curry-compose-reader-macros

2018-07-11

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 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)

Load CURRY-COMPOSE-READER-MACROS at the REPL with the following

(ql:quickload :curry-compose-reader-macros)
(ql:quickload :named-readtables)
(use-package 'named-readtables)
(in-readtable :curry-compose-reader-macros)

Use CURRY-COMPOSE-READER-MACROS in source by adding NAMED-READTABLES and CURRY-COMPOSE-READER-MACROS to your ASDF file and package and then including the following in source files which use these reader macros.

(in-readtable :curry-compose-reader-macros)

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