A Dylan Primer for Scheme Programmers#

This document was originally authored by Jonathan Sobel.

Almost everything you already do in Scheme has a direct counterpart in Dylan.

Note

If one column contains N/A, then that language has no corresponding direct way to express what is in the other column.

Literals#

Scheme

Dylan

 
#t

#t

#f

#f

23

23

#b1011

#b1011

#o644

#o644

#x2A5F

#x2A5F

-4/5

N/A

 
6.02E23

6.02E23

#\a

'a'

#\newline

'\n'

"Hello"

"Hello"

"Hello\n"

"Hello\n"

'apple

#"apple"
apple:

'|two words|

#"two words"

'(1 #\a dog)

#(1, 'a', #"dog")

#(5 10 15)

#[5, 10, 15]

`(1 2 ,x ,@y)

N/A

Syntax#

Note that, in Dylan, any words after an end (e.g. end method) are optional.

Scheme

Dylan

 
(define var exp)

define variable var = exp
define constant var = exp

(f x y z)

f(x, y, z)

(begin 1 2 3)

begin 1; 2; 3; end
begin 1; 2; 3 end

(quote datum)

N/A

 
(lambda (x y . z)
  (say "hello")
  (f x y z))

method (x, y, #rest z)
  say("hello");
  f(x, y, z);
end method

(begin
  (define x 5)
  body)

begin
  let x = 5;
  body
end

(define-values (x y) exp)

let (x, y) = exp;

(let-values (((x y)
              (values 5 6)))
  (f x y))

let (x, y) = values(5, 6);
f(x, y)

(letrec ((f (lambda (x)
        f-body)
   )
   (g (lambda (y z)
        g-body)
   ))
  body)

local method f (x)
  f-body
end method f,
method g (y, z)
  g-body
end method g;
body

(if test
    (begin then1
     then2)
    (begin else1
     else2)
)

if (test)
  then1;
  then2;
else
  else1;
  else2;
end if

(set! var value)

var := value

(and a b c)

a & b & c

(or a b c)

a | b | c

(cond
 (test1 result1)
 (test2 result2)
 (else result)
)

case
  test1 => result1;
  test2 => result2;
  otherwise => result;
end case

(case exp
 ((a 2) result1)
 (('a' 'b') result2)
 (else result)
)

select (exp)
  #"a", 2 => result1;
  'a', 'b' => result2;
  otherwise => result;
end select

N/A

 
select (exp by comparison-func)
  f(x) => result1;
  g(y), h(z) => result2;
  otherwise => result;
end select

(do ((var1 init1 step1)
     (var2 init2 step2))
    (test result)
  body
)

for (var1 = init1 then step1,
     var2 = init2 then step2,
     until: test)
  body
finally result
end for

Predefined functions#

These are organized based on the “Standard Procedures” section of R4RS.

Boolean functions

 
(not obj)

~ obj
~obj

(boolean? obj)

instance?(obj, <boolean>)

Equivalence predicates

 
(eqv? x y)

x == y

(eq? x y)

N/A

 
(equal? x y)

x = y

Pairs and Lists

 
(pair? obj)

instance?(obj, <pair>)

(cons x y)

pair(x, y)

(car ls)

head(ls)

(cdr ls)

tail(ls)

(set-car! ls val)

head-setter(val, ls)
head(ls) := val

(set-cdr! ls val)

tail-setter(val, ls)
tail(ls) := val

(cadadr ls)

N/A

(null? obj)

instance?(obj, <empty-list>)
obj = #()
empty?(ls) // most common

(list? obj)

instance?(obj, <list>)

(list x y z)

list(x, y, z)

(length ls)

size(ls)

(append ls1 ls2 ls3)

concatenate(ls1, ls2, ls3)

(reverse ls)

reverse(ls)

(list-ref ls n)

element(ls, n)

(member obj ls)

member?(obj, ls)

(memv obj ls)

member?(obj, ls, test: \==)

