Common Lisp Cheat Sheet

A cheat sheet in English by boechat107

[WIP] Hopefully, this cheatsheet lists the most common functions and macros, linking them to the "Common Lisp Hyper Spec".

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Numbers

`parse-integer`	Parses an integer from a string
`floor`, `ceiling`	Truncates toward negative/positive infinity
`round`	Rounds to the nearest integer
`mod`, `rem`	Modulus/remainder of a truncating division
`1+`, `1-`	Returns a new value (inc/dec)remented by a number
`incf`, `decf`	Macros to (inc/dec)rement in place
`=`, `/=`	Mathematical value equality (types ignored)
`>`, `>=`, `<`, `<=`	Order comparison

Characters

Strings

format

Returns a formatted output string when the destination is nil

Sequences

`elt`	Access elements with an integer index
`length`
`count`	Count the appearances of an element
`find`	Finds an item or returns `nil`
`position`	The first index of an element
`search`	Returns the start position of a sequence in another sequence
`remove`	Removes all the occurrences of an item
`substitute`	Replaces all occurrences of an item

Lists

`mapcar`	Successively applies a function to each element of a list
`maplist`	Like `mapcar`, but its function receives a cons cell instead of its element (therefore, the function has access to the rest of the list)
`mapcan`	Like `mapcar`, but the results are combined into a list
`mapcon`	Like `mapcan`, but applied to `maplist`

Vectors

Hash Tables

Things to remember

Object Oriented	All values in a Common Lisp program are instances of some class. Furthermore, all classes are organized into a single hierarchy rooted at the class `T`.
Starting a project	SBCL and Quicklisp installation and a project template

Equality

`eq`	Object identity (don't use with numbers or chars)
`eql`	Considers equivalent two objects of the same class with the same numeric or char value
`equal`	Lists with the same structure and contents, strings with the same characters
`equalp`	Ignores differences in case or in numerical type (`1 == 1.0`)

Functions

`defun`
`lambda`	Returns an anonymous function
`return-from`	Immediately returns a value from a function (or a `block`)
`funcall`	Invokes a function from a function object
`apply`	Works like `funcall`, but receives the arguments as a list
`&optional`, `&key`, `&rest`, `&allow-other-keys`	Different ways to capture function arguments

Standard Control Constructs

`if`	The else form is optional
`when`	Like `if`, but returns `nil` if the condition is falsy and evaluates multiple body forms
`unless`	Like `when`, but executes its body only when the condition is falsy

IO

`format`	Produces formatted output to stdout when the destination is `t`
`format` language
`_a`, `s`,	Interpolate argument in human readable format; interpolate as Lisp readable
`_%`, `&`	Newline; newline if not at the beginning of a line

Object-Oriented

`defgeneric`	Defines an abstract operation (polymorphism)
`defmethod`	Defines an implementation of a generic function
`call-next-method`	Similar to an invocation to a super-class method
`defclass`	New named class; some slot options are: `:reader`, `:writer`, `:accessor`, `:initarg`, `:initform`, `:documentation`, `:allocation`
`slot-value`	Returns the value of slot in the object (`setf`-able)
`with-slots`, `with-accessors`	Binds a slot/accessor to a symbol that can be used in its body

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