docs: details on new added modules (#3971)

web/book/src/SUMMARY.md

@@ -33,8 +33,6 @@
   - [Ranges](./reference/syntax/ranges.md)
   - [Comments](./reference/syntax/comments.md)
   - [Parameters](./reference/syntax/parameters.md)
-  - [Date & time](./reference/syntax/date-time/index.md)
-    - [Format specifiers](./reference/syntax/date-time/format-specifiers.md)
 
 - [Declarations]()
   <!-- I don't know what to call this section. -->
@@ -60,6 +58,9 @@
     - [Window](./reference/stdlib/transforms/window.md)
 
   - [Aggregation functions]()
+  - [Date functions](./reference/stdlib/date.md)
+  - [Mathematical functions](./reference/stdlib/math.md)
+  - [Text functions](./reference/stdlib/string.md)
 
 - [Specification](./reference/spec/README.md)
 

web/book/src/reference/syntax/date-time/format-specifiers.md → web/book/src/reference/stdlib/date.md

@@ -1,4 +1,50 @@
-# Date & time format specifiers
+# Date functions
+
+These are all the functions defined in the `date` module:
+
+### `to_text`
+
+Converts a date into a text.\
+Since there are many possible date representations, `to_text` takes a `format` parameter
+that describes thanks to [specifiers](#date--time-format-specifiers) how the date
+or timestamp should be structured.
+
+```admonish info
+Since all RDBMS have different ways to format dates and times, PRQL **requires an explicit dialect** to be specified
+```
+
+```admonish info
+For now the supported DBs are: Clickhouse, DuckDB, MySQL, MSSQL and Postgres.
+```
+
+```prql
+prql target:sql.duckdb
+
+from invoices
+select {
+  invoice_date | date.to_text "%d/%m/%Y"
+}
+```
+
+```prql
+prql target:sql.postgres
+
+from invoices
+select {
+  invoice_date | date.to_text "%d/%m/%Y"
+}
+```
+
+```prql
+prql target:sql.mysql
+
+from invoices
+select {
+  invoice_date | date.to_text "%d/%m/%Y"
+}
+```
+
+### Date & time format specifiers
 
 PRQL specifiers for date and time formatting is a subset of specifiers used by
 [`chrono`](https://docs.rs/chrono/latest/chrono/format/strftime/index.html).

web/book/src/reference/stdlib/math.md

@@ -0,0 +1,34 @@
+# Mathematical functions
+
+These are all the functions defined in the `math` module:
+
+| function | parameters | description                        |
+| -------- | ---------- | ---------------------------------- |
+| abs      | `col`      | Absolute value of `col`            |
+| acos     | `col`      | Arccosine of `col`                 |
+| asin     | `col`      | Arcsine of `col`                   |
+| atan     | `col`      | Arctangent of `col`                |
+| ceil     | `col`      | Rounds the number up of `col`      |
+| cos      | `col`      | Cosine of `col`                    |
+| degrees  | `col`      | Converts radians to degrees        |
+| exp      | `col`      | Exponential of `col`               |
+| floor    | `col`      | Rounds the number down             |
+| ln       | `col`      | Natural logarithm of `col`         |
+| log      | `b` `col`  | `b`-log of `col`                   |
+| log10    | `col`      | 10-log of `col`                    |
+| pi       |            | The constant π                     |
+| pow      | `b` `col`  | Computes `col` to the power `b`    |
+| radians  | `col`      | Converts degrees to radians        |
+| round    | `n` `col`  | Rounds `col` to `n` decimal places |
+| sin      | `col`      | Sin of `col`                       |
+| sqrt     | `col`      | Square root of `col`               |
+| tan      | `col`      | Tangent of `col`                   |
+
+### Example
+
+```prql
+from employees
+select {
+  age_squared = age | math.pow 2
+}
+```

web/book/src/reference/stdlib/string.md

@@ -0,0 +1,27 @@
+# Text functions
+
+These are all the functions defined in the `string` module:
+
+| function    | parameters             | description                                                                   |
+| ----------- | ---------------------- | ----------------------------------------------------------------------------- |
+| contains    | `text` `col`           | Returns true if `col` contains `text`                                         |
+| ends_with   | `text` `col`           | Returns true if `col` ends with `text`                                        |
+| length      | `col`                  | Returns the number of characters in `col`                                     |
+| lower       | `col`                  | Converts `col` to lower case                                                  |
+| ltrim       | `col`                  | Removes all the whitespaces from the left side of `col`                       |
+| replace     | `before` `after` `col` | Replaces any occurrences of `before` with `after` in `col`                    |
+| rtrim       | `col`                  | Removes all the whitespaces from the right side of `col`                      |
+| starts_with | `text` `col`           | Returns true if `col` starts with `text`                                      |
+| substring   | `idx` `len` `col`      | Extracts a substring at the index `idx` (starting at 1) with the length `len` |
+| trim        | `col`                  | Removes all the whitespaces from both sides of `col`                          |
+| upper       | `col`                  | Converts `col` to upper case                                                  |
+
+### Example
+
+```prql
+from employees
+select {
+  last_name | string.lower | string.starts_with("a"),
+  title | string.replace "manager" "chief"
+}
+```

web/book/tests/documentation/snapshots/documentation__book__reference__stdlib__math__example__0.snap

@@ -0,0 +1,9 @@
+---
+source: web/book/tests/documentation/book.rs
+expression: "from employees\nselect {\n  age_squared = age | math.pow 2\n}\n"
+---
+SELECT
+  POW(age, 2) AS age_squared
+FROM
+  employees
+

web/book/tests/documentation/snapshots/documentation__book__reference__stdlib__string__example__0.snap

@@ -0,0 +1,10 @@
+---
+source: web/book/tests/documentation/book.rs
+expression: "from employees\nselect {\n  last_name | string.lower | string.starts_with(\"a\"),\n  title | string.replace \"manager\" \"chief\"\n}\n"
+---
+SELECT
+  LOWER(last_name) LIKE CONCAT('a', '%'),
+  REPLACE(title, 'manager', 'chief')
+FROM
+  employees
+