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(in-package #:parser)
(defun run (p input)
(let ((r (funcall p input)))
(if (parsing-p r)
(parsing-tree r)
(input::generate-report (failure-place r) (failure-message r)))))
(defstruct parsing
tree
left)
(defstruct failure
place
message)
(defun new (tree)
(lambda (input)
(make-parsing :tree tree :left input)))
(defun bind (p f)
(lambda (input)
(let ((r (funcall p input)))
(if (parsing-p r)
(funcall (funcall f (parsing-tree r)) (parsing-left r))
r))))
(defun fail (&optional (message "Unknown error."))
(lambda (input)
(make-failure :place input :message message)))
(defun either (first-parser &rest other-parsers)
(lambda (input)
(labels ((either-rec (body)
(if (cdr body)
(let ((r (funcall (car body) input)))
(if (parsing-p r)
r
(either-rec (cdr body))))
(funcall (car body) input))))
(either-rec (cons first-parser other-parsers)))))
(defun unit (&optional (predicate #'characterp))
(lambda (input)
(if (input::has-data? input)
(let ((c (input::element input)))
(if (funcall predicate c)
(make-parsing :tree c :left (input::advance input))
(make-failure :place input :message "Predicate not satisfied.")))
(make-failure :place input :message "Reached end of input."))))
(defmacro comp (bindings &body body)
(if (null bindings)
`(new (progn ,@body))
(let ((v (first (car bindings)))
(p (second (car bindings))))
`(bind ,p (lambda (,v) (comp ,(cdr bindings) ,@body))))))
(defparameter nothing
(new nil))
(defun zero-or-one (p)
(either p nothing))
(defun zero-or-more (p)
(either (comp ((x p)
(xs (zero-or-more p)))
(cons x xs))
nothing))
(defun one-or-more (p)
(comp ((x p)
(xs (zero-or-more p)))
(cons x xs)))
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