added POSIX AWK port

README.md

@@ -27,6 +27,7 @@ If you want to create your own implementation of LTTB, see the [Implementation N
 Here are all currently known implementations of LTTB:
 
 * [Jim Tcl port](./lttb.tcl) (284 SLOC)
+* [POSIX AWK port](./lttb.awk) (280 SLOC)
 
 ## Test suite
 

lttb-impl-notes.md

@@ -24,7 +24,7 @@ Initial values:
 * `PROGMEM` = empty
 * `VARS["A"]..VARS["Z"] = 0`
 * `CALLSTACK` = empty
-* `IP` = 0
+* `IP = 0`
 
 ## Overall interpreter session flow
 
@@ -90,6 +90,8 @@ Simple two-value evaluator. Accepts two stacks, value stack `VALSTACK` and opera
 
 Mathematical expression and intrinsic function application engine. Accepts a single `EXPR` string as a parameter.
 
+Requires a precedence map `PRECMAP` to be pre-defined as follows: `"(" => 0, "+" => 1, "-" => 1, "*" => 2, "/" => 2, "$" => 3`.
+
 1. Trim leading/trailing whitespace from `EXPR`.
 2. If `EXPR` is empty, return 0.
 3. Initialize `VALSTACK` and `OPSTACK` as empty stacks.
@@ -198,7 +200,7 @@ Value and string printing routine. Accepts `STMT` string as a parameter.
 1. Initialize an empty list `PRINTLIST` and an empty string buffer `ITEM`.
 2. Set the `QUOTING` flag to 0.
 3. Fetch the next character `C` from `STMT`. Go to step 10 if there are no more characters.
-4. If `C` is a double quote `"`, then flip the `QUOTING` flag (set `QUOTING = 1 - QUOTING`), append the value of `C` to `ITEM` and go to step 3. Otherwise, go to step 6.
+4. If `C` is a double quote `"`, then flip the `QUOTING` flag (set `QUOTING = 1 - QUOTING`), append the value of `C` to `ITEM` and go to step 3. Otherwise, go to step 5.
 5. If the `QUOTING` flag is set, append the value of `C` to `ITEM` and go to step 3.
 6. If `C` is either a comma (`,`) or a semicolon (`;`), go to step 7, otherwise go to step 9.
 7. If the current `ITEM` value is not empty, append it to the `PRINTLIST` and clear the `ITEM` variable.

