The Slime 1.0 Manual

abstract

\tableofcontents

1 Lisp languages

Lisp is not one language but rather a family of programming languages. The family is devided by some characteristics. There are Lisp-1 and Lisp-2 dialects and there is a difference between a Lisp with lexical scoping as opposed to dynamic scoping. These differences will be explained in later sections.

Like most Lisps, Slime is dynamically typed. That means that like in statically typed Languages Slime has different data types, but they are associated not with variables but with the Lisp objects themselves. Variables can be assigend Lisp objects of any internal type.

The Lisp language family is known to be highly flexible and applicable in all areas by creating domain specific languages in Lisp itself through a powerful macro system. The central data structure in Lisp is the list. The reason why lisp is so powerful is because the program source code itself is represented as lists. The nested lists make up the syntax tree of the lisp program. It is therfore computationally easy to parse lisp programs as the source code itself is already structured in the form of the syntax tree; allowing for parsing in linear time.

The macro system in Slime works by recognizing macros at parse-time and running them, and replacing the macro call in the program code with the return value of the macro and then checking if further macros have to be expanded in the replaced code. Therefore the macros can be used to pre-compute values or rewrite expressions (creating syntactic sugar) or themselves define macros.

2 Lists

As mentioned in Lisp languages, the central data structure in all Lisps is the list. Lists are implemented as singly linked lists, made up of pairs (historically called cons-cells), each pair has two slots, the first and the rest (historically car and cdr). A linked lsit ist then constructed by the convention that the first field of a pair points to the first element of the list and the rest field points to the rest of the list. Following this description, the list is a recursive data structure. For the end of the list a special value nil is used in the rest field.

A helpful way to visualize lists made up of pairs is using box diagrams. A simple box diagram can be seen in 1. Each rectangle is divided in two. The left part represents the first field, the right part represents the rest. The arrows point to the values in these fields.

The diagram in 1 shows a simple list containing the values 1, 2 and 3. The first pair stores the number 1 its first field and the rest points to the rest of the list. The last pair points to the special value nil in its rest to denote the end of the list.

diagrams/list123.eps

However the rest of a pair needs not to be a pair or nil, it could also point to any other value. By doing this the list is no longer "well formed" but rather "ill formed". Ill formed lsits can be used as an optimization when using the list for storing data. In 2 an ill formed list can be seen, that also contains the values 1, 2 and 3 but stores them using only two pairs instead of 3.

diagrams/list12.3.eps

2.1 representing lists in Lisp

In Slime and in most Lisps, lists are represented using round parenthesis where ( denotes the start of the list and ) denotes the end. Eeach element inside these parenthesis separated by one or more spaces will be interpreted as an element of that list. For example the list from 1 would be represented as (1 2 3). During parse time, the Lisp parser transforms the parenthesised list into the pairs that are in the end stored in memory.

To also be able to represent ill formed lists in Lisp there is a special syntax using the . (dot symbol). If the parser encounters a . inside of a list, it will treat the next element as the rest. If there is no or more than one element after the . an parsing error will be thrown. Using this syntax we can represent the ill formed list from 2 as (1 2 . 3). We can also write well formed lists using the dot notation if we point the rest to another list. So the well formed list from 1 can also be written as \[\texttt{(1 . (2 . (3)))}\]

2.2 representing function calls in Lisp

If we tried to enter the Lisp representation of the lists like (1 2 3) discussed in representing lists in Lisp directly into an Lisp interpreter we would get an error. That doesn't mean that the explanation given in the section is wrong, it is in fact correct: the lisp parser will transform the lisp syntax into the pairs in memory. The reason we would get an error is, that when reading Lisp code, the Lisp interpreter first parses the code and then tries to evaluate it and return the result back to the user.

In Lisp by default, a list corresponds to a function call. As mentioned in Lisp languages Lisp represents lists and Lisp programms as lists. If a list is treated as a function call, the first element will be treated as the function and the rest of the elements will be the arguments to that function. If we would wnter (1 2 3) directly into the Lisp interpreter we would get an error saying it cannot find the function 1.

