X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=src%2Fforth.jl;h=4b625bc146eb19cbcc36a51f6ab414789726645d;hb=03de266dbc3975cfa2f3b07de2d58ff642f4bf76;hp=9da680c832abe82466e4c5bea4d0444a00c8904d;hpb=d9652f786f96bb109ea03582db138816db0f8fda;p=forth.jl.git

diff --git a/src/forth.jl b/src/forth.jl
index 9da680c..4b625bc 100644
--- a/src/forth.jl
+++ b/src/forth.jl
@@ -31,6 +31,7 @@ size_TIB = 1096  # Terminal input buffer size
 
 mem = Array{Int64,1}(size_mem)
 primitives = Array{Function,1}()
+primNames = Array{ASCIIString,1}()
 
 # Built-in variables
 
@@ -101,6 +102,13 @@ function popPS()
     return val
 end
 
+# Handy functions for adding/retrieving strings to/from memory.
+
+getString(addr::Int64, len::Int64) = ASCIIString([Char(c) for c in mem[addr:(addr+len-1)]])
+function putString(str::ASCIIString, addr::Int64)
+    mem[addr:(addr+length(str)-1)] = [Int64(c) for c in str]
+end
+
 # Primitive creation and calling functions
 
 function createHeader(name::AbstractString, flags::Int64)
@@ -109,17 +117,20 @@ function createHeader(name::AbstractString, flags::Int64)
     mem[HERE] += 1
 
     mem[mem[HERE]] = length(name) | flags; mem[HERE] += 1
-    mem[mem[HERE]:(mem[HERE]+length(name)-1)] = [Int(c) for c in name]; mem[HERE] += length(name)
+    putString(name, mem[HERE]); mem[HERE] += length(name)
 end
 
 function defPrim(name::AbstractString, f::Function; flags::Int64=0)
     createHeader(name, flags)
 
+    codeWordAddr = mem[HERE]
     push!(primitives, f)
-    mem[mem[HERE]] = -length(primitives)
+    mem[codeWordAddr] = -length(primitives)
     mem[HERE] += 1
 
-    return -length(primitives)
+    push!(primNames, name)
+
+    return codeWordAddr
 end
 
 callPrim(addr::Int64) = primitives[-addr]()
@@ -127,29 +138,30 @@ callPrim(addr::Int64) = primitives[-addr]()
 function defExistingVar(name::AbstractString, varAddr::Int64; flags::Int64=0)
     defPrim(name, eval(:(() -> begin
         pushPS($(varAddr))
-        return NEXT
+        return mem[NEXT]
     end)))
 end
 
 function defNewVar(name::AbstractString, initial::Int64; flags::Int64=0)
     createHeader(name, flags)
     
+    codeWordAddr = mem[HERE]
     varAddr = mem[HERE] + 1
     push!(primitives, eval(:(() -> begin
         pushPS($(varAddr))
-        return NEXT
+        return mem[NEXT]
     end)))
     mem[mem[HERE]] = -length(primitives); mem[HERE] += 1
 
     mem[mem[HERE]] = initial; mem[HERE] += 1
 
-    return varAddr
+    return varAddr, codeWordAddr
 end
 
 function defConst(name::AbstractString, val::Int64; flags::Int64=0)
     defPrim(name, eval(:(() -> begin
         pushPS($(val))
-        return NEXT
+        return mem[NEXT]
     end)))
 
     return val
@@ -159,7 +171,7 @@ function defWord(name::AbstractString, wordAddrs::Array{Int64,1}; flags::Int64=0
     createHeader(name, flags)
 
     addr = mem[HERE]
-    mem[mem[HERE]] = DOCOL
+    mem[mem[HERE]] = mem[DOCOL]
     mem[HERE] += 1
 
     for wordAddr in wordAddrs
@@ -170,32 +182,30 @@ function defWord(name::AbstractString, wordAddrs::Array{Int64,1}; flags::Int64=0
     return addr
 end
 
-# Threading Primitives
+# Threading Primitives (inner interpreter)
 
 NEXT = defPrim("NEXT", () -> begin
     reg.W = mem[reg.IP]
     reg.IP += 1
-    X = mem[reg.W]
-    return X
+    return mem[reg.W]
 end)
 
 DOCOL = defPrim("DOCOL", () -> begin
     pushRS(reg.IP)
     reg.IP = reg.W + 1
-    return NEXT
+    return mem[NEXT]
 end)
 
