@stdlib/iter/pipeline-thunk/README.md

Standard iterator utilities.

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# iterThunk

> Create an [iterator][mdn-iterator-protocol] "thunk".

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## Usage

```javascript
var iterThunk = require( '@stdlib/iter/pipeline-thunk' );
```

#### iterThunk( iterFcn\[, ...args] )

Returns an [iterator][mdn-iterator-protocol] "thunk".

```javascript
var array2iterator = require( '@stdlib/array/to-iterator' );
var iterSome = require( '@stdlib/iter/some' );

var thunk = iterThunk( iterSome, 3 );

var arr = array2iterator( [ 0, 0, 1, 1, 1 ] );
var bool = thunk( arr );
// returns true

arr = array2iterator( [ 0, 0, 1, 0, 1 ] );
bool = thunk( arr );
// returns false
```

A provided [iterator][mdn-iterator-protocol] function should have the following function signature:

```text
function iterFcn( iterator[, ...args] ) {...}
```

where

-   **iterator**: an [iterator][mdn-iterator-protocol]
-   **...args**: additional [iterator][mdn-iterator-protocol] function arguments

The returned function expects a single argument

-   **iterator**: an [iterator][mdn-iterator-protocol]

and invokes `iterFcn` with the provided [iterator][mdn-iterator-protocol] and any previously provided `args`.

Accordingly, this function implements left-to-right [partial application][@stdlib/utils/papply] with special consideration for functions which act upon [iterator][mdn-iterator-protocol] sequences.

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## Notes

-   This function is useful within the context of [iterator][mdn-iterator-protocol] pipelines as a means to defer execution until a pipeline is ready for data flow.
-   The function evaluation context is **always** `null`.

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## Examples

<!-- eslint-disable function-call-argument-newline, function-paren-newline -->

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```javascript
var randu = require( '@stdlib/random/iter/randu' );
var iterHead = require( '@stdlib/iter/head' );
var iterMap = require( '@stdlib/iter/map' );
var iterSome = require( '@stdlib/iter/some' );
var iterPipeline = require( '@stdlib/iter/pipeline' );
var iterThunk = require( '@stdlib/iter/pipeline-thunk' );

function threshold( r ) {
    return ( r > 0.95 );
}

// Create a pipeline which tests whether at least 5% of values exceed a threshold:
var p = iterPipeline(
    // Apply a threshold to iterated values:
    iterThunk( iterMap, threshold ),

    // Limit the sequence to 100 values:
    iterThunk( iterHead, 100 ),

    // Test whether at least 5 values exceed the threshold:
    iterThunk( iterSome, 5 )
);

// Define the number of random number sequences to analyze:
var N = 100;

// Initialize a counter for sequences satisfying the 5% threshold:
var count = 0;

// Perform analysis...
var bool;
var i;
for ( i = 0; i < N; i++ ) {
    bool = p( randu() );
    if ( bool ) {
        count += 1;
    }
    console.log( bool );
}
console.log( '%d of %d', count, N );
```

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* * *

## See Also

-   <span class="package-name">[`@stdlib/iter/pipeline`][@stdlib/iter/pipeline]</span><span class="delimiter">: </span><span class="description">create an iterator pipeline.</span>

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[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol

[@stdlib/utils/papply]: https://www.npmjs.com/package/@stdlib/utils-papply

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[@stdlib/iter/pipeline]: https://github.com/stdlib-js/iter/tree/main/pipeline

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