If we would want to compute the sum of the numbers 5 and 3 we could do this by invoking the + function with 5 and 3 as its arguments. (+ 5 3) will evaluate to 8. We can also nest functions calls and use the return values as parameters to other functions: (+ (- 12 4) (/ 24 4)) will evaluate to 14. The box diagramm showing the internal structure of that computation can be seen in 3.

diagrams/simpleMath.eps

3 Evaluation order

As a first step of evaluation of a regular function, all its arguments are getting evaluated, and then the function is applied to the evaluated arguments. For example when evaluating the nested expression in 1 the outermost function is the + function with three arguments: (* 3 4), (- 100 (+ 12 13 14 15)) and 2. So before the outhermost + gets invoked, the three arguments are getting evaluated recursively.

A more complex nested arithmetic expression. Nested expressions can be written more readable by aligning subsequent arguments vertically underneeth each other

(print (+ (* 3 4)
          (- 100 (+ 12 13 14 15))
          2))

evaluates to =>
60

3.1 Special forms

The given evaluation rule – to evaluate all the arguments first and then allpying them to the funciton – as described in Evaluation order is only valid for regular functions. There is a class of functions that do not follow this evaluation rule called special forms. Special forms are needed when you do not wish to evaluate all arguments. For example the built-in if function should only evaluate the "then-expression" if the condition evaluates to a truthy value and not otherwise. Consider the example in 2. The if expression only evaluates the then-expression. If the if function would follow the evaluation order of regular functions, first all three arguments (< 1 2), (print "I knew it!!\n") but also (print "Oh, it is not?!\n") could get evaluated and so both messages would be printed. In the given if expression, the condition evaluates to a truthy value and only I knew it!! will be printed.

The if function is a special form because it does not evaluate all of its arguments

(if (< 1 2)
    (print "I knew it!!\n")
  (print "Oh, it is not?!\n"))

evaluates to =>
I knew it!!

The programmer can also define their own special forms using special-lambda and macros, which will be explained in Special lambdas and Macros.

4 Symbols and keywords

5 Truthyness

6 Lambdas

Slime allows for creating anonymous functions called lambdas. We did not talk about binding variables, we will do this in Define, but we can still use lambdas now. Remember that Lisp interpretes the first argument of a list in the source code as a function and the rest as the arguments. The lambda special form evaluates to a regular function object that can then stand in the first position of the function call list. The basic syntax for the lambda special form is: \[\texttt{(lambda (arg1 arg2 ...) (body1) ...)}\] the first arguemnt to lambda is a list of the arguments. All the following arguments will be the body of the lambda. They will be executed when the lambda is invoked. The return value of a lambda is the value of the last evaluated expression in the body.

Probably the simplest function to write as a lambda is the identity function. It takes one argument and returns it. The identity lambda and a few other simple examples of lambdas can be seen in 3.

Some simle lambdas

(printf ((lambda (x) x) 1))
(printf ((lambda (x y) (+ x y)) 3 5))
(printf ((lambda (x y z) (list x y z)) 1 2 3))

evaluates to =>
1
8
(1 2 3)

Additionally Slime lambdas have the possibility to take optional arguments in the form of keyword arguemnts as well as a rest argument which allows for accepting any number of arguments. Since these concepts are most useful when the function is actually bound to a variable, they will be introduced when we learned how to do that in Define.

6.1 Special lambdas

The lambda special form creates a function object that represents a regular function. So the basic evaluation rules count: when the lambda is invoked all it's arguments are evaluated and then the lambda is applied to the evaluated arguments. If this is not wanted in some rare cases, the programmer also has the possibility to define a special form using special-lambda, which, when invoked does not evaluare any argument. The programmer has to evaluate the arguments in the body themselves using eval. The rest of the syntax between lambda and special-lambda are the same.

