Vector Library (R7RS-compatible)


John Cowan (based on SRFI 43 by Taylor Campbell)


None at this time.

Table of Contents

1. Status

This SRFI is currently in final status. Here is an explanation of each status that a SRFI can hold. To provide input on this SRFI, please send email to srfi-133@nospamsrfi.schemers.org. To subscribe to the list, follow these instructions. You can access previous messages via the mailing list archive.

Post-finalization note: The finalized version of this SRFI required the equality operator used by the vector= procedure to be consistent with eq?. However, = is not consistent with eq? in a Scheme which provides NaN values and IEEE semantics for them, as (eq? +nan.0 +nan.0) may return either #t or #f but (= +nan.0 +nan.0) must return #f. This means that the expected semantics of = when used with vector= are violated. Therefore, the requirement for consistency has been removed from this version, and the sample implementation adjusted accordingly.

2. Abstract

This SRFI proposes a comprehensive library of vector operations accompanied by a freely available and complete reference implementation. The reference implementation is unencumbered by copyright, and useable with no modifications on any Scheme system that is R5RS-compliant. It also provides several hooks for implementation-specific optimization as well.

3. Rationale

R5RS provides very few list-processing procedures, for which reason SRFI 1 exists. However, R5RS provides even fewer vector operations — while it provides mapping, appending, et cetera operations for lists, it specifies only nine vector manipulation operations:

R7RS-small added support for start and end arguments to vector->list, list->vector and vector-fill!. It also provided seven additional vector procedures, bringing vectors and lists to approximate parity:

SRFI 43 standardized more vector procedures, all of which are included in this SRFI. Unfortunately, R7RS-small and SRFI 43 placed irreconcileable requirements on the procedures invoked by vector-map and vector-for-each. This SRFI resolves that issue by changing these SRFI 43 procedures as well as vector-map!, vector-fold, vector-fold-right, and vector-count to leave out the index argument that is passed under SRFI 43's definition.

In addition, the version of vector-copy in this SRFI does not require support for a fill argument, which makes it equivalent to the R7RS-small definition.

This SRFI also provides the following new procedures (some from Python, some from other sources):

It should be noted that no vector sorting procedures are provided by this SRFI, because there already are several SRFIs for that purpose.

4. Procedure Index

Here is an index of the procedures provided by this package. Those marked by italics are also provided in R7RS-small.

· Constructors

make-vector vector
vector-unfold vector-unfold-right
vector-copy vector-reverse-copy
vector-append vector-concatenate vector-append-subvectors

· Predicates


· Selectors


· Iteration

vector-fold vector-fold-right
vector-map vector-map!
vector-for-each vector-count

· Searching

vector-index vector-index-right
vector-skip vector-skip-right
vector-any vector-every

· Mutators

vector-set! vector-swap!
vector-fill! vector-reverse!
vector-copy! vector-reverse-copy!
vector-unfold! vector-unfold-right!

· Conversion

vector->list reverse-vector->list
list->vector reverse-list->vector
vector->string string->vector

5. Procedures

In this section containing specifications of procedures, the following notation is used to specify parameters and return values:

(f arg1 arg2 ...) -> something
Indicates a function f takes the parameters arg1 arg2 ... and returns a value of the type something. If something is unspecified, then f returns a single implementation-dependent value; this SRFI does not specify what it returns, and in order to write portable code, the return value should be ignored.

The argument in this place must be a vector, i.e. it must satisfy the predicate vector?.

i, j, start, size
The argument in this place must be a exact nonnegative integer, i.e. it must satisfy the predicates exact?, integer? and either zero? or positive?. The third case of it indicates the index at which traversal begins; the fourth case of it indicates the size of a vector.

The argument in this place must be a exact positive integer, i.e. it must satisfy the predicates exact?, integer? and positive?. This indicates the index directly before which traversal will stop — processing will occur until the the index of the vector is end. It is the closed right side of a range.

The argument in this place must be a function of one or more arguments, which returns (except as noted otherwise) exactly one value.

The argument in this place must be a function of one or more arguments that returns one value, which is treated as a boolean.

x, y, z, seed, knil, fill, key, value
The argument in this place may be any Scheme value.

Indicates that something is an optional argument; it needn't necessarily be applied. Something needn't necessarily be one thing; for example, this usage of it is perfectly valid:

   [start [end]]

and is indeed used quite often.

something ...
Indicates that zero or more somethings are allowed to be arguments.

something1 something2 ...
Indicates that at least one something must be arguments.

something1 something2 ... somethingn
Exactly equivalent to the previous argument notation, but this also indicates that n will be used later in the procedure description.

