This package is now both in Emacs 25.1 and ELPA. Further development will only happen there.

Do not send pull requests or open issues here (use M-x report-emacs-bug instead).

seq.el provides Sequence manipulation functions that complement basic functions provided by subr.el. The library is included in Emacs 25.

All functions are prefixed with seq-.

All provided functions work on lists, strings and vectors.

Functions taking a predicate or iterating over a sequence using a function as argument take the function as their first argument and the sequence as their second argument. All other functions take the sequence as their first argument.

All functions are tested in test/seq-tests.el

Note: The version 2 of seq.el is maintained in the Emacs git repository, please consider sending patches there.

seq.el provides the following functions:

• seq-drop seq n

  This function returns a sequence of all but the first n elements of the sequence seq.

  seq may be a list, vector or string and n must be an integer. The result is the same type of sequence as seq.

  If n is a negative integer or zero, seq is returned.

• seq-take seq n

  This function returns a sequence of the first n elements of seq.

  seq may be a list, vector or string and n must be an integer. The result is the same type of sequence as seq.

  If n is a negative integer or zero, an empty sequence is returned.

• seq-take-while pred seq

  This function returns a sub-sequence of the successive elements of seq for which calling pred with that element returns non-nil.

  pred must be a one-argument function and seq may be a list, vector or string. The result is the same type of sequence as seq.

  If evaluating pred with the first element of seq as argument returns nil, an empty sequence is returned.

• seq-drop-while pred seq

  This function returns a sub-sequence of seq from the first element for which calling pred with that element returns nil.

  pred must be a one-argument function and seq may be a list, vector or string. The result is the same type of sequence as seq.

  If evaluating pred with every element of seq returns nil, seq is returned.

• seq-filter pred seq

  This function returns a list of all the elements in seq for which calling pred with that element returns non-nil.

  pred must be a one-argument function and seq may be a list, vector or string.

• seq-map function seq

  This function returns the result of applying function to each element of seq. The returned value is a list.

  function must be a one-argument function and seq may be a list, vector or string.

• seq-mapn function &rest seqs

  This function returns the result of applying function to each element of all seqs. The returned value is a list.

  The arity of FUNCTION must match the number of SEQS, and the mapping stops on the shortest sequence.

• seq-remove pred seq This function returns a list of all the elements in seq for which calling pred with that element returns nil.

  pred must be a one-argument function and seq may be a list, vector or string.

• seq-reduce function seq initial-value This function returns the result of calling function with initial-value and the first element of seq, then calling function with that result and the second element of seq, then with that result and the third element of seq, etc.

  function must be a two-arguments function and seq may be a list, vector or string.

  If seq is empty, initial-value is returned and function is not called.

• seq-some pred seq This function returns non-nil if calling pred with any element of seq returns non-nil. If so, the returned value is the value returned by seq.

  pred must be a one-argument function and seq may be a list, vector or string.

• seq-find pred seq &optional default This function returns the first element for which pred returns non-nil in seq. If no element matches pref, default is returned.

  Note that this function has an ambiguity if the found element is identical to default, as it cannot be known if an element was found or not.

• seq-every-p pred seq This function returns non-nil if successively calling pred with each element of seq always returns non-nil, nil otherwise.

  pred must be a one-argument function and seq may be a list, vector or string.

• seq-empty-p seq This function returns non-nil if the sequence seq is empty, nil otherwise.

  seq may be a list, vector or string.

• seq-count pred seq This function returns the number of elements in seq for which calling pred with that element returns non-nil.

  pred must be a one-argument function and seq may be a list, vector or string.

• seq-sort pred seq This function returns a sorted sequence of the elements of seq, comparing its elements with pred. Called with two elements of seq, pred should return non-nil if the first element should sort before the second.

  pred must be a two-arguments function, seq may be a list, vector or string.

  The result is a sequence of the same type as SEQ.

• seq-contains seq elt testfn This function returns the first element in seq that equals to elt.

  Equality is defined by testfn if non-nil or by equal if nil.

  seq may be a list, vector or string.

• seq-position seq elt testfn This function returns the index of the first element in seq that is equal to elt. Equality is defined by testfn if non-nil or by equal if nil."

  seq may be a list, vector or string.

• seq-uniq seq testfn This function returns a list of the elements of seq with duplicates removed. testfn is used to compare elements, or equal if testfn is nil.

  testfn must be a two-argument function or nil and seq may be a list, vector or string.

• seq-subseq seq start &optional end This function returns a sub-sequence of seq from start to end. If end is omitted, it default to the length of seq. If start or end is negative, it counts from the end of seq.

  seq may be a list, vector or string. The result is the same type of sequence as seq.

• seq-concatenate type &rest seqs This function returns a sequence made of the concatenation of seqs. The result is a sequence of type type. type may be one of the following symbols: vector, list or string.

• seq-mapcat function sequence &optional type This function returns the result of applying seq-concatenate to the result of applying function to each element of sequence. The result is a sequence of type type, or a list if type is nil.

• seq-partition sequence n This function returns a list of the elements of sequence grouped into sub-sequences of length n. The last sequence may contain less elements than n. n must be an integer. If n is a negative integer or 0, nil is returned.

• seq-group-by function sequence This function separates the elements of sequence into an alist whose keys are the result of applying function to each element of sequence. Keys are compared using equal.

• seq-intersection seq1 seq2 &optional testfn Return a list of the elements that appear in both seq1 and seq2. Equality is defined by TESTFN if non-nil or by equal if nil.

• seq-difference seq1 seq2 &optional testfn Return a list of the elements that appear in both seq1 but not in seq2. Equality is defined by TESTFN if non-nil or by equal if nil.

• seq-doseq (var seq [result]) body... This macro is like dolist, except that seq can be a list, vector or string.

  seq-doseq is primarily useful for side-effects.

• seq-let args &rest body Bind the variables in ARGS to the elements of SEQ then evaluate BODY. ARGS can also include the `&rest' marker followed by a variable name to be bound to the rest of SEQ.

Since this library is in Emacs 25, contributors must have signed the Emacs Copyright assignment.

Fetch dependencies:

$ cd /path/to/seq.el
$ cask

Run the tests:

$ ./run-tests.sh