Special lambdas do not evaluate their arguments

((lambda         (x) (printf x)) (+ 1 2))
((special-lambda (x) (printf x)) (+ 1 2))

;; Special lambdas make it possible to write
;; code that inspects code
((special-lambda (expr)
     (printf "The function to be called is"
             (first expr)
             "and the result is"
             (eval expr)))
 (+ 1 2))

evaluates to =>
3
(+ 1 2)
The function to be called is + and the result is 3

7 Define

To assign a value to a symbol you can use the define built-in special form. The syntax for define is: \[\texttt{(define symbol value)}\] and some usages can be seen in 5.

Simple definition of variables

(define var1 1)
(define var2 "Hello World")
(define var3 (+ 1 2))

(printf var1 var2 var3)

evaluates to =>
1 Hello World 3

7.1 Defining functions

In Lambdas we learned how to create function objects using the lambda built-in form. Using define every Lisp Object can be assigned to a symbol making no exception for the function objects. In 6 you can see what that would look like.

Definition of functions using lambdas

(define hypothenuse
  (lambda (a b)
    (** (+ (* a a) (* b b)) 0.5)))

(printf (hypothenuse 3 4))

evaluates to =>
5

Since defining functions is so common, there is a syntactic shorthand that does not require to write out the whole lambda definition. In this case the first argument to the call to define is a list. The frist element of the list is the name of the function to define and the other elemens are the arguments to that function. An example can be seen in 7. Note that the definition looks like a call to the function we are constructing, making it easier to see what a call to that function will look like.

Definition of functions using the shorthand syntax of define

(define (hypothenuse a b)
  (** (+ (* a a) (* b b)) 0.5))

(printf (hypothenuse 3 4))

evaluates to =>
5

7.2 Functions with keyword arguments

A sometimes more convenient way of passing arguments to a function is using keyword arguments. Using keyword arguments a function call could look like this: \[\texttt{(function :arg1 value1 :arg2 value2)}\] here the function accepts two arguments named arg1 and arg2. The user of this function can see more clearly excatly which argument will be assigned wich value. This notation also allows for switching the argument order. The following function call is equivalent to the call above. \[\texttt{(function :arg2 value2 :arg1 value1)}\].

For this to work however, the function must be defined to accept these keyword arguments. To do this the special marker :keys has to be inserted into the argument list of a lambda or a function define. All following arguments must be supplied as keyword arguments, unless they are also supplied with a default value, in which case they do not need to be supplied. To attach a default value to a keyword argument, insert :defaults-to <value> after the keyword argument name. An example of all of this can be seen in 8. Important note: keyword arguments must be defined and supplied after all the regular arguments.

A more complex functoin definition using keyword arguments

(define (complex required1 required2 :keys
                 key1
                 key2 :defaults-to 3
                 key3)
  (* (+ required1 required2)
     key1
     key2
     key3))

(printf (complex 1 2 :key1 2 :key2 2 :key3 3))
(printf (complex 1 2 :key1 2 :key3 3))
(printf (complex 1 2 :key3 3 :key1 2))

evaluates to =>
36
54
54

7.3 Functions with rest arguments

If the programmer wants to create a function that can accept any number of arguments, they can use the rest argument. It is defined after the special marker :rest and after the rest argument, no other arguments can be defined. In the execution of the fuction, the rest arguent will be assigned to a list containing all the supplied values. The rest argument can be used in conjunction with the other argument types, regular arguments and keyword arguments.

A more complex functoin definition using keyword arguments

(define (execute-operation operation
                           :keys
                           do-logging :defaults-to ()
                           :rest values)
  (define result (apply operation values))
  (when do-logging
    (printf "Executing operation"
            operation
            "agains the values"
            values
            "yielded:"
            result))
  result)

(printf (execute-operation '+ 1 2 3))
(printf (execute-operation '*
                           :do-logging t
                           10 11))

evaluates to =>
6
Executing operation * agains the values (10 11) yielded: 110
110

8 Environments

9 Macros

Built-in functions

\hrule

`=`

defined in: src/./built_ins.cpp:158:0
type: :cfunction
docu: Takes 0 or more arguments and returns t if all arguments are equal and () otherwise.