Symbols

 
(symbol? obj)

instance?(obj, <symbol>)

(symbol->string sym)

as(<string>, sym)

(string->symbol str)

as(<symbol>, str)

Numerical operations

 
(number? obj)

instance?(obj, <number>)

(complex? obj)

instance?(obj, <complex>)

(real? obj)

instance?(obj, <real>)

(rational? obj)

instance?(obj, <rational>)

(integer? obj)

instance?(obj, <integer>)
integral?(num)

(= n1 n2)

n1 = n2
n1 == n2

(< n1 n2)

n1 < n2

(> n1 n2)

n1 > n2

(<= n1 n2)

n1 <= n2

(>= n1 n2)

n1 >= n2

(zero? n)

zero?(n)

(positive? n)

positive?(n)

(negative? n)

negative?(n)

(odd? i)

odd?(i)

(even? i)

even?(i)

(+ 1 2 3)

1 + 2 + 3

(* 1 2 3)

1 * 2 * 3

(- 5 3)

5 - 3

(/ 2.3 1.7)

2.3 / 1.7

(- x)

- x
-x

(expt 2 16)

2 ^ 16

[Most of the standard Scheme numeric functions (e.g. max, remainder) are defined similarly in Dylan. No need to list them all here.]

Characters

 
(char? obj)

instance?(obj, <character>)

(char=? char1 char2)

char1 = char2
char1 == char2

(char<? char1 char2)

char1 < char2

(char>? char1 char2)

char1 > char2

(char<=? char1 char2)

char1 <= char2

(char>=? char1 char2)

char1 >= char2

(char->integer char)

as(<integer>, char)

(integer->char n)

as(<character>, n)

(char-upcase char)

as-uppercase(char)

(char-downcase char)

as-lowercase(char)

Strings

 
(string? obj)

instance?(obj, <string>)

(make-string k char)

make(<string>, size: k, fill: char)

(string char ...)

N/A

 
(string-length str)

size(str)

(string-ref str k)

element(str, k)
str[k]

(string-set! str k char)

element-setter(char, str, k)
str[k] := char

(string=? str1 str2)

str1 = str2

(string<? str1 str2)

str1 < str2

(substring str start end)

copy-sequence(str, start: start, end: end)

(string-append str1 str2)

concatenate(str1, str2)

(string->list str)

as(<list>, str)

(list->string chars)

as(<string>, chars)

(string-copy str)

shallow-copy(str)
copy-sequence(str)

(string-fill! str char)

fill!(str, char)

Vectors

 
(vector? obj)

instance?(obj, <vector>)

(make-vector k fill)

make(<vector>, size: k, fill: fill)

(vector obj ...)

vector(obj, ...);

(vector-length vec)

size(vec)

(vector-ref vec k)

element(vec, k)
vec[k]

(vector-set! vec k obj)

element-setter(obj, vec, k)
vec[k] := obj

(vector->list vec)

as(<list>, vec)

(list->vector list)

as(<vector>, list)

(vector-fill! vec obj)

fill!(vec, obj)

Control Features

 
(procedure? obj)

instance?(obj, <function>)

(apply proc arg1 arg2 args)

apply(proc, arg1, arg2, args)

(map proc list1 list2 ...)

map(proc, list1, list2, ...)

(vector-map proc
            vec1 vec2 ...)

map(proc, vec1, vec2, ...)

(string-map
   string1 string2 ...)

map(proc, string1, string2)

(for-each proc list1 list2)

do(proc, list1, list2)

Continuations

Continuations have indefinite extent in Scheme but have dynamic extent in Dylan. Also, whereas call/cc is a function, Dylan uses special syntax to grab a continuation.

 
(call/cc
  (lambda (k)
    body))

block (k)
  body
end block

(call/cc
  (lambda (k)
    (dynamic-wind
      (lambda () #f)
      (lambda () body)
      (lambda ()
         cleanup-stuff))))

block (k)
  body
cleanup
  cleanup-stuff
end block