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@@ -1,3 +1,6 @@ |
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;;;; A program to print out the current real-time status of the computer parking terminal equipped |
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;;;; parking garages in the city of Linköping using the municipal open data API. |
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(import medea) |
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(import http-client) |
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(import srfi-1) |
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@@ -26,9 +29,11 @@ |
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(define (default b a) |
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(if a a b)) |
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;;; Return the value for a given key in an association list, or #f if it doesn't exist. |
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(define value |
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(compose (curry perhaps cdr) assoc)) |
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;;; Return the value for a given key in an association list, or a default value if it doesn't exist. |
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(define (value-with-default k v ln) |
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(default v (value k ln))) |
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@@ -42,6 +47,7 @@ |
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(list (car ln)) |
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(sort less-than? (filter (curry less-than? (car ln)) (cdr ln)))))) |
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;;; Sort using fn to extract a value for less-than? to compare for each element in ln. |
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(define (sort-via less-than? fn ln) |
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(sort (lambda (a b) |
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(less-than? (fn a) (fn b))) ln)) |
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@@ -55,37 +61,57 @@ |
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((symbol? a) (symbol->string a)) |
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((number? a) (number->string a)) |
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((char? a) (string a)))) |
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;;; Given a list of either symbols or strings and an association list: |
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;;; look up every symbol from left to right in the association list and replace it with the value found |
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;;; then concatenate the resulting list of strings |
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(define (format-assoc statement ln) |
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(apply string-append |
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(map (curry2 upon symbol? (compose ->string (curry (flip value) ln))) statement))) |
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;;; Get data from a uri and parse it as json. |
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(define (simple-json-request uri) |
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(with-input-from-request uri #f read-json)) |
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;;; The API key is an alphanumeric string of length 32 |
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;;; The Linköping municipal open data API key generator portal is located at http://opendata.linkoping.se |
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(define parking-key |
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(with-input-from-file "key-parking" read-line)) |
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;;; Get a list of parking lots with various metadata from the municipal servers. |
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;;; It should be noted that this API is both glitchy and bugged. Two bugs have been noted: |
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;;; the timestamp parameter, which is supposed to give you a list of lots changed since a given UNIX timestamp |
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;;; instead results in giving you every lot up until a timestamp of under one hour into the future, after which |
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;;; it returns nothing. This bug may be platform related; as of this writing the server system providing the API |
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;;; runs on Windows Server 2016 via IIS 10.0. |
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;;; The second bug involves returning only partial data upon request - no pattern to this bug has been observed. |
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(define (get-parking-lots) |
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(value 'parkingareanewlist |
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(simple-json-request (string-append "http://parkering.linkoping.se/Parkeringsdata/ParkeringsdataV1.svc/GetParkeringsYtaList/" parking-key "/0")))) |
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;;; Only lots tracked by parking lot computer terminals have the parkingspacesavailable key. |
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(define (computerized? lot) |
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(has-key? 'parkingspacesavailable lot)) |
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;;; The handicap lots are tracked as separate lots with duplicate names in the data set. |
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(define (only-has-handicap-spots? lot) |
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(equal? '(4) (value 'parkingtypes lot))) |
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;;; Electric car lots have a separate lot type, and the downtown parking garages have spaces with charging stations |
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;;; but they are not implemented in the data set. |
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(define (electric-car-lot? lot) |
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(member? 3 (value 'parkingtypes lot))) |
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(define (main) |
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;; We want members to be parsed as lowercase symbols, and arrays to be parsed as lists. |
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;; This is not a legal way to parse json, which requires case-sensitive members |
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;; but makes for neater scheme code. |
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(json-parsers (append `((member . ,(lambda (k v) |
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(cons (string->symbol (string-downcase k)) v))) |
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(array . ,identity)) (json-parsers))) |
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(display-newline "Parking spaces available:") |
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(map (compose display-newline (curry format-assoc '(name ": " parkingspacesavailable "/" parkingspaces))) |
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(sort-via string-ci<? (curry value 'name) |
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(sort-via string-ci<? (curry value 'name) |
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(filter (conjoin computerized? (complement only-has-handicap-spots?)) (get-parking-lots))))) |
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(main) |