1 Introduction
2 Reader Specs
3 Making Reader Makers
4 Making Readers
5 High-Level Conveniences
6 Converting CSV to SXML
7 History
8 Legal
Version: 0.10

csv: Comma-Separated Value (CSV) Utilities in Scheme

Neil Van Dyke

License: LGPL 3   Web: http://www.neilvandyke.org/csv-scheme/

 (require (planet neil/csv:1:6))

1 Introduction

The csv Scheme library provides utilities for reading various kinds of what are commonly known as “comma-separated value” (CSV) files. Since there is no standard CSV format, this library permits CSV readers to be constructed from a specification of the peculiarities of a given variant. A default reader handles the majority of formats.

One of the main uses of this library is to import data from old crusty legacy applications into Scheme for data conversion and other processing. To that end, this library includes various conveniences for iterating over parsed CSV rows, and for converting CSV input to the SXML 3.0 Scheme XML format.

This library requires R5RS, SRFI-6, SRFI-23, and an integer->char procedure that accepts ASCII values.

Other implementations of some kind of CSV reading for Scheme include Gauche’s text.csv module, and Scsh’s record-reader and related procedures. This library intends to be portable and more comprehensive.

2 Reader Specs

CSV readers are constructed using reader specs, which are sets of attribute-value pairs, represented in Scheme as association lists keyed on symbols. Each attribute has a default value if not specified otherwise. The attributes are:

3 Making Reader Makers

CSV readers are procedures that are constructed dynamically to close over a particular CSV input and yield a parsed row value each time the procedure is applied. For efficiency reasons, the reader procedures are themselves constructed by another procedure, make-csv-reader-maker, for particular CSV reader specs.

(make-csv-reader-maker reader-spec)

Constructs a CSV reader constructor procedure from the reader-spec, with unspecified attributes having their default values.

For example, given the input file fruits.csv with the content:

apples  |  2 |  0.42

bananas | 20 | 13.69

a reader for the file’s apparent format can be constructed like:

  (define make-food-csv-reader
     '((separator-chars               #\|)
       (strip-leading-whitespace?  . #t)
       (strip-trailing-whitespace? . #t))))

The resulting make-food-csv-reader procedure accepts one argument, which is either an input port from which to read, or a string from which to read. Our example input file then can be be read by opening an input port on a file and using our new procedure to construct a reader on it:

  (define next-row
    (make-food-csv-reader (open-input-file "fruits.csv")))

This reader, next-row, can then be called repeatedly to yield a parsed representation of each subsequent row. The parsed format is a list of strings, one string for each column. The null list is yielded to indicate that all rows have already been yielded.

  (next-row) ==> ("apples" "2" "0.42")
  (next-row) ==> ("bananas" "20" "13.69")
  (next-row) ==> ()

4 Making Readers

In addition to being constructed from the result of make-csv-reader-maker, CSV readers can also be constructed using make-csv-reader.

(make-csv-reader in reader-spec)

Construct a CSV reader on the input in, which is an input port or a string. If reader-spec is given, and is not the null list, then a “one-shot” reader constructor is constructed with that spec and used. If reader-spec is not given, or is the null list, then the default CSV reader constructor is used. For example, the reader from the make-csv-reader-maker example could alternatively have been constructed like:

  (define next-row
     (open-input-file "fruits.csv")
     '((separator-chars               #\|)
       (strip-leading-whitespace?  . #t)
       (strip-trailing-whitespace? . #t))))

5 High-Level Conveniences

Several convenience procedures are provided for iterating over the CSV rows and for converting the CSV to a list.

To the dismay of some Scheme purists, each of these procedures accepts a reader-or-in argument, which can be a CSV reader, an input port, or a string. If not a CSV reader, then the default reader constructor is used. For example, all three of the following are equivalent:

  (csv->list                                     STRING)
  (csv->list (make-csv-reader                    STRING))
  (csv->list (make-csv-reader (open-input-string STRING)))

(csv-for-each proc reader-or-in)

Similar to Scheme’s for-each, applies proc, a procedure of one argument, to each parsed CSV row in series. reader-or-in is the CSV reader, input port, or string. The return value is undefined.

(csv-map proc reader-or-in)

Similar to Scheme’s map, applies proc, a procedure of one argument, to each parsed CSV row in series, and yields a list of the values of each application of proc, in order. reader-or-in is the CSV reader, input port, or string.

(csv->list reader-or-in)

Yields a list of CSV row lists from input reader-or-in, which is a CSV reader, input port, or string.

6 Converting CSV to SXML

The csv->sxml procedure can be used to convert CSV to SXML format, for processing with various XML tools.

(csv->sxml reader-or-in row-element col-elements)

Reads CSV from input reader-or-in (which is a CSV reader, input port, or string), and yields an SXML representation. If given, row-element is a symbol for the XML row element. If row-element is not given, the default is the symbol row. If given col-elements is a list of symbols for the XML column elements. If not given, or there are more columns in a row than given symbols, column element symbols are of the format col-n, where n is the column number (the first column being number 0, not 1).

For example, given a CSV-format file friends.csv that has the contents:

Binoche,Ste. Brune,33-1-2-3

Posey,Main St.,555-5309

Ryder,Cellblock 9,

with elements not given, the result is:

  (csv->sxml (open-input-file "friends.csv"))
   (row (col-0 "Binoche") (col-1 "Ste. Brune")  (col-2 "33-1-2-3"))
   (row (col-0 "Posey")   (col-1 "Main St.")    (col-2 "555-5309"))
   (row (col-0 "Ryder")   (col-1 "Cellblock 9") (col-2 "")))

With elements given, the result is like:

  (csv->sxml (open-input-file "friends.csv")
             '(name address phone))
  (*TOP* (friend (name    "Binoche")
                 (address "Ste. Brune")
                 (phone   "33-1-2-3"))
         (friend (name    "Posey")
                 (address "Main St.")
                 (phone   "555-5309"))
         (friend (name    "Ryder")
                 (address "Cellblock 9")
                 (phone   "")))

7 History

8 Legal

Copyright (c) 2004–2009 Neil Van Dyke. This program is Free Software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License (LGPL 3), or (at your option) any later version. This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. See http://www.gnu.org/licenses/ for details. For other licenses and consulting, please contact the author.