servant-dhall's Introduction

servant-dhall - Servant Dhall bindings

Note: accepting dhall expressions from untrusted sources is a security risk.

Example

Run example

cabal new-run example run

Get

% curl 'localhost:8000/get'
[ +1, +2, +3, +4, +5, +6, +7, +8, +9, +10 ] : List Integer

Post

% curl -D - -X POST -H 'Content-Type: application/x-dhall' --data-raw '[+10,+20]' 'localhost:8000/post'
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Date: Wed, 13 Jun 2018 10:41:07 GMT
Server: Warp/3.2.22
Content-Type: application/x-dhall

[ +11, +21 ] : List Integer

Error case: Unexpected type

% curl -D - -X POST -H 'Content-Type: application/x-dhall' --data-raw '[10]' 'localhost:8000/post'
curl: (7) Failed to connect to localhost port 8000: Connection refused
[FL973] ~/Documents/public-haskell/servant-dhall % curl -D - -X POST -H 'Content-Type: application/x-dhall' --data-raw '[10]' 'localhost:8000/post'
HTTP/1.1 400 Bad Request
Transfer-Encoding: chunked
Date: Wed, 13 Jun 2018 10:45:39 GMT
Server: Warp/3.2.22

Expected and actual types don't match : List Integer /= List Natural

Error case: Type error

% curl -D - -X POST -H 'Content-Type: application/x-dhall' --data-raw 'True && +1' 'localhost:8000/post'
HTTP/1.1 400 Bad Request
Transfer-Encoding: chunked
Date: Wed, 13 Jun 2018 10:51:52 GMT
Server: Warp/3.2.22

Type error: 
Error: ❰&&❱ only works on ❰Bool❱s

True && +1

(input):1:1

Error case: Imports

As deserialisation is done in pure context type-checking Dhall expressions with imports is not possible.

% curl -D - -X POST -H 'Content-Type: application/x-dhall' --data-raw 'http://example.com/dhall' 'localhost:8000/post'
HTTP/1.1 400 Bad Request
Transfer-Encoding: chunked
Date: Wed, 13 Jun 2018 10:53:52 GMT
Server: Warp/3.2.22

Import found: http://example.com/dhall

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