• egg

## combinators

Combinators grab-bag.

## Documentation

### Section Combinators

#### Usage

`(import section-combinators)`

FUNC a procedure.

#### left-section

[procedure] (left-section FUNC ARG0 ...) => procedure

Returns a procedure that partially applies some of its arguments from the left.

ARG0 ... a prefix of the arguments for FUNC.

Returns a partially curried procedure.

#### right-section

[procedure] (right-section FUNC ARG0 ...) => procedure

Returns a procedure that partially applies some of its arguments from the right.

ARG0 ... a suffix of the arguments for FUNC.

Returns a partially curried procedure.

#### crop-left

[procedure] (crop-left FUNC N) => procedure

Returns a procedure that drops the N left arguments before applying FUNC.

#### crop-right

[procedure] (crop-right FUNC N) => procedure

Returns a procedure that drops the N right arguments before applying FUNC.

#### reversed

[procedure] (reversed FUNC) => procedure

Returns a procedure that reverses the arguments before applying FUNC.

#### arguments-chain

[procedure] (arguments-chain [FUNC0...]) => procedure

Returns a procedure that applies each FUNCi to result of the FUNCi+1. FUNCn is applied to the arguments.

Examples:

`((arguments-chain f g h) arg...) -> (apply f (apply g (apply h arg...)))`
`((arguments-chain f) arg...) -> (apply f arg...)`
`((arguments-chain) arg...) -> (list arg...)`

#### arguments-each

[procedure] (arguments-each [FUNC0...]) => procedure

Returns a procedure that calls each FUNCi to the ARGi. The result is returned as a list. The FUNC0... are re-used until the argument list is exhausted.

Examples:

`((arguments-each f g h) a b c d e) -> (list (f a) (g b) (h c) (f d) (g e))`
`((arguments-each f g h) a b c) -> (list (f a) (g b) (h c))`
`((arguments-each) arg...) -> (list arg...)`

#### arguments-all

[procedure] (arguments-all [FUNC0...]) => procedure

Returns a procedure that calls each FUNCi with all the arguments. The result is returned as a list.

Examples:

`((arguments-all f g h) a b c) -> (list (f a b c) (g a b c) (h a b c))`
`((arguments-all) arg...) -> (list arg...)`

### Sort Combinators

Except for make-less-than/key and make-equal/key these are not combinators.

