Vectors­Cowan

Some cleanup is needed to SRFI 43.

R7RS vs. SRFI 43

The R7RS procedures vector-map and vector-for-each are incompatible with SRFI 43; they do not pass the current index, but only the values. Here's a proposal to fork SRFI 43 to eliminate the problem:

• vector-fold, vector-fold-right, vector-reduce, vector-reduce-right, vector-map, vector-map!, vector-for-each are the R7RS-compatible versions that don't transmit index values to their procedure arguments.
• vector-index-fold, vector-index-fold-right, vector-index-reduce, vector-index-reduce-right, vector-index-map, vector-index-map!, vector-index-for-each do transmit index values, and are compatible with SRFI 43 conceptually but not in name.

Possible extensions

Here are some vector procedures that might be Good Things if we are going to break SRFI 43 anyway. Some are from Python, some from other sources.

Partitioning

(vector-partition pred vector)

Returns two values. The first value is a vector index n, and the second element is a newly allocated vector of the same length as vector, reordered so that the elements which satisfy pred appear in the first n elements of the vector, and the elements which do not satisfy pred appear in the remaining elements. The ordering of the elements is preserved in all other respects . Pred may be called any number of times and in any order.

(vector-partition! pred vector)

The same as vector-partition, except that it mutates vector and returns only n.

Appending

(vector-append-subvectors k fill ( at vector start end ) ...)

Returns a newly allocated vector of length k after copying every element of each vector from start to end into the new vector starting at at. Any additional locations in the new vector are initialized with fill. This procedure is a generalization of vector-copy and vector-copy!. Implementations may optimize this procedure using an unsafe primitive that creates an uninitialized vector, in order to avoid touching each element of the result twice.

Cumulation

(vector-cumulate proc seed vector)

Returns a newly allocated vector of the same length as vector. Each element is constructed by reducing (as if by vector-reduce) successive prefixes of the elements of vector. (APL scan.)

Bisecting

(vector-bisect-left vector comparator obj [ start [ end ] ])

(vector-bisect-right vector comparator obj [ start [ end ] ])

Returns the insertion point for obj in vector to maintain the sorted order of the elements according to comparator. It is an error if vector is not already sorted. If obj is equal to one or more elements of vector, vector-bisect-left will return the insertion point before (to the left of) all matching elements, whereas vector-bisect-right will return the insertion point after (to the right of) all matching elements.

The returned value partitions vector into two halves so that all values with lower indexes are less than or equal to obj and all other values are greater than or equal to obj.