Data commit

Task/Universal-Turing-machine/UNIX-Shell/universal-turing-machine.sh

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+main() {
+  printf 'Simple Incrementer\n'
+  printf '1 1 1' | run_utm q0 qf B q0,1,1,R,q0 q0,B,1,S,qf
+
+  printf '\nThree-state busy beaver\n'
+  run_utm a halt 0 \
+    a,0,1,R,b a,1,1,L,c b,0,1,L,a b,1,1,R,b c,0,1,L,b c,1,1,S,halt \
+    </dev/null
+}
+
+run_utm() {
+  local initial=$1 final=$2 blank=$3
+  shift 3
+  local rules=("$@") tape
+  mapfile -t -d' ' tape
+  if (( ! ${#tape[@]} )); then
+    tape=( "$blank" )
+  fi
+  local state=$initial
+  local head=0
+  while [[ $state != $final ]]; do
+    print_state "$state" "$head" "${tape[@]}"
+    local symbol=${tape[head]}
+    local found=0 rule from input output move to
+    for rule in "${rules[@]}"; do
+      IFS=, read from input output move to <<<"$rule"
+      if [[ $state == $from && $symbol == $input ]]; then
+        found=1
+        break
+      fi
+    done
+    if (( ! found )); then
+        printf >&2 "Configuration error: no match for state=$state input=$sym\n"
+        return 1
+    fi
+    tape[head]=$output
+    state=$to
+    case "$move" in
+     L) if (( ! head-- )); then
+          head=0
+          tape=("$blank" "${tape[@]}")
+        fi
+        ;;
+     R) if (( ++head >= ${#tape[@]} )); then
+          tape+=("$blank")
+        fi
+        ;;
+    esac
+  done
+  print_state "$state" "$head" "${tape[@]}"
+}
+
+print_state() {
+  local state=$1 head=$2
+  shift 2
+  local tape=("$@")
+  printf '%s' "$state"
+  printf '  %s' "${tape[@]}"
+  printf '\r'
+  (( t = ${#state} + 1 + 3 * head ))
+  printf '\e['"$t"'C<\e[C>\n'
+}
+
+main "$@"