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;; csvread.lsp -- csv file reader
;;
;; Roger B. Dannenberg
;; June 2022
;; CSV file reader
;; Rows are terminated by newlines, but columns are SEPARATED by commas.
;; Therefore, every row has at least one column, which may be empty.
;; Empty columns are represented by NIL.
;; Non-empty columns are converted to FIXNUM, FLONUM, or STRING, etc.
;; Fields separated by commas are read with XLisp's READ function, but
;; when a symbol is read, the original field is trimmed of leading or
;; trailing whitespace and returned. This preserves lower-case letters.
;;
;; Limitation: if a field contains a number or quoted string followed
;; by space followed by non-space, it will be parsed as a number or
;; string, and the remainder will be ignored.
;;
;; Feature: if a field contains an array, e.g. #(1 2 3), it will be
;; parsed as an array, provided the representation has no comma or
;; double-quote character. #("," "," ",") will probably raise an error.
;;
;; If there are characters beyond the last newline, a final
;; newline is assumed and the characters are interpreted as the last row.
;; read a csv file. parameter is either a path or an open file
;; file is closed after reading.
;;
;; returns just the opened file, which you should pass to
;; csv-read-row() to get the next row.
;;
;; if all is true, csv-read returns list of all rows
;;
(defun csv-read (inf &optional all &aux filename)
(setf filename inf) ;; in case we need the original parameter
(cond ((stringp inf)
(setf inf (open inf))))
(cond ((not (filep inf))
(error (format nil "csv-read: could not get a file from ~A"
filename))))
;; return one row or all rows...
(if all
(prog (csv row)
process-row
(setf row (csv-read-row inf))
(if (null row) (return (reverse csv)))
;; add row to csv
(setf csv (cons row csv))
(go process-row))
;; if not all, just return the input file
inf))
;; read a single row (line) from CSV file
;; inf is opened file returned by csv-read()
;; returns one row or nil at end of file
;;
(defun csv-read-row(inf)
(prog* ((line (read-line inf))
(linelen (length line))
(index 0) (search-from 0)
col row comma-loc)
(cond ((not line)
(close inf)
(return nil)))
loop ;; accumulate fields into row
(cond ((setf comma-loc (string-search "," line :start search-from))
;; comma could be embedded in a string
(setf col (string-trim " " (subseq line index comma-loc)))
(cond ((unclosed-string col)
(setf search-from (1+ comma-loc))
(go loop))) ;; search for next comma; this one is quoted
(setf row (add-token-to-row col row)
index (1+ comma-loc))
(setf search-from index)
(go loop)))
(setf row (add-token-to-row (subseq line index linelen) row)) ;; last col
(return (reverse row))))
;; see if we got a partial string: begins with double-quote ("), no match yet
(defun unclosed-string (str)
(prog ((index 1) (len (length str)) (inquote t) (escaped nil) ch)
(if (or (= len 0) (not (eq (char str 0) #\"))) (return nil))
;; if we reach here, str[index] is within open quote
scan
(if (= index len) (return inquote))
(setf ch (char str index))
(cond (escaped (setf escaped nil)) ;; any char can be escaped
((eq ch #\\) (setf escaped t))
((eq ch #\")
(setf inquote nil)
(setf index (1- len)))) ;; found end-of-string, forces return nil
(setf index (1+ index))
(go scan)))
(defun add-token-to-row (token row)
(let (col)
(setf col (read (make-string-input-stream token)))
;; unquoted string may convert to a symbol, but we want the original
;; string, but with spaces trimmed, e.g. "..., xyz ,..." -> "xyz"
(cond ((eq (type-of col) 'SYMBOL)
(setf col (string-trim " " token))))
(cons col row)))
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