lolcat is an additional list function which aspect uses almost every day. Once you come to love it, you will too!
It's a portmanteau of lmap, {*} and concat:
proc lolcat args { concat {*}[uplevel 1 lmap $args] }
It's useful in cases where you want to lmap, but the body might need to yield multiple results for a single iteration. Here's a simple example:
% lolcat {x y} {1 2 3 4} {list $y $x} 2 1 4 3 % lolcat x {1 2 3 4} {if {$x%2} {list $x $x} else {list $x}} 1 1 2 3 3 4
To understand how it works, remember that concat concatenates lists, and concat {*}$ls receives the elements of $ls as arguments. Thus, concat {*}$ls will flatten (one level of) a list:
% concat {*}{{1 2} {3 4 5} {6 {7 8}} 9} 1 2 3 4 5 6 {7 8} 9 # equivalently: % concat {1 2} {3 4 5} {6 {7 8}} 9 1 2 3 4 5 6 {7 8} 9
One neat extension on lolcat is dictify:
proc dictify {cmdPrefix ls} { lconcat x $ls { list $x [uplevel 1 $cmdPrefix [list $x]] } }
This allows you to make a dictionary whose keys are a list, and values are the result of evaluating a command on each element.
% dictify {expr 2**} {1 2 3 4 5} 1 2 2 4 3 8 4 16 5 32
Or more elaborately:
% proc pdict {d} {array set {} $d; parray {}} % pdict [dictify {tcl::pkgconfig get} [tcl::pkgconfig list]] debug = 0 threaded = 1 profiled = 0 64bit = 0 optimized = 1 mem_debug = 0 compile_debug = 0 compile_stats = 0 libdir,runtime = /home/tcl/lib bindir,runtime = /home/tcl/bin scriptdir,runtime = /home/tcl/lib/tcl8.6 includedir,runtime = /home/tcl/include docdir,runtime = /home/tcl/man libdir,install = /home/tcl/lib bindir,install = /home/tcl/bin scriptdir,install = /home/tcl/lib/tcl8.6 includedir,install = /home/tcl/include docdir,install = /home/tcl/man
The name comes courtesy hypnotoad - previously I called this procedure lconcat, which is obviously a terrible name. Perhaps it should really be lolmap, but that's not nearly as cute.