 EXIT = defPrim("EXIT", () -> begin
     reg.IP = popRS()
-    return NEXT
+    return mem[NEXT]
 end)
 
-
 # Basic forth primitives
 
 DROP = defPrim("DROP", () -> begin
     popPS()
-    return NEXT
+    return mem[NEXT]
 end)
 
 SWAP = defPrim("SWAP", () -> begin
@@ -203,18 +213,18 @@ SWAP = defPrim("SWAP", () -> begin
     b = popPS()
     pushPS(a)
     pushPS(b)
-    return NEXT
+    return mem[NEXT]
 end)
 
 DUP = defPrim("DUP", () -> begin
     pushPS(mem[reg.PSP])
-    return NEXT
+    return mem[NEXT]
 end)
 
 OVER = defPrim("OVER", () -> begin
     ensurePSDepth(2)
     pushPS(mem[reg.PSP-1])
-    return NEXT
+    return mem[NEXT]
 end)
 
 ROT = defPrim("ROT", () -> begin
@@ -224,7 +234,7 @@ ROT = defPrim("ROT", () -> begin
     pushPS(a)
     pushPS(c)
     pushPS(b)
-    return NEXT
+    return mem[NEXT]
 end)
 
 NROT = defPrim("-ROT", () -> begin
@@ -234,13 +244,13 @@ NROT = defPrim("-ROT", () -> begin
     pushPS(b)
     pushPS(a)
     pushPS(c)
-    return NEXT
+    return mem[NEXT]
 end)
 
 TWODROP = defPrim("2DROP", () -> begin
     popPS()
     popPS()
-    return NEXT
+    return mem[NEXT]
 end)
 
 TWODUP = defPrim("2DUP", () -> begin
@@ -249,7 +259,7 @@ TWODUP = defPrim("2DUP", () -> begin
     b = mem[reg.PSP]
     pushPS(a)
     pushPS(b)
-    return NEXT
+    return mem[NEXT]
 end)
 
 TWOSWAP = defPrim("2SWAP", () -> begin
@@ -261,7 +271,7 @@ TWOSWAP = defPrim("2SWAP", () -> begin
     pushPS(a)
     pushPS(c)
     pushPS(d)
-    return NEXT
+    return mem[NEXT]
 end)
 
 QDUP = defPrim("?DUP", () -> begin
@@ -270,55 +280,167 @@ QDUP = defPrim("?DUP", () -> begin
     if val != 0
         pushPS(val)
     end
-    return NEXT
+    return mem[NEXT]
 end)
 
 INCR = defPrim("1+", () -> begin
     ensurePSDepth(1)
     mem[reg.PSP] += 1
-    return NEXT
+    return mem[NEXT]
 end)
 
 DECR = defPrim("1-", () -> begin
     ensurePSDepth(1)
     mem[reg.PSP] -= 1
-    return NEXT
+    return mem[NEXT]
+end)
+
+INCR2 = defPrim("2+", () -> begin
+    ensurePSDepth(1)
+    mem[reg.PSP] += 2
+    return mem[NEXT]
+end)
+
+DECR2 = defPrim("2-", () -> begin
+    ensurePSDepth(1)
+    mem[reg.PSP] -= 2
+    return mem[NEXT]
 end)
 
 ADD = defPrim("+", () -> begin
-    a = popPS()
     b = popPS()
+    a = popPS()
     pushPS(a+b)
-    return NEXT
+    return mem[NEXT]
 end)
 
 SUB = defPrim("-", () -> begin
-    a = popPS()
     b = popPS()
-    pushPS(b-a)
-    return NEXT
+    a = popPS()
+    pushPS(a-b)
+    return mem[NEXT]
 end)
 
 MUL = defPrim("*", () -> begin
-    a = popPS()
     b = popPS()
+    a = popPS()
     pushPS(a*b)
-    return NEXT
+    return mem[NEXT]
 end)
 
 DIVMOD = defPrim("/MOD", () -> begin
-    a = popPS()
     b = popPS()
-    q,r = divrem(b,a)
+    a = popPS()
+    q,r = divrem(a,b)
     pushPS(r)
     pushPS(q)
-    return NEXT
+    return mem[NEXT]
+end)
+
+EQU = defPrim("=", () -> begin
+    b = popPS()
+    a = popPS()
+    pushPS(a==b ? -1 : 0)
+    return mem[NEXT]
+end)
+
+NEQU = defPrim("<>", () -> begin
+    b = popPS()
+    a = popPS()
+    pushPS(a!=b ? -1 : 0)
+    return mem[NEXT]
 end)
 