\hrule

`>`

defined in: src/./built_ins.cpp:175:0
type: :cfunction
docu: TODO

\hrule

`>=`

defined in: src/./built_ins.cpp:193:0
type: :cfunction
docu: TODO

\hrule

`<`

defined in: src/./built_ins.cpp:211:0
type: :cfunction
docu: TODO

\hrule

`<=`

defined in: src/./built_ins.cpp:231:0
type: :cfunction
docu: TODO

\hrule

`+`

defined in: src/./built_ins.cpp:249:0
type: :cfunction
docu: TODO

\hrule

`-`

defined in: src/./built_ins.cpp:262:0
type: :cfunction
docu: TODO

\hrule

`*`

defined in: src/./built_ins.cpp:285:0
type: :cfunction
docu: TODO

\hrule

`/`

defined in: src/./built_ins.cpp:306:0
type: :cfunction
docu: TODO

\hrule

`**`

defined in: src/./built_ins.cpp:327:0
type: :cfunction
docu: TODO

\hrule

`%`

defined in: src/./built_ins.cpp:343:0
type: :cfunction
docu: TODO

\hrule

`assert`

defined in: src/./built_ins.cpp:359:0
type: :cfunction
docu: TODO

\hrule

`define`

defined in: src/./built_ins.cpp:371:0
type: :cfunction
docu: TODO

\hrule

`mutate`

defined in: src/./built_ins.cpp:433:0
type: :cfunction
docu: TODO

\hrule

`if`

defined in: src/./built_ins.cpp:458:0
type: :cfunction
docu: TODO

\hrule

`quote`

defined in: src/./built_ins.cpp:480:0
type: :cfunction
docu: TODO

\hrule

`quasiquote`

defined in: src/./built_ins.cpp:485:0
type: :cfunction
docu: TODO

\hrule

`and`

defined in: src/./built_ins.cpp:583:0
type: :cfunction
docu: TODO

\hrule

`or`

defined in: src/./built_ins.cpp:594:0
type: :cfunction
docu: TODO

\hrule

`not`

defined in: src/./built_ins.cpp:605:0
type: :cfunction
docu: TODO

\hrule

`while`

defined in: src/./built_ins.cpp:615:0
type: :cfunction
docu: TODO

\hrule

`lambda`

defined in: src/./built_ins.cpp:693:0
type: :cfunction
docu: TODO

\hrule

`special-lambda`

defined in: src/./built_ins.cpp:705:0
type: :cfunction
docu: TODO

\hrule

`eval`

defined in: src/./built_ins.cpp:713:0
type: :cfunction
docu: TODO

\hrule

`begin`

defined in: src/./built_ins.cpp:725:0
type: :cfunction
docu: TODO

\hrule

`list`

defined in: src/./built_ins.cpp:741:0
type: :cfunction
docu: TODO

\hrule

`pair`

defined in: src/./built_ins.cpp:745:0
type: :cfunction
docu: TODO

\hrule

`first`

defined in: src/./built_ins.cpp:755:0
type: :cfunction
docu: TODO

\hrule

`rest`

defined in: src/./built_ins.cpp:766:0
type: :cfunction
docu: TODO

\hrule

`set-type`

defined in: src/./built_ins.cpp:777:0
type: :cfunction
docu: TODO

\hrule

`delete-type`

defined in: src/./built_ins.cpp:789:0
type: :cfunction
docu: TODO

\hrule

`type`

defined in: src/./built_ins.cpp:796:0
type: :cfunction
docu: TODO

\hrule

`info`

defined in: src/./built_ins.cpp:828:0
type: :cfunction
docu: TODO

\hrule

`show`

defined in: src/./built_ins.cpp:910:0
type: :cfunction
docu: TODO

\hrule

`addr-of`

defined in: src/./built_ins.cpp:922:0
type: :cfunction
docu: TODO

\hrule

`generate-docs`

defined in: src/./built_ins.cpp:928:0
type: :cfunction
docu: TODO

\hrule

`print`

defined in: src/./built_ins.cpp:937:0
type: :cfunction
docu: TODO

\hrule

`read`

defined in: src/./built_ins.cpp:945:0
type: :cfunction
docu: TODO

\hrule

`exit`

defined in: src/./built_ins.cpp:962:0
type: :cfunction
docu: TODO

\hrule

`break`

defined in: src/./built_ins.cpp:973:0
type: :cfunction
docu: TODO

\hrule

`memstat`

defined in: src/./built_ins.cpp:978:0
type: :cfunction
docu: TODO

\hrule

`try`

defined in: src/./built_ins.cpp:982:0