It should be noted that all of the procedures that iterate across multiple vectors in parallel stop iterating and produce the final result when the end of the shortest vector is reached. The sole exception is vector=, which automatically returns #f if the vectors' lengths vary.

5.1. Constructors

(make-vector size [fill]) -> vector
[R7RS-small] Creates and returns a vector of size size. If fill is specified, all the elements of the vector are initialized to fill. Otherwise, their contents are indeterminate.


(make-vector 5 3)
#(3 3 3 3 3)

(vector x ...) -> vector
[R7RS-small] Creates and returns a vector whose elements are x ....


(vector 0 1 2 3 4)
#(0 1 2 3 4)

(vector-unfold f length initial-seed ...) -> vector
The fundamental vector constructor. Creates a vector whose length is length and iterates across each index k between 0 and length, applying f at each iteration to the current index and current seeds, in that order, to receive n + 1 values: first, the element to put in the kth slot of the new vector and n new seeds for the next iteration. It is an error for the number of seeds to vary between iterations. Note that the termination condition is different from the unfold procedure of SRFI 1.


(vector-unfold (λ (i x) (values x (- x 1)))
                 10 0)

#(0 -1 -2 -3 -4 -5 -6 -7 -8 -9)

Construct a vector of the sequence of integers in the range [0,n).
(vector-unfold values n)
#(0 1 2 ... n-2 n-1)

Copy vector.

(vector-unfold (λ (i) (vector-ref vector i))
                 (vector-length vector))

(vector-unfold-right f length initial-seed ...) -> vector
Like vector-unfold, but it uses f to generate elements from right-to-left, rather than left-to-right. The first index used is length - 1. Note that the termination condition is different from the unfold-right procedure of SRFI 1.


Construct a vector of pairs of non-negative integers whose values sum to 4.

(vector-unfold-right (λ (i x) (values (cons i x) (+ x 1))) 5 0)
#((0 . 4) (1 . 3) (2 . 2) (3 . 1) (4 . 0))

Reverse vector.

(vector-unfold-right (λ (i x) (values (vector-ref vector x) (+ x 1)))
                       (vector-length vector)

(vector-copy vec [start [end]]) -> vector
[R7RS-small] Allocates a new vector whose length is end - start and fills it with elements from vec, taking elements from vec starting at index start and stopping at index end. Start defaults to 0 and end defaults to the value of (vector-length vec). SRFI 43 provides an optional fill argument to supply values if end is greater than the length of vec. Neither R7RS-small nor this SRFI requires support for this argument.


(vector-copy '#(a b c d e f g h i))
#(a b c d e f g h i)

(vector-copy '#(a b c d e f g h i) 6)
#(g h i)

(vector-copy '#(a b c d e f g h i) 3 6)
#(d e f)

(vector-reverse-copy vec [start [end]]) -> vector
Like vector-copy, but it copies the elements in the reverse order from vec.


(vector-reverse-copy '#(5 4 3 2 1 0) 1 5)
#(1 2 3 4)

(vector-append vec ...) -> vector
[R7RS-small] Returns a newly allocated vector that contains all elements in order from the subsequent locations in vec ....


(vector-append '#(x) '#(y))
#(x y)

(vector-append '#(a) '#(b c d))
#(a b c d)

(vector-append '#(a #(b)) '#(#(c)))
#(a #(b) #(c))

(vector-concatenate list-of-vectors) -> vector
Appends each vector in list-of-vectors. This is equivalent to:

(apply vector-append list-of-vectors)

However, it may be implemented better.


(vector-concatenate '(#(a b) #(c d)))
#(a b c d)

(vector-append-subvectors [vec start end] ...) -> vector
Returns a vector that contains every element of each vec from start to end in the specified order. This procedure is a generalization of vector-append.


(vector-append-subvectors '#(a b c d e) 0 2 '#(f g h i j) 2 4)
#(a b h i)

5.2. Predicates

(vector? x) -> boolean
[R7RS-small] Disjoint type predicate for vectors: this returns #t if x is a vector, and #f if otherwise.


(vector? '#(a b c))

(vector? '(a b c))

(vector? #t)

(vector? '#())

(vector? '())

(vector-empty? vec) -> boolean
Returns #t if vec is empty, i.e. its length is 0, and #f if not.


