curry-compose-reader-macros

2017-01-24

CURRY-COMPOSE-READER-MACROS

Reader macros for concise expression of function partial application and composition.

These reader macros expand into the curry, rcurry and compose functions from the Alexandria library. The contents of curly brackets are curried and the contents of square brackets are composed. The _ symbol inside curly brackets changes the order of arguments with rcurry.

The following examples demonstrate usage.

;; partial application `curry'
(mapcar {+ 1} '(1 2 3 4)) ; => (2 3 4 5)

;; alternate order of arguments `rcurry'
(mapcar {- _ 1} '(1 2 3 4)) ; => (0 1 2 3)

;; function composition
(mapcar [#'list {* 2}] '(1 2 3 4)) ; => ((2) (4) (6) (8))

Additionally, if optional utf8 support is enabled, special brackets may be used to split arguments amongst a list of functions and collect the results. The first element of the ??-delimited list is the "join" function. Incoming arguments are split out to the remaining functions in the ??-delimited list, and their results are then passed to the join function.

;; function split and join
(mapcar ?list {* 2} {* 3}? '(1 2 3 4)) ; => ((2 3) (4 6) (6 9) (8 12))
(mapcar ?and {< 2} #'evenp? '(1 2 3 4)) ; => (NIL NIL NIL T)
(mapcar ?+ {* 2} {- _ 1}? '(1 2 3 4)) ; => (2 5 8 11)

enable-curry-compose-reader-macros is a macro which wraps itself in eval-when to ensure that reader macros are defined for both compilation and execution.

(enable-curry-compose-reader-macros)

Or to load utf8 support as well (which is probably going too far).

(enable-curry-compose-reader-macros :include-utf8)

Emacs users may easily treat {}'s, []'s and ??'s as parenthesis for paredit commands and SEXP movement with the following configuration.

;; Syntax table
(modify-syntax-entry ?\[ "(]" lisp-mode-syntax-table)
(modify-syntax-entry ?\] ")[" lisp-mode-syntax-table)
(modify-syntax-entry ?\{ "(}" lisp-mode-syntax-table)
(modify-syntax-entry ?\} "){" lisp-mode-syntax-table)
;; optional UTF8 characters
(modify-syntax-entry ?\? "(?" lisp-mode-syntax-table)
(modify-syntax-entry ?\? ")?" lisp-mode-syntax-table)

;; Paredit keys
(eval-after-load "paredit"
  '(progn
    (define-key paredit-mode-map "[" 'paredit-open-parenthesis)
    (define-key paredit-mode-map "]" 'paredit-close-parenthesis)
    (define-key paredit-mode-map "(" 'paredit-open-bracket)
    (define-key paredit-mode-map ")" 'paredit-close-bracket)
    (define-key paredit-mode-map "{" 'paredit-open-curly)
    (define-key paredit-mode-map "}" 'paredit-close-curly)))
Author
Eric Schulte <schulte.eric@gmail.com>
License
Public Domain