+LT = defPrim("<", () -> begin
+    b = popPS()
+    a = popPS()
+    pushPS(a<b ? -1 : 0)
+    return mem[NEXT]
+end)
+
+GT = defPrim(">", () -> begin
+    b = popPS()
+    a = popPS()
+    pushPS(a>b ? -1 : 0)
+    return mem[NEXT]
+end)
+
+LE = defPrim("<=", () -> begin
+    b = popPS()
+    a = popPS()
+    pushPS(a<=b ? -1 : 0)
+    return mem[NEXT]
+end)
+
+GE = defPrim(">=", () -> begin
+    b = popPS()
+    a = popPS()
+    pushPS(a>=b ? -1 : 0)
+    return mem[NEXT]
+end)
+
+ZEQU = defPrim("0=", () -> begin
+    pushPS(popPS() == 0 ? -1 : 0)
+    return mem[NEXT]
+end)
+
+ZNEQU = defPrim("0<>", () -> begin
+    pushPS(popPS() != 0 ? -1 : 0)
+    return mem[NEXT]
+end)
+
+ZLT = defPrim("0<", () -> begin
+    pushPS(popPS() < 0 ? -1 : 0)
+    return mem[NEXT]
+end)
+
+ZGT = defPrim("0>", () -> begin
+    pushPS(popPS() > 0 ? -1 : 0)
+    return mem[NEXT]
+end)
+
+ZLE = defPrim("0<=", () -> begin
+    pushPS(popPS() <= 0 ? -1 : 0)
+    return mem[NEXT]
+end)
+
+ZGE = defPrim("0>=", () -> begin
+    pushPS(popPS() >= 0 ? -1 : 0)
+    return mem[NEXT]
+end)
+
+AND = defPrim("AND", () -> begin
+    b = popPS()
+    a = popPS()
+    pushPS(a & b)
+    return mem[NEXT]
+end)
+
+OR = defPrim("OR", () -> begin
+    b = popPS()
+    a = popPS()
+    pushPS(a | b)
+    return mem[NEXT]
+end)
+
+XOR = defPrim("XOR", () -> begin
+    b = popPS()
+    a = popPS()
+    pushPS(a $ b)
+    return mem[NEXT]
+end)
+
+INVERT = defPrim("INVERT", () -> begin
+    pushPS(~popPS())
+    return mem[NEXT]
+end)
+
+# Literals
+
 LIT = defPrim("LIT", () -> begin
     pushPS(mem[reg.IP])
     reg.IP += 1
-    return NEXT
+    return mem[NEXT]
 end)
 
 # Memory primitives
@@ -327,38 +449,38 @@ STORE = defPrim("!", () -> begin
     addr = popPS()
     dat = popPS()
     mem[addr] = dat
-    return NEXT
+    return mem[NEXT]
 end)
 
 FETCH = defPrim("@", () -> begin
     addr = popPS()
     pushPS(mem[addr])
-    return NEXT
+    return mem[NEXT]
 end)
 
 ADDSTORE = defPrim("+!", () -> begin
     addr = popPS()
     toAdd = popPS()
     mem[addr] += toAdd
-    return NEXT
+    return mem[NEXT]
 end)
 
 SUBSTORE = defPrim("-!", () -> begin
     addr = popPS()
     toSub = popPS()
     mem[addr] -= toSub
-    return NEXT
+    return mem[NEXT]
 end)
 
 
 # Built-in variables
 
-defExistingVar("HERE", HERE)
-defExistingVar("LATEST", LATEST)
-defExistingVar("PSP0", PSP0)
-defExistingVar("RSP0", RSP0)
-STATE = defNewVar("STATE", 0)
-BASE = defNewVar("BASE", 10)
+HERE_CFA = defExistingVar("HERE", HERE)
+LATEST_CFA = defExistingVar("LATEST", LATEST)
+PSP0_CFA = defExistingVar("PSP0", PSP0)
+RSP0_CFA = defExistingVar("RSP0", RSP0)
+STATE, STATE_CFA = defNewVar("STATE", 0)
+BASE, BASE_CFA = defNewVar("BASE", 10)
 
 # Constants
 
@@ -373,64 +495,64 @@ F_LENMASK = defConst("F_LENMASK", 127)
 