type: :cfunction
docu: TODO

\hrule

`load`

defined in: src/./built_ins.cpp:997:0
type: :cfunction
docu: TODO

\hrule

`import`

defined in: src/./built_ins.cpp:1008:0
type: :cfunction
docu: TODO

\hrule

`copy`

defined in: src/./built_ins.cpp:1019:0
type: :cfunction
docu: TODO

\hrule

`error`

defined in: src/./built_ins.cpp:1027:0
type: :cfunction
docu: TODO

\hrule

`symbol->keyword`

defined in: src/./built_ins.cpp:1034:0
type: :cfunction
docu: TODO

\hrule

`string->symbol`

defined in: src/./built_ins.cpp:1043:0
type: :cfunction
docu: TODO

\hrule

`symbol->string`

defined in: src/./built_ins.cpp:1055:0
type: :cfunction
docu: TODO

\hrule

`concat-strings`

defined in: src/./built_ins.cpp:1064:0
type: :cfunction
docu: TODO

\hrule

`pe`

defined in

pre.slime:2:40

type

:macro

arguments

postitional: expr

docu

none

\hrule

`when`

defined in

pre.slime:8:37

type

:macro

arguments

postitional: condition:
rest: body

docu

Doc String for `when'

\hrule

`unless`

defined in

pre.slime:13:41

type

:macro

arguments

postitional: condition:
rest: body

docu

none

\hrule

`n-times`

defined in

pre.slime:20:35

type

:macro

arguments

postitional: times, action

docu

Executes action times times.

\hrule

`let`

defined in

pre.slime:37:64

type

:macro

arguments

postitional: bindings:
rest: body

docu

none

\hrule

`cond`

defined in

pre.slime:51:19

type

:macro

arguments

rest: clauses

docu

none

\hrule

`define-special`

defined in

pre.slime:54:81

type

:macro

arguments

postitional: name-and-args:
rest: body

docu

none

\hrule

`construct-list`

defined in

pre.slime:94:14

type

:macro

arguments

rest: body

docu

(construct-list i <- '(1 2 3 4 5) yield (* i i))

(construct-list i <- '(1 2 3 4) j <- '(A B) yield (pair i j))

(construct-list i <- '(1 2 3 4 5 6 7 8) when (evenp i) yield i)

\hrule

`apply`

defined in

pre.slime:99:28

type

:macro

arguments

postitional: fun, seq

docu

Applies the funciton to the sequence, as in calls the function with ithe sequence as arguemens.

\hrule

`define-package`

defined in

pre.slime:113:24

type

:macro

arguments

postitional: name:
rest: body

docu

none

\hrule

`nil?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is nil.

\hrule

`number?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is a number.

\hrule

`symbol?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is a symbol.

\hrule

`keyword?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is a keyword.

\hrule

`pair?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is a pair.

\hrule

`string?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is a string.

\hrule

`lambda?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is a function.

\hrule

`macro?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is a macro.

\hrule

`special-lambda?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is a special-lambda.

\hrule

`built-in-function?`

type

:lambda

arguments

postitional: x

docu

Checks if the argument is a built-in function.

\hrule

`callable?`

type

:lambda

arguments

postitional: x

docu

none

\hrule

`end`

type

:lambda

arguments

postitional: seq

docu

Returns the last pair in the sqeuence.

\hrule

`last`

type

:lambda

arguments

postitional: seq

docu

Returns the (first) of the last (pair) of the given sequence.

