Update documentation

Author: antonmedv

docs/Language-Definition.md

@@ -53,7 +53,6 @@
     </tr>
 </table>
 
-
 ## Operators
 
 <table>
@@ -126,8 +125,8 @@ foo matches "^[A-Z].*"
 ### Membership Operator
 
 Fields of structs and items of maps can be accessed with `.` operator
-or `[]` operator. Elements of arrays and slices can be accessed with 
-`[]` operator. Negative indices are supported with `-1` being 
+or `[]` operator. Elements of arrays and slices can be accessed with
+`[]` operator. Negative indices are supported with `-1` being
 the last element.
 
 The `in` operator can be used to check if an item is in an array or a map.
@@ -169,7 +168,6 @@ array[3:] == [4, 5]
 array[:] == array
 ```
 
-
 ## Built-in Functions
 
 ### all(array, predicate)
@@ -238,122 +236,262 @@ int("123") == 123
 
 Returns the float value of a number or a string.
 
-### string()
+### string(v)
 
-todo
+Converts the given value `v` into a string representation.
 
-### trim()
+```expr
+string(123) == "123"
+```
 
-todo
+### trim(v[, chars])
 
-### trimPrefix()
+Removes white spaces from both ends of a string `v`.
+If the optional `chars` argument is given, it is a string specifying the set of characters to be removed.
 
-todo
+```expr
+trim("  Hello  ") == "Hello"
+trim("__Hello__", "_") == "Hello"
+```
 
-### trimSuffix()
+### trimPrefix(v, prefix)
 
-todo
+Removes the specified prefix from the string `v` if it starts with that prefix.
 
-### upper()
+```expr
+trimPrefix("HelloWorld", "Hello") == "World"
+```
 
-todo
+### trimSuffix(v, suffix)
 
-### lower()
+Removes the specified suffix from the string `v` if it ends with that suffix.
 
-todo
+```expr
+trimSuffix("HelloWorld", "World") == "Hello"
+```
 
-### split()
+### upper(v)
 
-todo
+Converts all the characters in string `v` to uppercase.
 
-### splitN()
+```expr
+upper("hello") == "HELLO"
+```
 
-todo
+### lower(v)
 
-### splitAfter()
+Converts all the characters in string `v` to lowercase.
 
-todo
+```expr
+lower("HELLO") == "hello"
+```
 
-### splitAfterN()
+### split(v, delimiter)
 
-todo
+Splits the string `v` at each instance of the delimiter and returns an array of substrings.
 
-### replace()
+```expr
+split("apple,orange,grape", ",") == ["apple", "orange", "grape"]
+```
 
-todo
+### splitN(v, delimiter, n)
 
-### repeat()
+Splits the string `v` at each instance of the delimiter but limits the result to `n` substrings.
 
-todo
+```expr
+splitN("apple,orange,grape", ",", 2) == ["apple", "orange,grape"]
+```
 
-### join()
+### splitAfter(v, delimiter)
 
-todo
+Splits the string `v` after each instance of the delimiter.
 
-### indexOf()
+```expr
+splitAfter("apple,orange,grape", ",") == ["apple,", "orange,", "grape"]
+```
 
-todo
+### splitAfterN(v, delimiter, n)
 
-### lastIndexOf()
+Splits the string `v` after each instance of the delimiter but limits the result to `n` substrings.
 
-todo
+```expr
+splitAfterN("apple,orange,grape", ",", 2) == ["apple,", "orange,grape"]
+```
 
-### hasPrefix()
+### replace(v, old, new)
 
-todo
+Replaces all occurrences of `old` in string `v` with `new`.
 
-### hasSuffix()
+```expr
+replace("Hello World", "World", "Universe") == "Hello Universe"
+```
 
-todo
+### repeat(v, n)
 
-### max()
+Repeats the string `v` `n` times.
 
-todo
+```expr
+repeat("Hi", 3) == "HiHiHi"
+```
+
+### join(v, delimiter)
+
+Joins an array of strings `v` into a single string with the given delimiter.