(vector-empty? '#(a))

(vector-empty? '#(()))

(vector-empty? '#(#()))

(vector-empty? '#())

(vector= elt=? vec ...) -> boolean
Vector structure comparator, generalized across user-specified element comparators. Vectors a and b are considered equal by vector= iff their lengths are the same, and for each respective element Ea and Eb, (elt=? Ea Eb) returns a true value. Elt=? is always applied to two arguments.

If there are only zero or one vector arguments, #t is automatically returned. The dynamic order in which comparisons of elements and of vectors are performed is left completely unspecified; do not rely on a particular order.


(vector= eq? '#(a b c d) '#(a b c d))

(vector= eq? '#(a b c d) '#(a b d c))

(vector= = '#(1 2 3 4 5) '#(1 2 3 4))

(vector= = '#(1 2 3 4) '#(1 2 3 4))

The two trivial cases.

(vector= eq?)

(vector= eq? '#(a))

Note the fact that we don't use vector literals in the next two — it is unspecified whether or not literal vectors with the same external representation are eq?.

(vector= eq? (vector (vector 'a)) (vector (vector 'a)))

(vector= equal? (vector (vector 'a)) (vector (vector 'a)))

5.3. Selectors

(vector-ref vec i) -> value
[R7RS-small] Vector element dereferencing: returns the value that the location in vec at i is mapped to in the store. Indexing is based on zero. I must be within the range [0, (vector-length vec)).


(vector-ref '#(a b c d) 2)

(vector-length vec) -> exact nonnegative integer
[R7RS-small] Returns the length of vec, the number of locations reachable from vec. (The careful word 'reachable' is used to allow for 'vector slices,' whereby vec refers to a larger vector that contains more locations that are unreachable from vec. This SRFI does not define vector slices, but later SRFIs may.)


(vector-length '#(a b c))

5.4. Iteration

(vector-fold kons knil vec1 vec2 ...) -> value
The fundamental vector iterator. Kons is iterated over each value in all of the vectors, stopping at the end of the shortest; kons is applied as (kons state (vector-ref vec1 i) (vector-ref vec2 i) ...) where state is the current state value — the current state value begins with knil, and becomes whatever kons returned on the previous iteration —, and i is the current index.

The iteration is strictly left-to-right.


Find the longest string's length in vector-of-strings.
(vector-fold (λ (len str) (max (string-length str) len))
               0 vector-of-strings)

Produce a list of the reversed elements of vec.
(vector-fold (λ (tail elt) (cons elt tail))
               '() vec)

Count the number of even numbers in vec.
(vector-fold (λ (counter n)
                 (if (even? n) (+ counter 1) counter))
               0 vec)

(vector-fold-right kons knil vec1 vec2 ...) -> value
Similar to vector-fold, but it iterates right to left instead of left to right.


Convert a vector to a list.
(vector-fold-right (λ (tail elt) (cons elt tail))
                     '() '#(a b c d))

(a b c d)

(vector-map f vec1 vec2 ...) -> vector
[R7RS-small] Constructs a new vector of the shortest size of the vector arguments. Each element at index i of the new vector is mapped from the old vectors by (f (vector-ref vec1 i) (vector-ref vec2 i) ...). The dynamic order of application of f is unspecified.


(vector-map (λ (x) (* x x))
              (vector-unfold (λ (i x) (values x (+ x 1))) 4 1))

#(1 4 9 16)

(vector-map (λ (x y) (* x y))
              (vector-unfold (λ (x) (values x (+ x 1))) 5 1)
              (vector-unfold (λ (x) (values x (- x 1))) 5 5))

#(5 8 9 8 5)

(let ((count 0))
   (vector-map (λ (ignored-elt)
                 (set! count (+ count 1))
               '#(a b)))
#(1 2) OR #(2 1)

(vector-map! f vec1 vec2 ...) -> unspecified
Similar to vector-map, but rather than mapping the new elements into a new vector, the new mapped elements are destructively inserted into vec1. Again, the dynamic order of application of f unspecified, so it is dangerous for f to apply either vector-ref or vector-set! to vec1 in f.
(vector-for-each f vec1 vec2 ...) -> unspecified
[R7RS-small] Simple vector iterator: applies f to the corresponding list of parallel elements from vec1 vec2 ... in the range [0, length), where length is the length of the smallest vector argument passed, In contrast with vector-map, f is reliably applied to each subsequent element, starting at index 0, in the vectors.