#### Usage

`(import sort-combinators)`

#### Examples

```(group/key identity '(1 2 3 3 4 4 4)) ;=> ((1) (2) (3 3) (4 4 4))

(group/key car '((a 1) (a 2) (b 1)))  ;=> '(((a 1) (a 2)) ((b 1)))

(sort '(("a" . 1) ("z" . 3) ("b" . 2)) (make-less-than/key first string-ci<?)) ;=> (("a" . 1) ("b" . 2) ("z" . 3))```

#### group-by

[procedure] (group-by FUNC [EQUALITY equal?]) => procedure

Returns a procedure that takes a list and groups the elements by some key attribute. Uses the single-argument FUNC to retrieve key values & the EQUALITY function to compare them.

#### group/key

[procedure] (group/key FUNC LYST [EQUALITY equal?])

Groups a LYST of elements by some key attribute. Uses the single-argument FUNC to retrieve key values & the EQUALITY function to compare them.

The LYST must be in sorted order with respect to the key!

Returns a list of grouped elements.

#### make-less-than/key

[procedure] (make-less-than/key FUNC [LESS-THAN <]) => {{procedure/2}}

Returns a two-argument procedure that uses the single-argument FUNC to retrieve key values & the two-argument LESS-THAN procedure to compare them.

#### make-equal/key

[procedure] (make-equal/key FUNC [EQUAL =]) => {{procedure/2}}

Returns a two-argument procedure that uses the single-argument FUNC to retrieve key values & the two-argument EQUAL procedure to compare them.

### Logical Combinators

#### Usage

`(import logical-combinators)`

#### andf

[procedure] (andf OBJECT...)

Eager version of and.

Returns last (not #f) OBJECT when all OBJECT... are (not #f), #f otherwise.

#### orf

[procedure] (orf OBJECT...)

Eager version of or.

Returns first (not #f) OBJECT, #f otherwise.

### Uni Combinators

C is a function.

F, G and H are function.

#### Usage

`(import uni-combinators)`

#### uni

[procedure] (uni C F) => procedure

Returns (lambda (X) (C (F X))).

#### uni2

[procedure] (uni2 C F) => procedure

Returns (lambda (X Y) (C (F X Y))).

#### uni3

[procedure] (uni3 C F) => procedure

Returns (lambda (X Y Z) (C (F X Y Z))).

#### uni-each

[procedure] (uni-each C F) => procedure

Same as uni.

#### uni-all

[procedure] (uni-all C F) => procedure

Returns (lambda XS (C (apply F XS))).

### Bi Combinators

#### Usage

`(import bi-combinators)`

#### bi

[procedure] (bi C F G) => procedure

Returns (lambda (X) (C (F X) (G X))).

#### bi2

[procedure] (bi2 C F G) => procedure

Returns (lambda (X Y) (C (F X Y) (G X Y))).

#### bi3

[procedure] (bi3 C F G) => procedure

Returns (lambda (X Y Z) (C (F X Y Z) (G X Y Z))).

#### bi-each

[procedure] (bi-each C F) => procedure

Returns (lambda (X Y) (C (F X) (F Y))).

#### bi-all

[procedure] (bi-all C F G) => procedure

Returns (lambda XS (C (apply F XS) (apply G XS))).

### Tri Combinators

#### Usage

`(import tri-combinators)`

#### tri

[procedure] (tri C F G H) => procedure

Returns (lambda (X) (C (F X) (G X) (H X))).

#### tri2

[procedure] (tri2 C F G H) => procedure

Returns (lambda (X Y) (C (F X Y) (G X Y) (H X Y))).

#### tri3

[procedure] (tri3 C F G H) => procedure

Returns (lambda (X Y Z) (C (F X Y Z) (G X Y Z) (H X Y Z))).

#### tri-each

[procedure] (tri-each C F) => procedure

Returns (lambda (X Y Z) (C (F X) (F Y) (F Z))).

#### tri-all

[procedure] (tri-all C F G H) => procedure

Returns (lambda XS (C (apply F XS) (apply G XS) (apply H XS))).

### Stack Combinators

These treat the argument list as a FORTH-like stack.

The utility is probably low.

#### Usage

`(import stack-combinators)`

C is a function.

F, G and H are function.

X, Y and Z are object.

#### uni

[procedure] (uni X F C) => procedure

Returns the result of (C (F X)).

[procedure] (uni F C) => {{procedure/1}}
[procedure] (uni C) => {{procedure/1}}
[procedure] (uni) => {{procedure/1}}

Returns a curried procedure.

#### uni2

[procedure] (uni2 X Y F C) => procedure

Returns the result of (C (F X Y)).

[procedure] (uni2 F C) => {{procedure/2}}
[procedure] (uni2 C) => {{procedure/1}}
