• egg

combinators

Combinators grab-bag.

Documentation

Section Combinators

Usage

`(require-extension 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

`(require-extension 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

`(require-extension 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

`(require-extension 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

`(require-extension 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

`(require-extension 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

`(require-extension 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

1.2.0