+
+```expr
+join(["apple", "orange", "grape"], ",") == "apple,orange,grape"
+```
 
-### min()
+### indexOf(v, substring)
 
-todo
+Returns the index of the first occurrence of the substring in string `v` or -1 if not found.
 
-### toJSON()
+```expr
+indexOf("apple pie", "pie") == 6
+```
 
-todo
+### lastIndexOf(v, substring)
 
-### fromJSON()
+Returns the index of the last occurrence of the substring in string `v` or -1 if not found.
 
-todo
+```expr
+lastIndexOf("apple pie apple", "apple") == 10
+```
 
-### toBase64()
+### hasPrefix(v, prefix)
 
-todo
+Returns `true` if string `v` starts with the given prefix.
 
-### fromBase64()
+```expr
+hasPrefix("HelloWorld", "Hello") == true
+```
+
+### hasSuffix(v, suffix)
+
+Returns `true` if string `v` ends with the given suffix.
+
+```expr
+hasSuffix("HelloWorld", "World") == true
+```
+
+### max(v1, v2)
+
+Returns the maximum of the two values `v1` and `v2`.
+
+```expr
+max(5, 7) == 7
+```
 
-todo
+### min(v1, v2)
+
+Returns the minimum of the two values `v1` and `v2`.
+
+```expr
+min(5, 7) == 5
+```
+
+### toJSON(v)
+
+Converts the given value `v` to its JSON string representation.
+
+```expr
+toJSON({"name": "John", "age": 30})
+```
+
+### fromJSON(v)
+
+Parses the given JSON string `v` and returns the corresponding value.
+
+```expr
+fromJSON('{"name": "John", "age": 30}')
+```
+
+### toBase64(v)
+
+Encodes the string `v` into Base64 format.
+
+```expr
+toBase64("Hello World") == "SGVsbG8gV29ybGQ="
+```
+
+### fromBase64(v)
+
+Decodes the Base64 encoded string `v` back to its original form.
+
+```expr
+fromBase64("SGVsbG8gV29ybGQ=") == "Hello World"
+```
 
 ### now()
 
-todo
+Returns the current date and time.
+
+```expr
+createdAt > now() - duration(1h)
+```
+
+### duration(v)
+
+Returns [time.Duration](https://pkg.go.dev/time#Duration) value of the given string `v`.
 
-### duration()
+Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
 
-todo
+```expr
+duration("1h").Seconds() == 3600
+```
+
+### date(v[, format, timezone])
 
-### date()
+Converts the given value `v` into a date representation.
 
-todo
+If the optional `format` argument is given, it is a string specifying the format of the date.
+The format string uses the same formatting rules as the standard
+Go [time package](https://pkg.go.dev/time#pkg-constants).
 
-### first()
+If the optional `timezone` argument is given, it is a string specifying the timezone of the date.
 
-todo
+If the `format` argument is not given, the `v` argument must be in one of the following formats:
 
-### last()
+- 2006-01-02
+- 15:04:05
+- 2006-01-02 15:04:05
+- RFC3339
+- RFC822,
+- RFC850,
+- RFC1123,
 
-todo
+```expr
+date("2023-08-14")
+date("15:04:05")
+date("2023-08-14T00:00:00Z")
+date("2023-08-14 00:00:00", "2006-01-02 15:04:05", "Europe/Zurich")
+```
 
-### get()
+### first(v)
 
-todo
+Returns the first element from an array `v`. If the array is empty, returns `nil`.
 
+```expr
+first([1, 2, 3]) == 1
+```
+
+### last(v)
+
+Returns the last element from an array `v`. If the array is empty, returns `nil`.
+
+```expr
+last([1, 2, 3]) == 3
+```
+
+### get(v, index)
+
+Retrieves the element at the specified index from an array or map `v`. If the index is out of range, returns `nil`.
+Or the key does not exist, returns `nil`.
+
+```expr
+get([1, 2, 3], 1) == 2
+get({"name": "John", "age": 30}, "name") == "John"
+```
 
 ## Predicate