[procedure] (uni2) => {{procedure/1}}

Returns a curried procedure.

#### uni3

[procedure] (uni3 X Y Z F C) => procedure

Returns the result of (C (F X Y Z)).

[procedure] (uni3 F C) => {{procedure/3}}
[procedure] (uni3 C) => {{procedure/1}}
[procedure] (uni3) => {{procedure/1}}

Returns a curried procedure.

#### uni@

[procedure] (uni@ X F C) => procedure

Returns the result of (C (F X)).

[procedure] (uni@ F C) => {{procedure/1}}

Returns a curried procedure.

#### bi

[procedure] (bi X F G C) => procedure

Returns the result of (C (F X) (G X)).

[procedure] (bi F G C) => {{procedure/1}}
[procedure] (bi F G) => {{procedure/1}}
[procedure] (bi C) => {{procedure/2}}
[procedure] (bi) => {{procedure/1}}

Returns a curried procedure.

#### bi2

[procedure] (bi2 X Y F G C) => procedure

Returns the result of (C (F X Y) (G X Y)).

[procedure] (bi2 F G C) => {{procedure/2}}
[procedure] (bi2 F G) => {{procedure/1}}
[procedure] (bi2 C) => {{procedure/2}}
[procedure] (bi2) => {{procedure/1}}

Returns a curried procedure.

#### bi3

[procedure] (bi3 X Y Z F G C) => procedure

Returns the result of (C (F X Y Z) (G X Y Z)).

[procedure] (bi3 F G C) => {{procedure/3}}
[procedure] (bi3 F G) => {{procedure/1}}
[procedure] (bi3 C) => {{procedure/2}}
[procedure] (bi3) => {{procedure/1}}

Returns a curried procedure.

#### bi@

[procedure] (bi@ X Y F C) => procedure

Returns the result of (C (F X) (F Y)).

[procedure] (bi@ F C) => {{procedure/2}}

Returns a curried procedure.

#### tri

[procedure] (tri X F G H C) => procedure

Returns the result of (C (F X) (G X) (H X)).

[procedure] (tri F G H C) => {{procedure/1}}
[procedure] (tri F G H) => {{procedure/1}}
[procedure] (tri C) => {{procedure/3}}
[procedure] (tri) => {{procedure/1}}

Returns a curried procedure.

#### tri2

[procedure] (tri2 X Y F G H C) => procedure

Returns the result of (C (F X Y) (G X Y) (H X Y)).

[procedure] (tri2 F G H C) => {{procedure/2}}
[procedure] (tri2 F G H) => {{procedure/1}}
[procedure] (tri2 C) => {{procedure/3}}
[procedure] (tri2) => {{procedure/1}}

Returns a curried procedure.

#### tri3

[procedure] (tri3 X Y Z F G H C) => procedure

Returns the result of (C (F X Y Z) (G X Y Z) (H X Y Z)).

[procedure] (tri3 F G H C) => {{procedure/3}}
[procedure] (tri3 F G H) => {{procedure/1}}
[procedure] (tri3 C) => {{procedure/3}}
[procedure] (tri3) => {{procedure/1}}

Returns a curried procedure.

#### tri@

[procedure] (tri@ X Y Z F C) => procedure

Returns the result of (C (F X) (F Y) (F Z)).

[procedure] (tri@ F C) => {{procedure/3}}

Returns a curried procedure.

#### dip

[procedure] (dip X Y F C) => procedure

Returns the result of (C (F X) Y).

[procedure] (dip F C) => {{procedure/2}}

Returns a curried procedure.

#### dup

[procedure] (dup X C) => procedure

Returns the result of (C X X).

[procedure] (dup C) => {{procedure/1}}

Returns a curried procedure.

#### dupd

[procedure] (dupd X Y C) => procedure

Returns the result of (C X X Y).

[procedure] (dupd C) => {{procedure/2}}

Returns a curried procedure.

#### swap

[procedure] (swap X Y C) => procedure

Returns the result of (C Y X).

[procedure] (swap C) => {{procedure/2}}

Returns a curried procedure.

#### drop

[procedure] (drop X C) => procedure

Returns the result of (C).

[procedure] (drop C) => {{procedure/1}}

Returns a curried procedure.

#### drop/2

[procedure] (drop/2 X Y C) => procedure

Returns the result of (C X).

[procedure] (drop/2 C) => {{procedure/2}}

Returns a curried procedure.

## Notes

• Inspired by e-mail conversations with Graham Fawcett in Feb '08.
• The procedures left-section and right-section from Philip L. Bewig.

Kon Lovett

## Repository

This egg is hosted on the CHICKEN Subversion repository:

https://anonymous@code.call-cc.org/svn/chicken-eggs/release/5/combinators

If you want to check out the source code repository of this egg and you are not familiar with Subversion, see this page.

1.2.0