simple flex score function for nyxt

flex.lisp

(in-package :prompter)
(defun score-suggestion-string (input suggestion-string)
  (let ((i 0)
        (score 0.0))
    (declare (optimize (speed 3) (safety 0))
             (type single-float score) (type fixnum i)
             (type (simple-array character) input suggestion-string))
    (loop for c across input do
      (let ((next (position c suggestion-string :start i :test 'eq)))
        (if next
            (progn
              (incf score (/ 1.0 (1+ next)))
              (setq i next))
            (return))))
    score))

flex2.lisp

(in-package :prompter)
(defvar word-separator '(#\  #\Tab))
(defun score-suggestion-string (input suggestion-string)
  (let ((i 0)
        (score 0.0))
    (declare (optimize (speed 3) (safety 0))
             (type single-float score) (type fixnum i)
             (type (simple-array character) input suggestion-string))
    (loop for c across input do
      (if (member c word-separator :test 'eq)
          (setq i 0)
          (let ((next (position c suggestion-string :start i :test 'eq)))
            (if next
                (progn
                  (incf score (/ 1.0 (1+ next)))
                  (setq i next))
                (return)))))
    (let ((next (position-if (lambda (c) (member c word-separator :test 'eq))
                             suggestion-string :start i)))
      (when next
        (incf score (/ 1.0 (1+ next)))))
    score))

flex3.lisp

(in-package :prompter)
(defvar word-separator '(#\  #\Tab))
(defun score-suggestion-string (input suggestion-string)
  (let ((i 0)
        (score 0.0)
        (lastchar #\ ))
    (declare (optimize (speed 3) (safety 0))
             (type single-float score) (type fixnum i) (type character lastchar)
             (type (simple-array character) input suggestion-string))

    (flet ((word-end ()
             ;; bonus for word ending early (shorter words at the beginning wins)
             (let ((next (position-if (lambda (c) (member c word-separator :test 'eq))
                                      suggestion-string :start i)))
               (unless next (setq next (length suggestion-string)))
               (incf score (/ 1.0 (1+ next)))
               (setq i 0))))
      ;; flex match, with higher weight for the beginning
      (loop for c across input do
        (if (member c word-separator :test 'eq)
            (word-end)
            (let ((next (position c suggestion-string :start i :test 'eq)))
              (if next
                  (progn
                    ;; bonus for continuous match
                    (when (and (> next 0)
                               (eq (aref suggestion-string (1- next)) lastchar))
                      (incf score 0.1))
                    (incf score (/ 1.0 (1+ next)))
                    (setq i next lastchar c))
                  (return)))))
      (when (> i 0) (word-end)))
    score))