From 87b17b0ee12c90f028186761fbb2bd5f6b4008eb Mon Sep 17 00:00:00 2001
From: Tim Vaughan <tgvaughan@gmail.com>
Date: Tue, 24 May 2016 00:48:59 +1200
Subject: [PATCH] RSP0 and PSP0 now constants.  Closes #4.

---
 README.md    |  5 ++---
 src/forth.jl | 35 +++++++++++++++++------------------
 src/lib.4th  |  4 ++--
 3 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/README.md b/README.md
index fd8da69..612de1a 100644
--- a/README.md
+++ b/README.md
@@ -44,13 +44,12 @@ the library file.  Once this is complete you can start entering forth commands:
 
 Notice that unlike other forths, forth.jl echos a newline after reading each
 line of standard input.  This is an unfortunate side-effect of the way that
-I've implemented the primitive word KEY.  Hopefully I'll be able to fix this
-in future.
+I've implemented EXPECT.  Hopefully I'll be able to fix this in future.
 
 There's an example Mandelbrot Set drawing program included in the examples
 directory.  To run it, you'll have to locate this directory on your system (its
 location depends on what OS you happen to be using and how julia is installed).
-Once found, use the "INCLUDE" word to compile its definitions. For example, on
+Once found, use the INCLUDE word to compile its definitions. For example, on
 my system I can run the example in this way:
 
     include /home/tim/.julia/v0.4/forth/examples/mandelbrot.4th
diff --git a/src/forth.jl b/src/forth.jl
index cdb56d5..fb7121c 100644
--- a/src/forth.jl
+++ b/src/forth.jl
@@ -36,16 +36,14 @@ primNames = Array{ASCIIString,1}()
 # Built-in variables
 
 nextVarAddr = 1
-RSP0 = nextVarAddr; nextVarAddr += 1
-PSP0 = nextVarAddr; nextVarAddr += 1
 HERE = nextVarAddr; nextVarAddr += 1
 LATEST = nextVarAddr; nextVarAddr += 1
 
-mem[RSP0] = nextVarAddr              # bottom of RS
-mem[PSP0] = mem[RSP0] + size_RS      # bottom of PS
-TIB = mem[PSP0] + size_PS            # address of terminal input buffer
-mem[HERE] = TIB + size_TIB           # location of bottom of dictionary
-mem[LATEST] = 0                      # no previous definition
+RSP0 = nextVarAddr                  # bottom of RS
+PSP0 = RSP0 + size_RS               # bottom of PS
+TIB = PSP0 + size_PS                # address of terminal input buffer
+mem[HERE] = TIB + size_TIB          # location of bottom of dictionary
+mem[LATEST] = 0                     # no previous definition
 
 DICT = mem[HERE] # Save bottom of dictionary as constant
 
@@ -56,7 +54,7 @@ type Reg
     IP::Int64   # Instruction pointer
     W::Int64    # Working register
 end
-reg = Reg(mem[RSP0], mem[PSP0], 0, 0)
+reg = Reg(RSP0, PSP0, 0, 0)
 
 # Stack manipulation functions
 
@@ -66,8 +64,8 @@ type ReturnStackUnderflow <: Exception end
 Base.showerror(io::IO, ex::ParamStackUnderflow) = print(io, "Parameter stack underflow.")
 Base.showerror(io::IO, ex::ReturnStackUnderflow) = print(io, "Return stack underflow.")
 
-getRSDepth() = reg.RSP - mem[RSP0]
-getPSDepth() = reg.PSP - mem[PSP0]
+getRSDepth() = reg.RSP - RSP0
+getPSDepth() = reg.PSP - PSP0
 
 function ensurePSDepth(depth::Int64)
     if getPSDepth()<depth
@@ -237,8 +235,9 @@ end)
 
 HERE_CFA = defExistingVar("HERE", HERE)
 LATEST_CFA = defExistingVar("LATEST", LATEST)
-PSP0_CFA = defExistingVar("PSP0", PSP0)
-RSP0_CFA = defExistingVar("RSP0", RSP0)
+
+PSP0_CFA = defConst("PSP0", PSP0)
+RSP0_CFA = defConst("RSP0", RSP0)
 
 defConst("DOCOL", DOCOL)
 defConst("DOCON", DOCON)
@@ -878,13 +877,13 @@ end)
 QUIT = defWord("QUIT",
     [LIT, 0, STATE_CFA, STORE,
     LIT, 0, NUMTIB_CFA, STORE,
-    RSP0_CFA, FETCH, RSPSTORE,
+    RSP0_CFA, RSPSTORE,
     QUERY,
     INTERPRET, PROMPT,
     BRANCH,-4])
 
 ABORT = defWord("ABORT",
-    [PSP0_CFA, FETCH, PSPSTORE, QUIT])
+    [PSP0_CFA, PSPSTORE, QUIT])
 
 INCLUDE = defPrimWord("INCLUDE", () -> begin
     pushPS(32)
@@ -1043,11 +1042,11 @@ function dump(startAddr::Int64; count::Int64 = 100, cellsPerLine::Int64 = 10)
 end
 
 function printPS()
-    count = reg.PSP - mem[PSP0]
+    count = reg.PSP - PSP0
 
     if count > 0
         print("<$count>")
-        for i in (mem[PSP0]+1):reg.PSP
+        for i in (PSP0+1):reg.PSP
             print(" $(mem[i])")
         end
         println()
@@ -1057,11 +1056,11 @@ function printPS()
 end
 
 function printRS()
-    count = reg.RSP - mem[RSP0]
+    count = reg.RSP - RSP0
 
     if count > 0
         print("<$count>")
-        for i in (mem[RSP0]+1):reg.RSP
+        for i in (RSP0+1):reg.RSP
             print(" $(mem[i])")
         end
         println()
diff --git a/src/lib.4th b/src/lib.4th
index 301f9ac..e258ea7 100644
--- a/src/lib.4th
+++ b/src/lib.4th
@@ -25,7 +25,7 @@
 : C@ @ ;
 : C, , ;
 
-: DEPTH PSP@ PSP0 @ - ;
+: DEPTH PSP@ PSP0 - ;
 
 : '\n' 10 ;
 : BL 32 ;
@@ -362,7 +362,7 @@
 
 : .S            ( -- )
         [CHAR] < EMIT DEPTH U. [CHAR] > EMIT SPACE
-        PSP0 @ 1+
+        PSP0 1+
         BEGIN
                 DUP PSP@ 2 - <=
         WHILE
-- 
2.20.1