(vector-for-each (λ (x) (display x) (newline))
                 '#("foo" "bar" "baz" "quux" "zot"))
(vector-count pred? vec1 vec2 ...) -> exact nonnegative integer
Counts the number of parallel elements in the vectors that satisfy pred?, which is applied, for each index i in the range [0, length) where length is the length of the smallest vector argument, to each parallel element in the vectors, in order.


(vector-count even? '#(3 1 4 1 5 9 2 5 6))

(vector-count < '#(1 3 6 9) '#(2 4 6 8 10 12))

(vector-cumulate f knil vec) -> vector
Returns a newly allocated vector new with the same length as vec. Each element i of new is set to the result of invoking f on newi-1 and veci, except that for the first call on f, the first argument is knil. The new vector is returned.

Note that the order of arguments to vector-cumulate was changed by errata-3 on 2016-09-02.


(vector-cumulate + 0 '#(3 1 4 1 5 9 2 5 6))
#(3 4 8 9 14 23 25 30 36)

5.5. Searching

(vector-index pred? vec1 vec2 ...) -> exact nonnegative integer or #f
Finds & returns the index of the first elements in vec1 vec2 ... that satisfy pred?. If no matching element is found by the end of the shortest vector, #f is returned.


(vector-index even? '#(3 1 4 1 5 9))

(vector-index < '#(3 1 4 1 5 9 2 5 6) '#(2 7 1 8 2))

(vector-index = '#(3 1 4 1 5 9 2 5 6) '#(2 7 1 8 2))

(vector-index-right pred? vec1 vec2 ...) -> exact nonnegative integer or #f
Like vector-index, but it searches right-to-left, rather than left-to-right, and all of the vectors must have the same length.

(vector-skip pred? vec1 vec2 ...) -> exact nonnegative integer or #f
Finds & returns the index of the first elements in vec1 vec2 ... that do not satisfy pred?. If all the values in the vectors satisfy pred? until the end of the shortest vector, this returns #f. This is equivalent to:

(vector-index (λ (x1 x2 ...) (not (pred? x1 x1 ...)))
                    vec1 vec2 ...)


(vector-skip number? '#(1 2 a b 3 4 c d))

(vector-skip-right pred? vec1 vec2 ...) -> exact nonnegative integer or #f
Like vector-skip, but it searches for a non-matching element right-to-left, rather than left-to-right, and it is an error if all of the vectors do not have the same length. This is equivalent to:

(vector-index-right (λ (x1 x2 ...) (not (pred? x1 x1 ...)))
                          vec1 vec2 ...)

(vector-binary-search vec value cmp) -> exact nonnegative integer or #f

Similar to vector-index and vector-index-right, but instead of searching left to right or right to left, this performs a binary search. If there is more than one element of vec that matches value in the sense of cmp, vector-binary-search may return the index of any of them.

cmp should be a procedure of two arguments and return a negative integer, which indicates that its first argument is less than its second, zero, which indicates that they are equal, or a positive integer, which indicates that the first argument is greater than the second argument. An example cmp might be:

(λ (char1 char2)
  (cond ((char<? char1 char2) -1)
        ((char=? char1 char2) 0)
        (else 1)))

(vector-any pred? vec1 vec2 ...) -> value or #f
Finds the first set of elements in parallel from vec1 vec2 ... for which pred? returns a true value. If such a parallel set of elements exists, vector-any returns the value that pred? returned for that set of elements. The iteration is strictly left-to-right.

(vector-every pred? vec1 vec2 ...) -> value or #f
If, for every index i between 0 and the length of the shortest vector argument, the set of elements (vector-ref vec1 i) (vector-ref vec2 i) ... satisfies pred?, vector-every returns the value that pred? returned for the last set of elements, at the last index of the shortest vector. The iteration is strictly left-to-right.

(vector-partition pred? vec) -> vector and integer
A vector the same size as vec is newly allocated and filled with all the elements of vec that satisfy pred? in their original order followed by all the elements that do not satisfy pred?, also in their original order.

Two values are returned, the newly allocated vector and the index of the leftmost element that does not satisfy pred?.

5.7. Mutators

(vector-set! vec i value) -> unspecified
[R7RS-small] Assigns the contents of the location at i in vec to value.

(vector-swap! vec i j) -> unspecified
Swaps or exchanges the values of the locations in vec at i & j.