\hrule

`extend`

type

:lambda

arguments

postitional: seq, elem

docu

Extends a list with the given element, by putting it in the (rest) of the last element of the sequence.

\hrule

`extend2`

type

:lambda

arguments

postitional: seq, elem

docu

Extends a list with the given element, by putting it in the (rest) of the last element of the sequence.

\hrule

`append`

type

:lambda

arguments

postitional: seq, elem

docu

Appends an element to a sequence, by extendeing the list with (pair elem nil).

\hrule

`length`

type

:lambda

arguments

postitional: seq

docu

Returns the length of the given sequence.

\hrule

`increment`

type

:lambda

arguments

postitional: val

docu

Adds one to the argument.

\hrule

`decrement`

type

:lambda

arguments

postitional: val

docu

Subtracts one from the argument.

\hrule

`range`

type

:lambda

arguments

keyword: from (0), to

docu

Returns a sequence of numbers starting with the number defined by the key from and ends with the number defined in to.

\hrule

`range-while`

type

:lambda

arguments

keyword: from (0), to

docu

Returns a sequence of numbers starting with the number defined by the key 'from' and ends with the number defined in 'to'.

\hrule

`map`

type

:lambda

arguments

postitional: fun, seq

docu

Takes a function and a sequence as arguments and returns a new sequence which contains the results of using the first sequences elemens as argument to that function.

\hrule

`reduce`

type

:lambda

arguments

postitional: fun, seq

docu

Takes a function and a sequence as arguments and applies the function to the argument sequence. This only works correctly if the given function accepts a variable amount of parameters. If your funciton is limited to two arguments, use reduce-binary instead.

\hrule

`reduce-binary`

type

:lambda

arguments

postitional: fun, seq

docu

Takes a function and a sequence as arguments and applies the function to the argument sequence. reduce-binary applies the arguments `pair-wise' which means it works with binary functions as compared to `reduce'.

\hrule

`filter`

type

:lambda

arguments

postitional: fun, seq

docu

Takes a function and a sequence as arguments and applies the function to every value in the sequence. If the result of that funciton application returns a truthy value, the original value is added to a list, which in the end is returned.

\hrule

`zip`

type

:lambda

arguments

postitional: l1, l2

docu

none

\hrule

`unzip`

type

:lambda

arguments

postitional: lists

docu

none

\hrule

`enumerate`

type

:lambda

arguments

postitional: seq

docu

none

\hrule

`printf`

type

:lambda

arguments

keyword: sep (" "), end ("\n"):
rest: args

docu

A wrapper for the built-in print that accepts a variable number of arguments and also provides keywords for specifying the printed separators (sep) between the arguments and what should be printed after the las argument (end).

\hrule

`define-class`

defined in

oo.slime:22:22

type

:macro

arguments

postitional: name-and-members:
rest: body

docu

Macro for creating simple classes.

\hrule

`->`

defined in

oo.slime:25:24

type

:macro

arguments

postitional: obj, meth:
rest: args

docu

none

\hrule

`math->`

type

:package

arguments

rest: args

docu

none

\hrule

`math-> pi`

defined in: math.slime:5:4
type: :number
value: 3.141593
docu: Tha famous circle constant.

\hrule

`math-> abs`

defined in

math.slime:9:4

type

:lambda

arguments

postitional: x

docu

Accepts one argument and returns the absoulte value of it

\hrule

`math-> sqrt`

defined in

math.slime:13:4

type

:lambda

arguments

postitional: x

docu

Accepts one argument and returns the square root of it

\hrule

`math-> make-vector3`

defined in

pre.slime:37:63

type

:constructor

arguments

postitional: x, y, z

docu

This is the handle to an object of the class vector3

\hrule

`math-> make-vector3 define-class`

defined in

oo.slime:22:22

type

:macro

arguments

postitional: name-and-members:
rest: body

docu

Macro for creating simple classes.

\hrule

`math-> make-vector3 ->`

defined in

oo.slime:25:24

type

:macro

arguments

postitional: obj, meth:
rest: args

docu

none