Portable shell script cargo typing and runtime expression parsing experiment

idiom.sh

set -euf
PATH=
IFS=
_r=
_v=0 # variable counter
_f=1 # scopedion namespace
_x=0 # parser namespace

! command -v emulate >/dev/null 2>&1 || emulate ksh >/dev/null 2>&1
command -v local >/dev/null 2>&1 || alias local=typeset

xp () {
    test -n "${1:-}" || return 1
    test "$1" = '[' || set -- [ "$@" ]

    while test $# -gt 0
    do
        if test "$1" = '['
        then _x=$(($_x + 1))
        elif test "$1" = ']'
        then
            test "$_x" -gt 0 || return 1
            eval "eval \"\$_x_$_x\"; _x=$(($_x - 1))"
            eval "_x_$_x=\"$_r\""
            unset "_x_"$((_x + 1))
        else
            case "$1" in
                '@'*) val "${1#"@"}";;
                'n'*) num "${1#"n"}";;
                   *) _r="$1";;
            esac
            eval "_x_$_x=\"\${_x_$_x:-}$_r \""
        fi
        shift
    done

    if test "$_x" = 0
    then unset _x_0
    elif test "$_x" = 1 && test "$_r" = $((_x_$_x))
    then unset _x_1
    else return 1
    fi
}

## FLOW CONTROL

_shift_xp () {
    shift $1;
    xp "$@"
}

var () {
    _r=
    _shift_xp 3 "$@"
    val_usage "$_r" +1
    eval "_f$_f=\"\${_f$_f:- }$1 \""
    eval "$1='$_r'"
}

scoped () {
    _f="$((_f + 1))"
    eval "_f$_f=;_f${_f}l=${_v:-0}"
}

result () {
    _r=${1:-$_r}
    _gc_uvars
    _gc_scope $_r
    _f="$((_f - 1))"
}

## GARBAGE COLLECTION

_gc_val () {
    if eval test \"\${_${1}r:-0}\" = 0
    then val_invoke "$1" destroy
    fi
}

_gc_uvars () {
    IFS=' '
    eval "set -- \$_f$_f"
    IFS=''
    
    while test $# -gt 0
    do eval val_usage "\$$1" -1; shift
    done
    
    unset "_f$_f"
}

_gc_scope () {
    local _vlow _vhigh
    eval "_vlow=\${_f${_f}l:-0}; _vhigh=\$((_v - _vlow))"

    while test $_vhigh -gt $_vlow
    do
        test "$_vhigh" = "$1" || _gc_val "$_vhigh"
        _vhigh=$((_vhigh - 2))
    done

    unset "_f${_f}l"
}

## TYPES

val_invoke () {
    local method="$2" vid="$1"
    shift 2
    eval "eval \"\\\${_\$(($vid - 1)):-seq}_$method $vid \\\"\\\$@\\\"\""
}

val_usage () {
    eval "_${1}r=\$((\${_${1}r:-} + $2))"
}

val_destroy () {
    unset "_${1}" "_${1}r" "_$(($1 - 1))"
}

val () {
    _v=$((_v + 1))
    eval "_$_v='val'"
    _v=$((_v + 1))
    eval "_$_v='$1'"
    _r="$_v"
}

num () {
    _v=$((_v + 1))
    eval "_$_v='num'"
    _v=$((_v + 1))
    eval "_$_v='$1'"
    _r="$_v"
}

num_destroy () {
    val_destroy "$@"
}

seq () {
    _v=$((_v + 2))
    eval "_$_v=''"
    _r="$_v"

    while test $# -gt 0
    do seq_push $_v $1; shift
    done
}

seq_destroy () {
    local _name="$1"
    IFS=' '
    eval "set -- \$_$1"
    IFS=''

    while test $# -gt 0
    do val_usage "$1" -1; shift
    done
    
    val_destroy $_name
}

seq_push () {
    val_usage "$2" +1
    eval "_$1=\"\${_$1:- }$2 \""
}




hello () { 
    scoped
    local greetings greetings2

    var greetings = seq @"Hello " n10 $1
    var greetings2 = seq @"Hello " n15 $1
    
    result $greetings
    return
}

var zoid = hello @"Alexandre"
result $zoid
set
eval : $_r \$_$_r