 TOR = defPrim(">R", () -> begin
     pushRS(popPS())
-    return NEXT
+    return mem[NEXT]
 end)
 
 FROMR = defPrim("R>", () -> begin
     pushPS(popRS())
-    return NEXT
+    return mem[NEXT]
 end)
 
 RSPFETCH = defPrim("RSP@", () -> begin
     pushPS(reg.RSP)
-    return NEXT
+    return mem[NEXT]
 end)
 
 RSPSTORE = defPrim("RSP!", () -> begin
     RSP = popPS()
-    return NEXT
+    return mem[NEXT]
 end)
 
 RDROP = defPrim("RDROP", () -> begin
     popRS()
-    return NEXT
+    return mem[NEXT]
 end)
 
 # Parameter Stack
 
 PSPFETCH = defPrim("PSP@", () -> begin
     pushPS(reg.PSP)
-    return NEXT
+    return mem[NEXT]
 end)
 
 PSPSTORE = defPrim("PSP!", () -> begin
     PSP = popPS()
-    return NEXT
+    return mem[NEXT]
 end)
 
 # I/O
 
 defConst("TIB", TIB)
-NUMTIB = defNewVar("#TIB", 0)
-TOIN = defNewVar(">IN", 0)
+NUMTIB, NUMTIB_CFA = defNewVar("#TIB", 0)
+TOIN, TOIN_CFA = defNewVar(">IN", 0)
 
 KEY = defPrim("KEY", () -> begin
     if mem[TOIN] >= mem[NUMTIB]
         mem[TOIN] = 0
         line = readline()
         mem[NUMTIB] = length(line)
-        mem[TIB:(TIB+mem[NUMTIB]-1)] = [Int64(c) for c in collect(line)]
+        putString(line, TIB)
     end
 
     pushPS(mem[TIB + mem[TOIN]])
     mem[TOIN] += 1
 
-    return NEXT
+    return mem[NEXT]
 end)
 
 EMIT = defPrim("EMIT", () -> begin
     print(Char(popPS()))
-    return NEXT
+    return mem[NEXT]
 end)
 
 WORD = defPrim("WORD", () -> begin
@@ -440,7 +562,7 @@ WORD = defPrim("WORD", () -> begin
     skip_to_end = false
     while true
 
-        callPrim(KEY)
+        callPrim(mem[KEY])
         c = Char(popPS())
 
         if c == '\\'
@@ -465,14 +587,25 @@ WORD = defPrim("WORD", () -> begin
     wordAddr = mem[HERE]
     offset = 0
 
+    if c == '\n'
+        # Treat newline as a special word
+
+        mem[wordAddr + offset] = Int64(c)
+        pushPS(wordAddr)
+        pushPS(1)
+        return mem[NEXT]
+    end
+
     while true
         mem[wordAddr + offset] = Int64(c)
         offset += 1
 
-        callPrim(KEY)
+        callPrim(mem[KEY])
         c = Char(popPS())
 
         if c == ' ' || c == '\t' || c == '\n'
+            # Rewind KEY
+            mem[TOIN] -= 1
             break
         end
     end
@@ -482,7 +615,7 @@ WORD = defPrim("WORD", () -> begin
     pushPS(wordAddr)
     pushPS(wordLen)
 
-    return NEXT
+    return mem[NEXT]
 end)
 
 NUMBER = defPrim("NUMBER", () -> begin
@@ -490,7 +623,7 @@ NUMBER = defPrim("NUMBER", () -> begin
     wordLen = popPS()
     wordAddr = popPS()
 
-    s = ASCIIString([Char(c) for c in mem[wordAddr:(wordAddr+wordLen-1)]])
+    s = getString(wordAddr, wordLen)
 
     try
         pushPS(parse(Int64, s, mem[BASE]))
@@ -499,7 +632,7 @@ NUMBER = defPrim("NUMBER", () -> begin
         pushPS(1) # Error indication
     end
 
-    return NEXT
+    return mem[NEXT]
 end)
 
 # Dictionary searches
@@ -508,31 +641,31 @@ FIND = defPrim("FIND", () -> begin
 
     wordLen = popPS()
     wordAddr = popPS()
-    word = ASCIIString([Char(c) for c in mem[wordAddr:(wordAddr+wordLen-1)]])
+    word = lowercase(getString(wordAddr, wordLen))
 
