P(x)</syntaxhighlight>
|-
! scope="row" | [[Prolog]]
| <syntaxhighlight lang="prolog">setof(L,member(L,Ls),Result)</syntaxhighlight> || <syntaxhighlight lang="prolog">setof((K,X),(member(K,Ks),member(X,Xs),call(P,X)),Result)</syntaxhighlight>
|-
![[Erlang (programming language)|Erlang]]
|<syntaxhighlight lang="erlang">
[L || L <- Ls]


</syntaxhighlight>
|<syntaxhighlight lang="erlang">
[{K,X} || K <- Ks, X <- Xs, p(X)]


</syntaxhighlight>
|-
![[Julia (programming language)|Julia]]
|<syntaxhighlight lang="julia">[l for l ∈ L]</syntaxhighlight>
|<syntaxhighlight lang="julia">
[(k, x) for k ∈ K for x ∈ X if P(x)]
</syntaxhighlight>
|-
![[Wolfram Mathematica|Mathematica]]
|<syntaxhighlight lang="mathematica">
(l |-> l) /@ L
</syntaxhighlight>
|<syntaxhighlight lang="mathematica">
Cases[Tuples[{K, X}], {k_, x_} /; P[x]]
</syntaxhighlight>
|}

The set builder notation and list comprehension notation are both instances of a more general notation known as ''monad comprehensions'', which permits map/filter-like operations over any [[monad (functional programming)|monad]] with a [[zero element]].