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56#lang racket/base
(require racket/match)
(provide
read-env)
(define vardef-re
#rx"(?m:([^=]+)=(.*))\n?")
(define (read-env-var in)
(define-values (line col pos)
(port-next-location in))
(match (regexp-match vardef-re in)
[#f
(if (and line col)
(error 'read-env-var "invalid variable definition at ~a:~a" line col)
(error 'read-env-var "invalid variable definition at pos ~a" pos))]
[(list _ name value)
(values name value)]))
(define (read-env [in (current-input-port)])
(let loop ([vars (hash)])
(match (peek-char in)
[(? eof-object?) vars]
[#\#
(read-line in)
(loop vars)]
[_
(define-values (name value)
(read-env-var in))
(loop (hash-set vars name value))])))
(module+ test
(require rackunit)
(check-equal?
(read-env (open-input-string "A=42"))
(hash #"A" #"42"))
(check-equal?
(read-env (open-input-string #<<ENV
A=42
B=20
# a comment
A=1
ENV
))
(hash #"A" #"1"
#"B" #"20")))