Toy functional tools for the shell

func.sh

#!/bin/sh

lambda() {
    if [ ! $__lambda ]; then
        __lambda=`printf "lambda_%s" $(date +%s)`
        eval "        \
        $__lambda() { \
            $1;       \
        };"
    fi

    $__lambda "$2"
}

__lambda_cleanup() {
    if [ $__lambda ]; then
        unset $__lambda
        unset __lambda
    fi
}

map() {
    for x in $2; do
        eval $1 $x
    done
    __lambda_cleanup
}

filter() {
    for x in $2; do
        if eval $1 $x; then
            echo $x
        fi
    done
    __lambda_cleanup
}

reduce() {
    for x in $2; do
        if [ $__has_one ]; then
            z=`eval $1 $z $x`
        else
            z=$x
            __has_one=1
        fi
    done
    echo $z
    unset __has_one
    __lambda_cleanup
}

succ() {
    bc << EOF
    $1 + 1
EOF
}

pred() {
    bc << EOF
    $1 - 1
EOF
}

division() {
    bc << EOF
    scale=12
    $1 / $2
EOF
}

##########################################################

echo reduce:
reduce division "`seq 1 5`"

echo filter:
filter \
    "lambda '[ \$1 -gt 5 ]'" \
    "`seq 1 10`"

echo map:
map succ "1 2 3 4 5"