lisp.md

Common Lisp driver

ni supports Common Lisp via SBCL, which is available using the l and L operators. For example:

$ ni n4l'(+ a 2)'
3
4
5
6

If you don't have SBCL installed locally, you can use the C (containerize) operator to run a Docker image:

if ! [[ -e /nodocker ]]; then

$ docker build -q -t ni-test/sbcl - <<EOF > /dev/null
FROM ubuntu
RUN apt-get update
RUN apt-get install -y sbcl
CMD /bin/bash
EOF
$ ni Cni-test/sbcl[n4l'(+ a 2)']
3
4
5
6

fi                      # -e /nodocker

Basic stuff

a to q are one-letter functions that return the first 17 tab-delimited values from the current line. (r ...) is a function that takes a list of values and prints a tab-delimited row. For example:

$ ni n4l'(r a (1+ a))'                  # generate two columns
1	2
2	3
3	4
4	5
$ ni n4l'(r a (1+ a))' l'(r (+ a b))'   # ... and sum them
3
5
7
9

Note that whitespace is required after every l'code' operator; otherwise ni will assume that everything following your quoted code is also Lisp.

It is possible to omit r altogether; then you're returning one or more values, each of which will become a row of output:

$ ni n2l'a (+ a 100)'                   # return without "r"
1
101
2
102

Streaming lookahead

This is implemented in terms of reducers, and gives you the ability to reduce arbitrarily many rows in constant space. There are two parts to this. First, the streaming reduce functions se and sr; and second, compound reducers (very useful, and explained in the next section).

sr

Reduces the entire data stream:

sr (reducer value [initial-value])* => reduced-value*

For example, to sum arbitrarily many numbers in constant space:

$ ni n10000l"(sr ('+ a))"
50005000

Or to reduce multiple columns into a row:

$ ni n4fAA l"(r (sr ('+ a) ('* b)))"
10	24

se

Reduces over a contiguous group of rows for which the partition function remains equal. (Mnemonic is "stream while equal".)

se function value-form partition-form [initial-value] => reduced-value

For example, to naively get a comma-delimited list of users by login shell:

$ ni /etc/passwd F::gG l"(r g (se (partial #'join #\,) a g))"
/bin/bash	root
/bin/false	syslog
/bin/sh	backup,bin,daemon,games,gnats,irc,libuuid,list,lp,mail,man,news,nobody,proxy,sys,uucp,www-data
/bin/sync	sync