(vector-fill! vec fill [start [end]]) -> unspecified
[R7RS-small] Assigns the value of every location in vec between start, which defaults to 0 and end, which defaults to the length of vec, to fill.

(vector-reverse! vec [start [end]]) -> unspecified
Destructively reverses the contents of the sequence of locations in vec between start and end. Start defaults to 0 and end defaults to the length of vec. Note that this does not deeply reverse.

(vector-copy! to at from [start [end]]) -> unspecified
[R7RS-small] Copies the elements of vector from between start and end to vector to, starting at at. The order in which elements are copied is unspecified, except that if the source and destination overlap, copying takes place as if the source is first copied into a temporary vector and then into the destination. This can be achieved without allocating storage by making sure to copy in the correct direction in such circumstances.

(vector-reverse-copy! to at from [start [end]]) -> unspecified
Like vector-copy!, but the elements appear in to in reverse order.

(vector-unfold! f vec start end initial-seed ...) -> unspecified
Like vector-unfold, but the elements are copied into the vector vec starting at element start rather than into a newly allocated vector. Terminates when end-start elements have been generated.

(vector-unfold-right! f vec start end initial-seed ...) -> unspecified
Like vector-unfold!, but the elements are copied in reverse order into the vector vec starting at the index preceding end.

5.8. Conversion

(vector->list vec [start [end]]) -> proper-list
[R7RS-small] Creates a list containing the elements in vec between start, which defaults to 0, and end, which defaults to the length of vec.

(reverse-vector->list vec [start [end]]) -> proper-list
Like vector->list, but the resulting list contains the elements in reverse of vec.

(list->vector proper-list) -> vector
[R7RS-small] Creates a vector of elements from proper-list.

(reverse-list->vector proper-list) -> vector
Like list->vector, but the resulting vector contains the elements in reverse of proper-list.

(string->vector string [start [end]]) -> vector
[R7RS-small] Creates a vector containing the elements in string between start, which defaults to 0, and end, which defaults to the length of string.

(vector->string vec [start [end]]) -> string
[R7RS-small] Creates a string containing the elements in vec between start, which defaults to 0, and end, which defaults to the length of vec. It is an error if the elements are not characters.

6. Sample Implementation

The sample implementation is in the repository of this SRFI. It has only one non-R5RS dependency: SRFI 23's error procedure, which is also provided by R7RS-small. It is in the public domain, or alternatively under the same copyright as this SRFI. The following files are provided:

7. Acknowledgements

These acknowledgements are copied from SRFI 43.

Thanks to Olin Shivers for his wonderfully complete list and string packages; to all the members of the #scheme IRC channel on Freenode who nitpicked a great deal, but also helped quite a lot in general, and helped test the reference implementation in various Scheme systems; to Michael Burschik for his numerous comments; to Sergei Egorov for helping to narrow down the procedures; to Mike Sperber for putting up with an extremely overdue draft; to Felix Winkelmann for continually bugging me about finishing up the SRFI so that it would be only overdue and not withdrawn; and to everyone else who gave questions, comments, thoughts, or merely attention to the SRFI.

8. References

R5RS: The Revised5 Report on Scheme
R. Kelsey, W. Clinger, J. Rees (editors).
Higher-Order and Symbolic Computation, Vol. 11, No. 1, September, 1998
ACM SIGPLAN Notices, Vol. 33, No. 9, October, 1998
Available at: http://www.schemers.org/Documents/Standards/R5RS/

R7RS: The Revised7 Report on Scheme
A. Shinn et al. (editors).
Available at: http://r7rs.org

SRFI: Scheme Request for Implementation
The SRFI website can be found at: https://srfi.schemers.org/
The SRFIs mentioned in this document are described later.

SRFI 1: List Library
A SRFI of list processing procedures, written by Olin Shivers.
Available at: https://srfi.schemers.org/srfi-1/

SRFI 13: String Library
A SRFI of string processing procedures, written by Olin Shivers.
Available at: https://srfi.schemers.org/srfi-13/

SRFI 23: Error Reporting Mechanism
A SRFI that defines a new primitive (error) for reporting that an error occurred, written by Stephan Houben.
Available at: https://srfi.schemers.org/srfi-23/

SRFI 43: Vector Library (draft)
The direct predecessor of this SRFI, written by Taylor Campbell.
Available at: https://srfi.schemers.org/srfi-43/

9. Copyright

Copyright (C) Taylor Campbell (2003). All rights reserved.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.


Editor: Arthur A. Gleckler