-    latest = mem[LATEST]
+    latest = LATEST
     
-    while latest>0
+    i = 0
+    while (latest = mem[latest]) > 0
         lenAndFlags = mem[latest+1]
         len = lenAndFlags & F_LENMASK
         hidden = (lenAndFlags & F_HIDDEN) == F_HIDDEN
 
         if hidden || len != wordLen
-            latest = mem[latest]
             continue
         end
         
         thisAddr = latest+2
-        thisWord = ASCIIString([Char(c) for c in mem[thisAddr:(thisAddr+len-1)]])
+        thisWord = lowercase(getString(thisAddr, len))
 
-        if thisWord == word
+        if lowercase(thisWord) == lowercase(word)
             break
         end
     end
 
     pushPS(latest)
 
-    return NEXT
+    return mem[NEXT]
 end)
 
 TOCFA = defPrim(">CFA", () -> begin
@@ -543,39 +676,247 @@ TOCFA = defPrim(">CFA", () -> begin
 
     pushPS(addr + 2 + len)
 
-    return NEXT
+    return mem[NEXT]
 end)
 
 TODFA = defWord(">DFA", [TOCFA, INCR, EXIT])
 
+# Compilation
+
+CREATE = defPrim("CREATE", () -> begin
+
+    wordLen = popPS()
+    wordAddr = popPS()
+    word = getString(wordAddr, wordLen)
+
+    createHeader(word, 0)
+
+    return mem[NEXT]
+end)
+
+COMMA = defPrim(",", () -> begin
+    mem[mem[HERE]] = popPS()
+    mem[HERE] += 1
+
+    return mem[NEXT]
+end)
+
+LBRAC = defPrim("[", () -> begin
+    mem[STATE] = 0
+    return mem[NEXT]
+end, flags=F_IMMED)
+
+RBRAC = defPrim("]", () -> begin
+    mem[STATE] = 1
+    return mem[NEXT]
+end, flags=F_IMMED)
+
+HIDDEN = defPrim("HIDDEN", () -> begin
+    addr = popPS() + 1
+    mem[addr] = mem[addr] $ F_HIDDEN
+    return mem[NEXT]
+end)
+
+HIDE = defWord("HIDE",
+    [WORD,
+    FIND,
+    HIDDEN,
+    EXIT])
+
+COLON = defWord(":",
+    [WORD,
+    CREATE,
+    LIT, DOCOL, COMMA,
+    LATEST, FETCH, HIDDEN,
+    RBRAC,
+    EXIT])
+
+SEMICOLON = defWord(";",
+    [LIT, EXIT, COMMA,
+    LATEST, FETCH, HIDDEN,
+    LBRAC,
+    EXIT], flags=F_IMMED)
+
+IMMEDIATE = defPrim("IMMEDIATE", () -> begin
+    lenAndFlagsAddr = mem[LATEST] + 1
+    mem[lenAndFlagsAddr] = mem[lenAndFlagsAddr] $ F_IMMED
+    return mem[NEXT]
+end, flags=F_IMMED)
+
+TICK = defWord("'", [WORD, FIND, TOCFA, EXIT])
+
+# Branching
+
+BRANCH = defPrim("BRANCH", () -> begin
+    reg.IP += mem[reg.IP]
+    return mem[NEXT]
+end)
+
+ZBRANCH = defPrim("0BRANCH", () -> begin
+    if (popPS() == 0)
+        reg.IP += mem[reg.IP]
+    else
+        reg.IP += 1
+    end
+
+    return mem[NEXT]
+end)
+
+# Strings
+
+LITSTRING = defPrim("LITSTRING", () -> begin
+    len = mem[reg.IP]
+    reg.IP += 1
+    pushPS(reg.IP)
+    pushPS(len)
+    reg.IP += len
+
+    return mem[NEXT]
+end)
+
+TELL = defPrim("TELL", () -> begin
+    len = popPS()
+    addr = popPS()
+    str = getString(addr, len)
+    print(str)
+    return mem[NEXT]
+end)
+
+# Outer interpreter
+
+INTERPRET = defPrim("INTERPRET", () -> begin
+
+    callPrim(mem[WORD])
+
+    wordName = getString(mem[reg.PSP-1], mem[reg.PSP])
+    println("... ", replace(wordName, "\n", "\\n"), " ...")
+
+    callPrim(mem[TWODUP])
+    callPrim(mem[FIND])
+
+    wordAddr = mem[reg.PSP]
+
+
+    if wordAddr>0
+        # Word in dictionary
+
+        isImmediate = (mem[wordAddr+1] & F_IMMED) != 0
+        callPrim(mem[TOCFA])
+
+        callPrim(mem[ROT]) # get rid of extra copy of word string details
+        popPS()
+        popPS()
+
+        if mem[STATE] == 0 || isImmediate
+            # Execute!
+            return mem[popPS()]
+        else
+            # Append CFA to dictionary
+            callPrim(mem[COMMA])
+        end
+    else
+        # Not in dictionary, assume number
+
+        popPS()
+
+        callPrim(mem[NUMBER])
+
+        if popPS() != 0
+            println("Parse error at word: '$wordName'")
+            return mem[NEXT]
+        else
+        end
+
+        if mem[STATE] == 0
+            # Number already on stack!
+        else
+            # Append literal to dictionary
+            pushPS(LIT)
+            callPrim(mem[COMMA])
+            callPrim(mem[COMMA])
+        end
+    end
+
+    return mem[NEXT]
+end)
+
+QUIT = defWord("QUIT",
+    [RSP0_CFA, RSPSTORE,
+    INTERPRET,
+    BRANCH,-2])
+
+NL = defPrim("\n", () -> begin
+    if mem[STATE] == 0
+        println(" ok")
+    end
+    return mem[NEXT]
+end)
+
+# Odds and Ends
+
+CHAR = defPrim("CHAR", () -> begin
+    callPrim(mem[WORD])
+    wordLen = popPS()
+    wordAddr = popPS()
+    word = getString(wordAddr, wordLen)
+    pushPS(Int64(word[1]))
+
+    return mem[NEXT]
+end)
+
+EXECUTE = defPrim("EXECUTE", () -> begin
+    return mem[popPS()]
+end)
+
+BYE = defPrim("BYE", () -> begin
+    return 0
+end)
+
 #### VM loop ####
 function runVM()
-    jmp = NEXT
-    while (jmp = callPrim(jmp)) != 0 end
+    # Start with IP pointing to first instruction of outer interpreter
+    reg.IP = QUIT + 1
+
+    # Primitive processing loop.
+    # Everyting else is simply a consequence of this loop!
+    jmp = mem[NEXT]
+    while (jmp = callPrim(jmp)) != 0
+        println("Evaluating prim $jmp [$(primNames[-jmp])]")
+    end
 end
 
