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CSV

Overview

Eta ships a native CSV subsystem backed by vincentlaucsb/csv-parser. The public API is in std.csv, with optional bridge helpers in std.fact_table.

Key properties:

Correct RFC4180 quoting and escaped quotes.
CRLF/LF and UTF-8 BOM handling.
Streaming reads (csv:fold, csv:for-each) for constant-memory ingestion.
Native writer with configurable delimiter, quote character, and quote policy.
Typed row reads with null-token handling.

Quick Start

(import std.csv)

;; Reader
(define r (csv:open-reader "trades.csv"))
(define cols (csv:columns r))
(define rec  (csv:read-record r))
(csv:close r)

;; Writer
(define w (csv:open-writer "out.csv" :column-names '(symbol qty price)))
(csv:write-record w '((symbol . "AAPL") (qty . 100) (price . 150.25))
                  '(symbol qty price))
(csv:close w)

std.csv API

Reader:

csv:open-reader
csv:reader-from-string
csv:columns
csv:read-row
csv:read-record
csv:read-typed-row
csv:reader?
csv:close

Streaming helpers:

csv:fold
csv:for-each
csv:collect
csv:load-file

Writer:

csv:open-writer
csv:write-row
csv:write-record
csv:flush
csv:writer?
csv:save-file

Options

Accepted keyword options (symbols or strings, with or without leading :):

Key	Reader	Writer	Default
`delimiter`	yes	yes	`#\,`
`quote`	yes	yes	`#\"`
`header`	yes	yes	`#t`
`header-row`	yes	no	`0`
`trim`	yes	no	`#t`
`comment`	yes	no	`#f`
`column-names`	yes	yes	`#f`
`null-tokens`	yes	no	`("" "NA" "NaN")`
`quote-policy`	no	yes	`'minimal`
`infer-types?`	fact-table-load only	no	`#t`

Writer quote-policy values:

'minimal
'all
'non-numeric
'none

Typed Rows

csv:read-typed-row parses each cell as:

nil if it matches a null token.
Fixnum if integer parse succeeds (from_chars).
Flonum if floating parse succeeds (from_chars).
String otherwise.

This parsing is locale-independent. Example: 1,5 stays a string unless the CSV delimiter is set so the cell text itself is a valid numeric form.

FactTable Bridge

std.fact_table provides:

fact-table-load-csv
fact-table-save-csv

Examples:

(import std.fact_table)

(define ft (fact-table-load-csv "trades.csv" :infer-types? #t))
(fact-table-save-csv ft "trades-out.csv")

fact-table-load-csv supports the reader options plus :infer-types?. When :infer-types? #f, numeric-looking cells are kept as strings.

Threading Note

CSV reader and writer handles are stateful heap objects and are not safe for concurrent mutation from multiple Eta threads.