lttb.awk

@@ -0,0 +1,326 @@
+#!/usr/bin/env awk -f
+# Luxferre's Truly Tiny BASIC, POSIX AWK port
+# Adheres to the LTTB Implementation Notes
+# Usage: POSIXLY_CORRECT=1 awk -f lttb.awk [ -- program.bas]
+# Created by Luxferre in 2026, released into the public domain
+
+# Helper functions (AWK-specific)
+
+function wstrim(s) {gsub(/^[[:space:]]+|[[:space:]]+$/, "", s);return s}
+
+function alen(a, i, k) {k = 0;for(i in a) k++;return k}
+
+function ttyinput(s) {
+  if ((getline s < "/dev/stdin") <= 0) exit
+  return wstrim(s)
+}
+
+function stackpush(a, el,   l) {
+  l = alen(a)
+  a[l] = el
+  return l + 1
+}
+
+function stackpop(a,  l, el) {
+  l = alen(a) - 1
+  el = a[l]
+  delete a[l]
+  return el
+}
+
+function precmap(op) {
+  if(op == "(") return 0
+  else if(op == "+" || op == "-") return 1
+  else if(op == "*" || op == "/") return 2
+  else if(op == "$") return 3
+  else return -1
+}
+
+function stacktop(a) {return a[alen(a) - 1]}
+
+# Main LTTB algorithms start here
+
+# numeric value normalizer to 16-bit signed integers
+function norm(val) {
+  if(length(val) == 0) return 0
+  val = int(val)
+  val = (val + 32768) % 65536
+  if(val < 0) val += 65536
+  return val - 32768
+}
+
+# evaluation helper (operates on VALSTACK and OPSTACK)
+function evalhelper(op, v1, v2, res) {
+  res = 0
+  op = stackpop(OPSTACK)
+  v2 = stackpop(VALSTACK)
+  v1 = stackpop(VALSTACK)
+  if(op == "$") res = int(rand() * ((v2 + 32768) % 32768))
+  else if(op == "+") res = v1 + v2
+  else if(op == "-") res = v1 - v2
+  else if(op == "*") res = v1 * v2
+  else if(op == "/" && v2 != 0) res = v1 / v2
+  stackpush(VALSTACK, norm(res))
+}
+
+# main expression evaluator
+function expreval(expr,  valbuf, c, prevc, i, l) {
+  gsub("[[:space:]]+", "", expr)
+  if(length(expr) == 0) return 0
+  split("", OPSTACK)
+  split("", VALSTACK)
+  i = 0
+  l = length(expr)
+  valbuf = prevc = ""
+  for(i=0;i<l;i++) {
+    c = substr(expr, i+1, 1)
+    if(c == int(c)) valbuf = valbuf c
+    else {
+      if(length(valbuf) > 0) {
+        stackpush(VALSTACK, norm(valbuf))
+        valbuf = ""
+      }
+      if(substr(toupper(expr), i+1, 3) == "RND") {
+        stackpush(VALSTACK, 0)
+        c = "$"
+        i += 2        
+      }
+      if(c ~ /[a-zA-Z]/) stackpush(VALSTACK, norm(VARS[toupper(c)]))
+      else if(c == "(") stackpush(OPSTACK, "(")
+      else if(c == ")") {
+        while(stacktop(OPSTACK) != "(" && alen(OPSTACK) > 0) evalhelper()
+        if(alen(OPSTACK) > 0) stackpop(OPSTACK)
+      }
+      if(c == "$" || c == "+" || c == "-" || c == "*" || c == "/") {
+        if((c == "+" || c == "-") && (prevc == "" || prevc == "(" || prevc == "$" || prevc == "+" || prevc == "-" || prevc == "*" || prevc == "/")) stackpush(VALSTACK, 0)
+        while(alen(OPSTACK) > 0 && precmap(stacktop(OPSTACK)) >= precmap(c)) evalhelper()
+        stackpush(OPSTACK, c)
+      }
+    }
+    prevc = c
+  }
+  if(length(valbuf) > 0) stackpush(VALSTACK, norm(valbuf))
+  while(alen(OPSTACK) > 0) evalhelper()
+  return stackpop(VALSTACK)
+}
+
+# internal language routines
+
+function do_GO(stmt) {IP = expreval(stmt) - 1}
+