 # Debugging tools
 
-function coredump(startAddr::Int64; count::Int64 = 16, cellsPerLine::Int64 = 8)
+function dump(startAddr::Int64; count::Int64 = 100, cellsPerLine::Int64 = 10)
     chars = Array{Char,1}(cellsPerLine)
 
-    for i in 0:(count-1)
-        addr = startAddr + i
-        if i%cellsPerLine == 0
-            print("$addr:")
-        end
-
-        print("\t$(mem[addr]) ")
+    lineStartAddr = cellsPerLine*div((startAddr-1),cellsPerLine) + 1
+    endAddr = startAddr + count - 1
+
+    q, r = divrem((endAddr-lineStartAddr+1), cellsPerLine)
+    numLines = q + (r > 0 ? 1 : 0)
+
+    i = lineStartAddr
+    for l in 1:numLines
+        print(i,":")
+
+        for c in 1:cellsPerLine
+            if i >= startAddr && i <= endAddr
+                print("\t",mem[i])
+                if mem[i]>=32 && mem[i]<128
+                    chars[c] = Char(mem[i])
+                else
+                    chars[c] = '.'
+                end
+            else
+                print("\t")
+                chars[c] = ' '
+            end
 
-        if (mem[addr]>=32 && mem[addr]<176)
-            chars[i%cellsPerLine + 1] = Char(mem[addr])
-        else
-            chars[i%cellsPerLine + 1] = '.'
+            i += 1
         end
 
-        if i%cellsPerLine == cellsPerLine-1
-            println(string("\t", ASCIIString(chars)))
-        end
+        println("\t", ASCIIString(chars))
     end
 end
 
@@ -593,4 +934,18 @@ function printPS()
     end
 end
 
+function printRS()
+    count = reg.RSP - mem[RSP0]
+
+    if count > 0
+        print("<$count>")
+        for i in (mem[RSP0]+1):reg.RSP
+            print(" $(mem[i])")
+        end
+        println()
+    else
+        println("Return stack empty")
+    end
+end
+
 end