minimal functional programming in bash with associative array, prevent pyramid of doom

higherorder.bash

#!/bin/bash
# higher order functions for bash

array(){
  declare -A "$@"
}

# foreach
# example:
#   array foo
#   foo[0]="one" foo[1]="two" foo["bar"]="BAR"
#   bar(){ echo "$1 -> $2"; }
#   foreach foo bar
#   foreach foo keys | grep [0-1] | map pick foo
foreach(){ 
  eval "for i in \"\${!$1[@]}\"; do $2 \"\$i\" \"\$( echo \"\${$1[\$i]}\" )\"; done"
}

keys(){
  echo "$1"
}

values(){
  echo "$2"  
}

pick(){                                                                         
  [[ ! -n $2 ]] && return 1 || eval "echo \${$1[$2]}"
}

# maps a pipe stream to individual calls
# example:
#  foreach foo values | map echo
map(){
  set +m ; shopt -s lastpipe
  cat - | while read line; do "$@" "$line"; done
}

# compose function out of 2 functions
# example: 
#   compose functionname func2 func1
#   functionname "this is input"
compose() {
  result_fun=$1; shift ; f1=$1; shift ; f2=$1; shift
  eval "$result_fun() { $f1 \"\$($f2 \"\$*\")\"; }"
}