+function do_GOS(stmt) {stackpush(CALLSTACK, IP); do_GO(stmt)}
+
+function do_RE(stmt) {IP = stackpop(CALLSTACK)}
+
+function do_LE(stmt,  vname, eqp, expr) {
+  vname = toupper(substr(stmt, 1, 1))
+  if(vname ~ /[A-Z]/) {
+    eqp = index(stmt, "=")
+    expr = substr(stmt, eqp + 1)
+    VARS[vname] = expreval(expr)
+  }
+}
+
+function do_IF(stmt,  ropos, roend, relop, thenpos, rest, restpos, kw, expr1, expr2, r1, r2, c, k) {
+  ropos = index(stmt, "<")
+  r1 = index(stmt, ">")
+  r2 = index(stmt, "=")
+  if(ropos == 0 || (r1 > 0 && r1 < ropos)) ropos = r1
+  if(ropos == 0 || (r2 > 0 && r2 < ropos)) ropos = r2
+  roend = ropos
+  c = substr(stmt, ropos + 1, 1)
+  if(c == ">" || c == "<" || c == "=") roend++
+  relop = substr(stmt, ropos, roend - ropos + 1)
+  expr1 = substr(stmt, 1, ropos - 1)
+  rest = substr(stmt, roend + 1)
+  thenpos = 0
+  for(k=1; k<=10; k++) {
+    kw = IF_KWS[k]
+    thenpos = index(toupper(rest), kw)
+    if(thenpos > 0) {
+      if(kw == "=") thenpos--
+      restpos = thenpos
+      if(kw == "THEN") restpos += 4
+      break
+    } 
+  }
+  expr2 = substr(rest, 1, thenpos-1)
+  rest = substr(rest, restpos)
+  r1 = expreval(expr1)
+  r2 = expreval(expr2)
+  c = 0
+  if(relop == "<>" || relop == "><") c = (r1 != r2) ? 1 : 0
+  if(relop == "=" || relop == "==") c = (r1 == r2) ? 1 : 0
+  if(relop == ">") c = (r1 > r2) ? 1 : 0
+  if(relop == "<") c = (r1 < r2) ? 1 : 0
+  if(relop == ">=") c = (r1 >= r2) ? 1 : 0
+  if(relop == "<=") c = (r1 <= r2) ? 1 : 0
+  if(c == 1) proginput(rest)
+}
+
+function do_IN(stmt,  v, i, l) {
+  gsub("[[:space:]]+", "", stmt)
+  l = split(stmt, varlist, ",")
+  printf "? "
+  inputstr = ttyinput()
+  gsub("[[:space:]]+", "", inputstr)
+  split(toupper(inputstr), inputlist, ",")
+  for(i=1;i<=l;i++) {
+    v = toupper(substr(varlist[i], 1, 1))
+    VARS[v] = expreval(inputlist[i])
+  }
+}
+
+function do_PR(stmt,  item, quoting, c, l, i) {
+  item = ""
+  split("", printlist)
+  quoting = 0
+  l = length(stmt)
+  for(i=0;i<l;i++) {
+    c = substr(stmt, i+1, 1)
+    if(c == "\"") {
+      quoting = 1 - quoting
+      item = item c
+    } else if(quoting == 1) {item = item c}
+    else {
+      if(c == "," || c == ";") {
+        if(length(item) > 0) {stackpush(printlist, item); item = ""}
+        stackpush(printlist, c)
+      } else if(c != " " && c != "\t" && c != "\r") item = item c        
+    }
+  }
+  if(length(item) > 0) {stackpush(printlist, item); item = ""}
+  l = alen(printlist)
+  for(i=0;i<l;i++) {
+    item = printlist[i]
+    if(substr(item, 1, 1) == "\"") { # verbatim output
+      gsub(/^"|"$/, "", item)
+      printf("%s", item)
+    } else if(item == ",") printf("\t")
+    else if(item != ";") printf("%d", expreval(item))
+  }
+  if(l == 0 || (printlist[l-1] != "," && printlist[l-1] != ";")) printf("\n")
+}
+
+function do_EN(stmt) {IP = -1; split("", CALLSTACK)}
+
+# Program line execution function
+function progexec(stmt,  kw, ws, body) {
+  kw = toupper(substr(stmt, 1, 2))
+  if(substr(kw, 2, 1) == "=") {
+    kw = "LE"
+    stmt = "LE " stmt
+  }
+  if(kw == "LE" || kw == "GO" || kw =="IF" || kw == "IN" || kw == "PR" || kw == "RE" || kw == "EN") {
