{{Library}} Here is a library of functions tested in ghostscript. It is assumed to be loaded before startup with a command line such as ghostscript -q -dNODISPLAY -c '(initlib.ps) run'

initlib.ps

```postscript

%!PS
% conventions: parameter names with let begins with .

% basic definition, makes the definitions less verbose.
/. {bind def} bind def
/' {load} bind def
/reverse {{} exch {exch [3 1 roll aload pop]} forall}.
/let {dup length dict begin reverse {exch def} forall}.
/let* {reverse {exch def} forall}.

% some predicates.
/eq? {eq}.
/list? {dup type /arraytype eq?}.
/leaf? {list? not}.
/empty? {dup length 0 eq?}.
/zero? {dup 0 eq?}.
% stack invariant, execute any predicate and leave stack untouched
% except for answer.
/? {
4 dict begin
    [/.pred] let*
    count array astore /.stack exch def
    /_restore {clear .stack aload pop}.
    .stack aload pop .pred /.top exch def
    _restore .top
end}.


% stacky functions
/rup {3 1 roll}.
/rdown {3 -1 roll}.
/# {exch dup rdown .makeoperator bind def} bind def

/getname {dup 0 get exch}.
/getbody {dup length 1 sub 1 exch getinterval}.

% convenience arithmetic
/+ {add}.
/- {sub}.
/* {mul}.
/\ {div}.

% lispy functions
/first {0 get}.
/car {first}.
/!first {dup first}.
/rest {dup length 1 sub 1 exch getinterval}.
/cdr {rest}.
/!rest {dup rest}.
/head  {dup length 1 sub 0 exch getinterval}.
/!head {dup head}.
/tail  {dup length 1 sub get}.
/!tail {dup tail}.
/cons  {[rup aload pop]}.
/tadd  {[rup aload length 1 add -1 roll] }.
/uncons {getname getbody}.
/concat {exch [ rup aload pop counttomark -1 roll aload pop ] }.
% make a unit list.
/unit {1 array astore cvx}.
/succ {1 add}.
/pred {1 sub}.
/range {[rup exch aload pop rup exch rdown {} for]}.

% higher order thingies.
/map { [ rup forall ] }.
% [1 2 3 4] {1 add} map
/fold {rup exch rdown forall}.
%/reverse {{} {exch cons} fold}.
% {} [1 2 3 4 5] {exch cons} forall

% [1 2 3 4] 0 {+} fold
% name - filter is taken so we are left with..
/find {
4 dict begin
    /aif {0 /get /if}.
    /atox { [ exch cvx {cvx} forall ] cvx}.
    [ rup [ /dup rdown /exec /not [{pop}] aif ] atox forall ]
end}.

/transpose {
    [ exch {
        { {empty? exch pop} map all?} {pop exit} ift
        [ exch {} {uncons {exch cons} dip exch} fold counttomark 1 roll] uncons
    } loop ] {reverse} map
}.
/zip {[rup] transpose}.

% [[1 2 3 4 ] [5 6 7 8] [9 10 11 12]]  transpose
/all? {
    {
        {empty?} ? {pop true exit} if
        uncons {?} dip exch not {pop false exit} if
    } loop
}.
% 1 {{10 gt} {5 gt} {0 gt}} any?
/any? {
    {
        {empty?} ? {pop false exit} if
        uncons {?} dip exch {pop true exit} if
    } loop
}.
/pipe {
    {
        {empty?} ? {pop exit} if
        uncons {i} dip
    } loop
}.
%  1 {{2 *} {3 *} {5 *}} pipe
/collect {
    {
        {empty?} ? {pop exit} if
        uncons {?} dip
    } loop
}.
%  1 {{2 *} {3 *} {5 *}} collect

% do on all elements of a tree.
/treemap {
[/.tree /.rec] let
    /.tree '
    {leaf?} /.rec '
        {{empty?} {}
            {dup
                {first /.rec ' treemap} dip
                {rest /.rec ' treemap} i cons}
        ifte}
    ifte
end}.

% control structures
% ift - allow stack invariant if condition
/ift {
[/.if /.then] let
    /.if ' ?  /.then ' if
end}.
% ift - allow stack invariant ifelse condition
/ifte {
[/.if /.then /.else] let
    /.if ' ?  /.then ' /.else ' ifelse
end}.
% switch statement.
/is? {{exit} concat cvx ift}.
/cond {{exit} concat cvx loop}.

% combinators
/dip {
[/.v /.q] let
    .q /.v '
end}.
/apply {exec}.
/i {cvx exec}.

/linrec {
[/.if /.then /.rec1 /.rec2] let
    /.if ' /.then '
        {.rec1
            {/.if ' /.then ' /.rec1 ' /.rec2 ' linrec} i
        .rec2}
    ifte
end}.

/binrec {
[/.if /.then /.rec1 /.rec2] let
    /.if ' /.then '
        { .rec1
            {/.if ' /.then ' /.rec1 ' /.rec2 ' binrec} dip
            {/.if ' /.then ' /.rec1 ' /.rec2 ' binrec} i
          .rec2 }
    ifte
end}.

/genrec {
[/.if /.then /.rec1 /.rec2] let
    /.if ' /.then '
        {.rec1
            {/.if ' /.then ' /.rec1 ' /.rec2 ' genrec}
         .rec2}
    ifte
end}.

/tailrec {{} linrec}.

/primrec {
5 dict begin
    /lzero? {
        {list?} {empty?}
                {zero?}
        ifte}.
    /lnext {
        {list?} {rest}
                {pred}
        ifte}.
[/.param /.then /.rec] let*
    {/.param ' lzero?} /.then '
        {.param
            {/.param ' lnext /.then ' /.rec ' primrec} i
        .rec}
    ifte
end}.

/cvstr {
    4 dict begin
        /elements exch def
        /len elements length def
        /str len string def
        /i 0 def
        {
        i len ge { exit } if
        str i
        %The element of the array, as a hexadecimal string.
        %If it exceeds 16#FF, this will fail with a rangecheck.
        elements i get cvi
        put
        /i i 1 add def
    } loop
    str
end
} def


% debug
/puts {= (\n) print flush}.
/, {(
### =======
\n)
    print pstack
    (
### =======
\n) print}.

% set the prompt to something else so that we know initlib is loaded.
/prompt {(>| ) print flush} bind def