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# DA.Foldable
> Reference documentation for Daml module DA.Foldable.
# DA.Foldable
Class of data structures that can be folded to a summary value.
It's a good idea to import this module qualified to avoid clashes with
functions defined in `Prelude`. Ie.:
```
import DA.Foldable qualified as F
```
## Module Snapshot
Stable.
Status: `active`
Introduced in: `3.4.9`
Removed in: `-`
Warnings: `0`
Deprecations: `0`
Deprecated since: `-`
## Typeclasses
### `class Foldable t`
Class of data structures that can be folded to a summary value.
Methods:
* `fold` : [`Monoid`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-monoid-6742) `m` => `t` `m` -> `m`
Combine the elements of a structure using a monoid.
* `foldMap` : [`Monoid`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-monoid-6742) `m` => (`a` -> `m`) -> `t` `a` -> `m`
Combine the elements of a structure using a monoid.
* `foldr` : (`a` -> `b` -> `b`) -> `b` -> `t` `a` -> `b`
Right-associative fold of a structure.
* `foldl` : (`b` -> `a` -> `b`) -> `b` -> `t` `a` -> `b`
Left-associative fold of a structure.
* `foldr1` : (`a` -> `a` -> `a`) -> `t` `a` -> `a`
A variant of foldr that has no base case, and thus should only be applied to non-empty structures.
* `foldl1` : (`a` -> `a` -> `a`) -> `t` `a` -> `a`
A variant of foldl that has no base case, and thus should only be applied to non-empty structures.
* `toList` : `t` `a` -> \[`a`]
List of elements of a structure, from left to right.
* `null` : `t` `a` -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)
Test whether the structure is empty. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.
* `length` : `t` `a` -> [`Int`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-int-37261)
Returns the size/length of a finite structure as an `Int`. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.
* `elem` : [`Eq`](/appdev/reference/daml-standard-library/prelude#class-ghc-classes-eq-22713) `a` => `a` -> `t` `a` -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)
Does the element occur in the structure?
* `sum` : [`Additive`](/appdev/reference/daml-standard-library/prelude#class-ghc-num-additive-25881) `a` => `t` `a` -> `a`
The sum function computes the sum of the numbers of a structure.
* `product` : [`Multiplicative`](/appdev/reference/daml-standard-library/prelude#class-ghc-num-multiplicative-10593) `a` => `t` `a` -> `a`
The product function computes the product of the numbers of a structure.
* `minimum` : [`Ord`](/appdev/reference/daml-standard-library/prelude#class-ghc-classes-ord-6395) `a` => `t` `a` -> `a`
The least element of a non-empty structure.
* `maximum` : [`Ord`](/appdev/reference/daml-standard-library/prelude#class-ghc-classes-ord-6395) `a` => `t` `a` -> `a`
The largest element of a non-empty structure.
Instances:
* instance [`Ord`](/appdev/reference/daml-standard-library/prelude#class-ghc-classes-ord-6395) `k` => [`Foldable`](#class-da-foldable-foldable-25994) ([`Map`](/appdev/reference/daml-standard-library/prelude#type-da-internal-lf-map-90052) `k`)
* instance [`Foldable`](#class-da-foldable-foldable-25994) [`TextMap`](/appdev/reference/daml-standard-library/prelude#type-da-internal-lf-textmap-11691)
* instance [`Foldable`](#class-da-foldable-foldable-25994) [`Optional`](/appdev/reference/daml-standard-library/prelude#type-da-internal-prelude-optional-37153)
* instance [`Foldable`](#class-da-foldable-foldable-25994) [`NonEmpty`](/appdev/reference/daml-standard-library/da-nonempty-types#type-da-nonempty-types-nonempty-16010)
* instance [`Foldable`](#class-da-foldable-foldable-25994) [`Set`](/appdev/reference/daml-standard-library/da-set#type-da-set-types-set-90436)
* instance [`Foldable`](#class-da-foldable-foldable-25994) ([`Validation`](/appdev/reference/daml-standard-library/da-validation#type-da-validation-types-validation-39644) `err`)
* instance [`Foldable`](#class-da-foldable-foldable-25994) ([`Either`](/appdev/reference/daml-standard-library/prelude#type-da-types-either-56020) `a`)
* instance [`Foldable`](#class-da-foldable-foldable-25994) [`[]`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-x-2599)
* instance [`Foldable`](#class-da-foldable-foldable-25994) `a`
## Functions
### `mapA_`
`mapA_` : ([`Foldable`](#class-da-foldable-foldable-25994) `t`, [`Applicative`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-applicative-9257) `f`) => (`a` -> `f` `b`) -> `t` `a` -> `f` ()
Map each element of a structure to an action, evaluate these
actions from left to right, and ignore the results. For a version
that doesn't ignore the results see 'DA.Traversable.mapA'.
### `forA_`
`forA_` : ([`Foldable`](#class-da-foldable-foldable-25994) `t`, [`Applicative`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-applicative-9257) `f`) => `t` `a` -> (`a` -> `f` `b`) -> `f` ()
'for\_' is 'mapA\_' with its arguments flipped. For a version
that doesn't ignore the results see 'DA.Traversable.forA'.
### `forM_`
`forM_` : ([`Foldable`](#class-da-foldable-foldable-25994) `t`, [`Applicative`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-applicative-9257) `f`) => `t` `a` -> (`a` -> `f` `b`) -> `f` ()
### `sequence_`
`sequence_` : ([`Foldable`](#class-da-foldable-foldable-25994) `t`, [`Action`](/appdev/reference/daml-standard-library/prelude#class-da-internal-prelude-action-68790) `m`) => `t` (`m` `a`) -> `m` ()
Evaluate each action in the structure from left to right,
and ignore the results. For a version that doesn't ignore the
results see 'DA.Traversable.sequence'.
### `concat`
`concat` : [`Foldable`](#class-da-foldable-foldable-25994) `t` => `t` \[`a`] -> \[`a`]
The concatenation of all the elements of a container of lists.
### `and`
`and` : [`Foldable`](#class-da-foldable-foldable-25994) `t` => `t` [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265) -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)
`and` returns the conjunction of a container of Bools. For the result to be `True`, the container must be finite; `False`, however, results from a `False` value finitely far from the left end.
### `or`
`or` : [`Foldable`](#class-da-foldable-foldable-25994) `t` => `t` [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265) -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)
`or` returns the disjunction of a container of Bools. For the result to be `False`, the container must be finite; `True`, however, results from a `True` value finitely far from the left end.
### `any`
`any` : [`Foldable`](#class-da-foldable-foldable-25994) `t` => (`a` -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)) -> `t` `a` -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)
Determines whether any element of the structure satisfies the predicate.
### `all`
`all` : [`Foldable`](#class-da-foldable-foldable-25994) `t` => (`a` -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)) -> `t` `a` -> [`Bool`](/appdev/reference/daml-standard-library/prelude#type-ghc-types-bool-66265)
Determines whether all elements of the structure satisfy the predicate.