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(in-package :parser-combinators)
;;; emulating monads... did I even understand those?
;;; bind :: Parser a -> (a -> Parser b) -> Parser b
;;; (parser-tree1 function-from-tree1-to-parser-tree2)=>parser-tree2
;;; p ‘bind‘ f = \inp -> concat [f v inp’ | (v,inp’) <- p inp]
;;; (bind p f inp)=(concat list-comprehension)
(defun execute-bind (inp parser parser-promise-generator) ;return continuation function
(let ((p-parse-result (funcall parser inp))
(q-parse-result nil))
#'(lambda ()
(let ((result nil))
(iter (when q-parse-result (setf result (next-result q-parse-result)))
(until (or result
(and (null p-parse-result)
(null q-parse-result))))
(unless result
(setf q-parse-result
(let ((p-next-result
(next-result p-parse-result)))
(if p-next-result
(let ((v (tree-of p-next-result))
(inp-prime (suffix-of p-next-result)))
(funcall (force (funcall parser-promise-generator v)) inp-prime))
(setf p-parse-result nil))))))
result))))
(defmacro bind (parser-promise parser-promise-generator) ; results in parser-promise
`(delay
(let ((parser-promise ,parser-promise)
(parser-promise-generator ,parser-promise-generator))
#'(lambda (inp)
(make-instance 'parse-result
:continuation
(execute-bind inp
(force parser-promise)
parser-promise-generator))))))
(defun execute-choice (inp parser1 parser2)
(let ((result1 (funcall parser1 inp))
(result2 nil))
#'(lambda ()
(cond (result1
(let ((result (next-result result1)))
(unless result
(setf result1 nil)
(setf result2 (funcall parser2 inp))
(setf result (next-result result2)))
result))
(result2
(let ((result (next-result result2)))
(unless result
(setf result2 nil)
result)))
(t nil)))))
(defmacro choice (parser1-promise parser2-promise)
"Combinator: all alternatives from two parsers"
`(delay
(let ((parser1-promise ,parser1-promise)
(parser2-promise ,parser2-promise))
#'(lambda (inp)
(make-instance 'parse-result
:continuation
(execute-choice inp (force parser1-promise) (force parser2-promise)))))))
(defmacro choice1 (parser1-promise parser2-promise)
"Combinator: one alternative from two parsers"
`(delay
(let ((parser1-promise ,parser1-promise)
(parser2-promise ,parser2-promise))
#'(lambda (inp)
(let ((parser1-promise parser1-promise)
(parser2-promise parser2-promise)
(is-unread t))
(make-instance 'parse-result
:continuation
#'(lambda ()
(when is-unread
(setf is-unread nil)
(let ((result (funcall (execute-choice inp
(force parser1-promise)
(force parser2-promise)))))
(setf parser1-promise nil parser2-promise nil)
result)))))))))
(defmacro choices (&rest parser-promise-list)
"Combinator: all alternatives from multiple parsers"
(if (cdr parser-promise-list)
`(choice ,(car parser-promise-list)
(choices ,@(cdr parser-promise-list)))
(car parser-promise-list)))
(defmacro choices1 (&rest parser-promise-list)
"Combinator: one alternative from multiple parsers"
`(delay
(let ((parser-promise-list (list ,@parser-promise-list)))
#'(lambda (inp)
(let ((parser-promise-list parser-promise-list)
(is-unread t))
(make-instance 'parse-result
:continuation
#'(lambda ()
(when is-unread
(setf is-unread t)
(iter (for p in parser-promise-list)
(for result = (next-result (funcall (force p) inp)))
(finding (make-instance 'parse-result
:top-results (list (car result-list)))
such-that result)
(finally (setf parser-promise-list nil)))))))))))
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