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Weaver is a small extensible configuration pre-processing library written in Clojure(Script) and targetting both the JVM and Lumo. The main functionality is process and associated functions which are backed by the process-node multimethod. There are some processors provided, which are discussed below, but since process-node is a multimethod, it can be extended however you wish.


This Library is still in VERY early stages of development and is highly opinionated to my personal use case. I will do my best to review and accept any PRs, but I will only develop features that are relevant to my use cases for now.

There are some interop and utility functions included. Do not depend on any of these. They are purely for convenience and use inside the library. The API may change or functions may be removed at my discretion.


  • Use errors and allow user to exit process if needed
  • env is borked




This transforms into the provided key in your config (passed in on the context map). Will error and exit if the key isn't found. Equivalent to [:config/get! <key>]

[:config/<get|get-in|get!|get-in!> <key-or-path-vec> <optional-default-value>]

get and get! expect keys, get-in and get-in! expect path vectors.

get and get-in optionally take a default value and fall back to nil if one isn't provided, get! and get-in! will error if the value is absent in the config.


General purpose processors that access arbritrary paths into the context map

:ctx/get-in-resource & ctx/get-in-resource!

Takes :resource-id and :path (non ! optionally takes :default) Behaves like get-in where :resource-id is the top level context key you wish to access, and :path is the path to the value you'd like to access. ! indicates that the processor will error if no value is found.


Takes :function-id and :args. :function-id is the top level context key that points to the function to be called, and :args are the arguments to be passed.



This will look up an environment variable and error out if it isn't found.

[:env/<get|get!> <case-sensitive-env-variable> <optional-default-value>]

Same behaviour as in config, but accesses environment instead.



Looks up the function in either the default function lookup or a :function-lookup passed in via the context map. Note that the lookup uses the namespaced keywords, so make sure that any provided :function-lookup is a namespaced map (i.e. #:fn{:first first}) Defaults currently contains: str, =, <, >, <=, >=



Takes :string and :args. Calls clojure.pprint/cl-format to process :string as as format-string with :args as args.



Returns the short hash of HEAD



Takes :long. returns either a clj-time object or a cljs-time object depending on the runtime. Intended for use by other processors.


Takes :time and optional :time-zone and :format-string. Formats time according to time-zone and format-string. Defaults to "UTC" and "yyyy-MM-ddTHH:mm:ss.SSSZZZ". Template wide defaults can be specified in the context at :time-zone and :format-string.


Generally applicable processors


{:weaver.processor/id :weaver/drop-nils
 :coll [list of vals or processors]}
[:weaver/drop-nils nilable-processor1 nilable-processor2 nilable-processor3]


{:weaver.processor/id :weaver/if
 :pred [some processor]
 :if [some processor for truthy case]
 :else [some processor for falsey case]}
[:weaver/if :pred :if :else]


{:weaver.processor/id :weaver/when
 :pred [some processor]
 :val [some processor if truthy]}
[:weaver/when :pred :val]


{:weaver.processor/id :weaver/cond
 :clauses [pred1 processor1 pred2 processor2 ...]}
[:weaver/cond pred1 processor1 :else processor-else]

Development mode

To start the Figwheel compiler, navigate to the project folder and run the following command in the terminal:

lein figwheel

Test from the repl

Building for production


NOTE: npm repo will be weaver-cljs