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+Nix builtins
+============
+
+Nix has a lot of built-in functions, some of which are accessible in
+the global scope, and some of which are only accessible through the
+global `builtins` attribute set.
+
+This document is an attempt to track all of these builtins, but
+without documenting their functionality.
+
+See also https://nixos.org/manual/nix/stable/expressions/builtins.html
+
+The `impl` column indicates implementation status in tvix:
+- implemented: "" (empty cell)
+- not yet implemented, but not blocked: `todo`
+- not yet implemented, but blocked by other prerequisites:
+  - `store`: awaiting eval<->store api(s)
+  - `context`: awaiting support for string contexts
+
+| name                          | global | arity | pure  | impl    |
+|-------------------------------|--------|-------|-------|---------|
+| abort                         | true   | 1     |       |         |
+| add                           | false  | 2     | true  |         |
+| addErrorContext               | false  | ?     |       | context |
+| all                           | false  | 2     | true  |         |
+| any                           | false  | 2     | true  |         |
+| appendContext                 | false  | ?     |       | context |
+| attrNames                     | false  | 1     | true  |         |
+| attrValues                    | false  |       | true  |         |
+| baseNameOf                    | true   |       |       |         |
+| bitAnd                        | false  |       |       |         |
+| bitOr                         | false  |       |       |         |
+| bitXor                        | false  |       |       |         |
+| builtins                      | true   |       |       |         |
+| catAttrs                      | false  |       |       |         |
+| compareVersions               | false  |       |       |         |
+| concatLists                   | false  |       |       |         |
+| concatMap                     | false  |       |       |         |
+| concatStringsSep              | false  |       |       |         |
+| currentSystem                 | false  |       |       |         |
+| currentTime                   | false  |       | false |         |
+| deepSeq                       | false  |       |       |         |
+| derivation                    | true   |       |       | store   |
+| derivationStrict              | true   |       |       | store   |
+| dirOf                         | true   |       |       |         |
+| div                           | false  |       |       |         |
+| elem                          | false  |       |       |         |
+| elemAt                        | false  |       |       |         |
+| false                         | true   |       |       |         |
+| fetchGit                      | true   |       |       | store   |
+| fetchMercurial                | true   |       |       | store   |
+| fetchTarball                  | true   |       |       | store   |
+| fetchurl                      | false  |       |       | store   |
+| filter                        | false  |       |       |         |
+| filterSource                  | false  |       |       | store   |
+| findFile                      | false  |       | false | todo    |
+| foldl'                        | false  |       |       |         |
+| fromJSON                      | false  |       |       |         |
+| fromTOML                      | true   |       |       |         |
+| functionArgs                  | false  |       |       |         |
+| genList                       | false  |       |       |         |
+| genericClosure                | false  |       |       | todo    |
+| getAttr                       | false  |       |       |         |
+| getContext                    | false  |       |       | context |
+| getEnv                        | false  |       | false |         |
+| hasAttr                       | false  |       |       |         |
+| hasContext                    | false  |       |       | context |
+| hashFile                      | false  |       | false | todo    |
+| hashString                    | false  |       |       | todo    |
+| head                          | false  |       |       |         |
+| import                        | true   |       |       |         |
+| intersectAttrs                | false  |       |       |         |
+| isAttrs                       | false  |       |       |         |
+| isBool                        | false  |       |       |         |
+| isFloat                       | false  |       |       |         |
+| isFunction                    | false  |       |       |         |
+| isInt                         | false  |       |       |         |
+| isList                        | false  |       |       |         |
+| isNull                        | true   |       |       |         |
+| isPath                        | false  |       |       |         |
+| isString                      | false  |       |       |         |
+| langVersion                   | false  |       |       |         |
+| length                        | false  |       |       |         |
+| lessThan                      | false  |       |       |         |
+| listToAttrs                   | false  |       |       |         |
+| map                           | true   |       |       |         |
+| mapAttrs                      | false  |       |       |         |
+| match                         | false  |       |       |         |
+| mul                           | false  |       |       |         |
+| nixPath                       | false  |       |       | todo    |
+| nixVersion                    | false  |       |       | todo    |
+| null                          | true   |       |       |         |
+| parseDrvName                  | false  |       |       |         |
+| partition                     | false  |       |       |         |
+| path                          | false  |       | sometimes | store |
+| pathExists                    | false  |       | false |         |
+| placeholder                   | true   |       |       | context |
+| readDir                       | false  |       | false |         |
+| readFile                      | false  |       | false |         |
+| removeAttrs                   | true   |       |       |         |
+| replaceStrings                | false  |       |       |         |
+| scopedImport                  | true   |       |       |         |
+| seq                           | false  |       |       |         |
+| sort                          | false  |       |       |         |
+| split                         | false  |       |       |         |
+| splitVersion                  | false  |       |       |         |
+| storeDir                      | false  |       |       | store   |
+| storePath                     | false  |       |       | store   |
+| stringLength                  | false  |       |       |         |
+| sub                           | false  |       |       |         |
+| substring                     | false  |       |       |         |
+| tail                          | false  |       |       |         |
+| throw                         | true   |       |       |         |
+| toFile                        | false  |       |       | store   |
+| toJSON                        | false  |       |       | todo    |
+| toPath                        | false  |       |       |         |
+| toString                      | true   |       |       |         |
+| toXML                         | false  |       |       | todo    |
+| trace                         | false  |       |       |         |
+| true                          | true   |       |       |         |
+| tryEval                       | false  |       |       |         |
+| typeOf                        | false  |       |       |         |
+| unsafeDiscardOutputDependency | false  |       |       | context |
+| unsafeDiscardStringContext    | false  |       |       | context |
+| unsafeGetAttrPos              | false  |       |       | todo    |
+| valueSize                     | false  |       |       | todo    |
+
+## Added after C++ Nix 2.3 (without Flakes enabled)
+
+| name          | global | arity | pure  | impl  |
+|---------------|--------|-------|-------|-------|
+| break         | false  | 1     |       | todo  |
+| ceil          | false  | 1     | true  |       |
+| fetchTree     | true   | 1     |       | todo  |
+| floor         | false  | 1     | true  |       |
+| groupBy       | false  | 2     | true  |       |
+| traceVerbose  | false  | 2     |       | todo  |
+| zipAttrsWith  | false  | 2     | true  | todo  |