Core Functions: The Pulse of the Language

This page provides a reference for the most fundamental built-in functions in Lispex. These functions are essential for basic data inspection and manipulation.

first

Returns the first element of a list.

• Syntax: (first LIST)
• Arguments:
  • LIST: The list from which to get the first element. Must not be empty.
• Returns: The first element of the list.
• Throws: A RuntimeError if the list is empty.

Example:

(first (list 10 20 30))
;; Result: 10

(first (list "a" "b" "c"))
;; Result: "a"

rest

Returns a new list containing all elements except the first one.

• Syntax: (rest LIST)
• Arguments:
  • LIST: The list to process.
• Returns: A new list containing the rest of the elements. If the original list is empty or has only one element, it returns an empty list.
• Throws: A RuntimeError if the argument is not a list.

Example:

(rest (list 10 20 30))
;; Result: (list 20 30)

(rest (list 10))
;; Result: (list)

(rest (list))
;; Result: (list)

empty?

Checks if a list is empty.

• Syntax: (empty? LIST)
• Arguments:
  • LIST: The list to check.
• Returns: #t if the list has no elements, #f otherwise.
• Throws: A RuntimeError if the argument is not a list.

Example:

(empty? (list))
;; Result: #t

(empty? (list 1 2))
;; Result: #f

length

Returns the number of elements in a list.

• Syntax: (length LIST)
• Arguments:
  • LIST: The list whose length you want to measure.
• Returns: An integer representing the number of elements in the list.
• Throws: A RuntimeError if the argument is not a list.

Example:

(length (list 10 20 30))
;; Result: 3

(length (list))
;; Result: 0

list?

Checks if a given value is a list.

• Syntax: (list? VALUE)
• Arguments:
  • VALUE: The value to check.
• Returns: #t if the value is a list, #f otherwise. This function does not throw an error.

Example:

(list? (list 1 2))
;; Result: #t

(list? 123)
;; Result: #f

(list? "hello")
;; Result: #f