diff --git a/docs/spec/system.html b/docs/spec/system.html
index c34b88d7..faf4a07f 100644
--- a/docs/spec/system.html
+++ b/docs/spec/system.html
@@ -53,6 +53,10 @@
+•HashMap |
+
+
| Time |
•UnixTime, •Delay, •_timed, … |
@@ -664,6 +668,48 @@
Keys returns field names as strings, normalized in the sense that all underscores are removed and alphabetic characters are converted to lowercase. The order of the names is unspecified. Has and Get accept names with any spelling. Get causes an error if 𝕩 isn't the name of a field of 𝕨, while Has causes an error only if it isn't a string, returning 0 for any string that isn't a valid name.
+
+The system function •HashMap creates a mutable object from the list of initial keys 𝕨 and values 𝕩 that maintains an association mapping keys to values. It has the following fields:
+
+
+
+| Name |
+Summary |
+
+
+
+
+Count |
+return the number of keys present |
+
+
+Keys |
+return all keys as a list in the order they were set |
+
+
+Values |
+return all values corresponding to the keys |
+
+
+Has |
+return 1 if key 𝕩 is present and 0 otherwise |
+
+
+Get |
+return value for key 𝕩, and 𝕨 or error if not found |
+
+
+Set |
+set value for key 𝕨 to 𝕩, possibly replacing an existing value |
+
+
+Delete |
+remove the entry for key 𝕩 |
+
+
+
+Fields Count, Keys, and Values take one argument and ignore it. Set and Delete return the map object itself.
+Any BQN value can be used as a key, and two keys are considered the same if they match (as in ≡). The initial key list 𝕨 passed to •HashMap can't contain duplicates, that is, the function errors if ¬∧´∊𝕨. This key list defines the initial ordering used by Keys, which may then be modified by Set and Delete. When Set adds a key that's not currently present, that key is added to the end of the ordering. When Delete removes a key, it's removed from the ordering, and will be added to the end if set again.
diff --git a/spec/system.md b/spec/system.md
index 75c77c4e..c3e3f0a6 100644
--- a/spec/system.md
+++ b/spec/system.md
@@ -19,6 +19,7 @@ All system values described in the BQN specification are optional: an implementa
| [Platform](#platform) | `•platform`
| [Operation properties](#operation-properties) | `•Type`, `•Glyph`, `•Source`, `•Decompose`
| [Namespaces](#namespaces) | `•ns`
+| [Data structures](#data-structures) | `•HashMap`
| [Time](#time) | `•UnixTime`, `•Delay`, `•_timed`, …
| [Math](#math) | `•math`
| [Random generation](#random-generation) | `•rand`, `•MakeRand`
@@ -316,6 +317,24 @@ The system namespace `•ns` contains functionality for working with namespaces.
`Keys` returns field names as strings, normalized in the sense that all underscores are removed and alphabetic characters are converted to lowercase. The order of the names is unspecified. `Has` and `Get` accept names with any spelling. `Get` causes an error if `𝕩` isn't the name of a field of `𝕨`, while `Has` causes an error only if it isn't a string, returning `0` for any string that isn't a valid name.
+## Data structures
+
+The system function `•HashMap` creates a mutable object from the list of initial keys `𝕨` and values `𝕩` that maintains an association mapping keys to values. It has the following fields:
+
+| Name | Summary
+|----------|-------------------------------
+| `Count` | return the number of keys present
+| `Keys` | return all keys as a list in the order they were set
+| `Values` | return all values corresponding to the keys
+| `Has` | return `1` if key `𝕩` is present and `0` otherwise
+| `Get` | return value for key `𝕩`, and `𝕨` or error if not found
+| `Set` | set value for key `𝕨` to `𝕩`, possibly replacing an existing value
+| `Delete` | remove the entry for key `𝕩`
+
+Fields `Count`, `Keys`, and `Values` take one argument and ignore it. `Set` and `Delete` return the map object itself.
+
+Any BQN value can be used as a key, and two keys are considered the same if they match (as in `≡`). The initial key list `𝕨` passed to `•HashMap` can't contain duplicates, that is, the function errors if `¬∧´∊𝕨`. This key list defines the initial ordering used by `Keys`, which may then be modified by `Set` and `Delete`. When `Set` adds a key that's not currently present, that key is added to the end of the ordering. When `Delete` removes a key, it's removed from the ordering, and will be added to the end if set again.
+
## Time
| Name | Summary