+    ws = index(stmt, " ")
+    if(ws < 1) ws = index(stmt, "\t")
+    if(ws > 0) body = wstrim(substr(stmt, ws))
+    else body = ""
+    if(kw == "GO") {
+      if(substr(toupper(stmt), 3, 1) == "S") do_GOS(body)
+      else do_GO(body)
+    } else if(kw == "LE") do_LE(body)
+    else if(kw == "IF") do_IF(body)
+    else if(kw == "IN") do_IN(body)
+    else if(kw == "PR") do_PR(body)
+    else if(kw == "RE") do_RE(body)
+    else if(kw == "EN") do_EN(body)
+  }
+}
+
+# Program line input function
+function proginput(stmt,  lno, i, l, c) {
+  l = length(stmt)
+  if(l == 0) return
+  lno = 0
+  for(i=0;i<l;i++) {
+    c = substr(stmt, i+1, 1)
+    if(c == int(c)) lno = lno * 10 + c
+    else if(c != " " && c != "\t") break
+  }
+  stmt = substr(stmt, i+1)
+  if(lno > 0) PROGMEM[lno] = stmt
+  else if(index(toupper(stmt), "REM") != 1) progexec(stmt)
+}
+
+# Clearing action
+function ext_CLEAR(i) {
+  split("", PROGMEM) # init program memory
+  split("", CALLSTACK) # init call stack array
+  split("", VARS) # init vars associative array
+  for(i=0;i<26;i++) VARS[sprintf("%c", 65+i)] = 0
+  IP = 0 # instruction pointer
+}
+
+function ext_LOAD(fname,    err, s) {
+  ext_CLEAR()
+  err = (getline s < fname)
+  if(err < 0) {
+    print "Error: File " fname " does not exist or cannot be read."
+    return
+  }
+  if(err > 0) proginput(wstrim(s))
+  while((getline s < fname) > 0) proginput(wstrim(s))
+  close(fname)
+}
+
+function ext_LIST(fname,  i, sep) {
+  fmt = (fname == "") ? "%d\t%s\n" : "%d %s\n"
+  for(i = 1; i > 0 && i < 32768; i++)
+    if(i in PROGMEM && length(PROGMEM[i]) > 0) {
+      if(fname == "") printf(fmt, i, PROGMEM[i])
+      else printf(fmt, i, PROGMEM[i]) >> fname
+    }
+  if(fname != "") {
+    fflush(fname)
+    close(fname)
+  }
+}
+
+function ext_RUN() {
+  for(IP = 1; IP > 0 && IP < 32768; IP++)
+    if(IP in PROGMEM && length(PROGMEM[IP]) > 0 && index(toupper(PROGMEM[IP]), "REM") != 1)
+      progexec(PROGMEM[IP])
+}
+
+# Init actions
+BEGIN {
+  srand() # init the PRNG
+  split("THEN IF LET = RETURN GOSUB INPUT PRINT GOTO END", IF_KWS)
+  ext_CLEAR() # init the memory
+  # print the welcome banner
+  print "-----------------------------"
+  print " Luxferre's Truly Tiny BASIC"
+  print "        AWK Edition"
+  print "      @ Copyleft 2026"
+  print "    All wrongs reserved"
+  print "-----------------------------"
+  if(ARGC > 1) {
+    printf "Preloading LTTB program from %s...\n", ARGV[1]
+    ext_LOAD(ARGV[1])
+  }
+  exit
+}
+
+# Main interpreter loop
+END {
+  while(1) {
+    printf "> "
+    cmd = wstrim(ttyinput())
+    if(length(cmd) > 0) {
+      if(toupper(cmd) == "BYE") {print "Bye!"; break}
+      else if(toupper(cmd) == "RUN") ext_RUN()
+      else if(toupper(cmd) == "LIST") ext_LIST("")
+      else if(toupper(cmd) == "NEW" || toupper(cmd) == "CLEAR") ext_CLEAR()
+      else if(toupper(cmd) == "LOAD") {
+        printf "File name: "
+        ext_LOAD(ttyinput())
+      }
+      else if(toupper(cmd) == "SAVE") {
+        printf "File name: "
+        ext_LIST(ttyinput())
+      }
+      else proginput(cmd) # pass as the program input
+    }
+  }
+}