From a75db93581d35578b0068a25349878fc137d1728 Mon Sep 17 00:00:00 2001
From: David Ashby <delta.mu.alpha@gmail.com>
Date: Sat, 20 Feb 2021 18:03:02 -0500
Subject: [PATCH] add more common math and fix my comparison checks

---
 builtins.go | 78 ++++++++++++++++++++++++++++++++++++++---------------
 main.go     |  6 +++++
 2 files changed, 63 insertions(+), 21 deletions(-)

diff --git a/builtins.go b/builtins.go
index fac4261..a5692b2 100644
--- a/builtins.go
+++ b/builtins.go
@@ -7,6 +7,9 @@ import (
 	"os"
 )
 
+var FALSE = 0
+var TRUE = -1
+
 // Builtins is a handy holder for our various default words
 type Builtins struct{}
 
@@ -61,10 +64,10 @@ func (b *Builtins) Eq(s *Stack) func() error {
 			return err
 		}
 		if tos == nos {
-			s.Push(-1)
+			s.Push(TRUE)
 			return nil
 		}
-		s.Push(0)
+		s.Push(FALSE)
 		return nil
 	}
 }
@@ -81,10 +84,10 @@ func (b *Builtins) NEq(s *Stack) func() error {
 			return err
 		}
 		if tos != nos {
-			s.Push(-1)
+			s.Push(TRUE)
 			return nil
 		}
-		s.Push(0)
+		s.Push(FALSE)
 		return nil
 	}
 }
@@ -100,11 +103,11 @@ func (b *Builtins) Lt(s *Stack) func() error {
 		if err != nil {
 			return err
 		}
-		if tos < nos {
-			s.Push(-1)
+		if nos < tos {
+			s.Push(TRUE)
 			return nil
 		}
-		s.Push(0)
+		s.Push(FALSE)
 		return nil
 	}
 }
@@ -120,11 +123,11 @@ func (b *Builtins) Gt(s *Stack) func() error {
 		if err != nil {
 			return err
 		}
-		if tos > nos {
-			s.Push(-1)
+		if nos > tos {
+			s.Push(TRUE)
 			return nil
 		}
-		s.Push(0)
+		s.Push(FALSE)
 		return nil
 	}
 }
@@ -140,11 +143,11 @@ func (b *Builtins) LtEq(s *Stack) func() error {
 		if err != nil {
 			return err
 		}
-		if tos <= nos {
-			s.Push(-1)
+		if nos <= tos {
+			s.Push(TRUE)
 			return nil
 		}
-		s.Push(0)
+		s.Push(FALSE)
 		return nil
 	}
 }
@@ -160,11 +163,11 @@ func (b *Builtins) GtEq(s *Stack) func() error {
 		if err != nil {
 			return err
 		}
-		if tos >= nos {
-			s.Push(-1)
+		if nos >= tos {
+			s.Push(TRUE)
 			return nil
 		}
-		s.Push(0)
+		s.Push(FALSE)
 		return nil
 	}
 }
@@ -233,6 +236,39 @@ func (b *Builtins) Div(s *Stack) func() error {
 	}
 }
 
+// Mod performs NOS%TOS and pushes the (integer!) modulo result
+func (b *Builtins) Mod(s *Stack) func() error {
+	return func() error {
+		tos, err := s.Pop()
+		if err != nil {
+			return err
+		}
+		nos, err := s.Pop()
+		if err != nil {
+			return err
+		}
+		s.Push(nos % tos)
+		return nil
+	}
+}
+
+// DivMod performs NOS/TOS & NOS%TOS and pushes the (integer!) results: TOS as quotient, NOS as remainder
+func (b *Builtins) DivMod(s *Stack) func() error {
+	return func() error {
+		tos, err := s.Pop()
+		if err != nil {
+			return err
+		}
+		nos, err := s.Pop()
+		if err != nil {
+			return err
+		}
+		s.Push(nos % tos)
+		s.Push(nos / tos)
+		return nil
+	}
+}
+
 // Print pops the stack and outputs it to the writer with a trailing space (defaults to stdout)
 func (b *Builtins) Print(out io.Writer, s *Stack) func() error {
 	if out == nil {
@@ -418,13 +454,13 @@ func (b *Builtins) If(s *Stack, i *Stack) func() error {
 		if err != nil {
 			return err
 		}
-		// TOS was 0, don't execute this branch
-		if tos == 0 {
+		// TOS was FALSE, don't execute this branch
+		if tos == FALSE {
 			i.Push(0)
-		} else {
-			// TOS wasn't 0, execute until we see ELSE/THEN
-			i.Push(1)
+			return nil
 		}
+		// TOS wasn't 0, execute until we see ELSE/THEN
+		i.Push(1)
 		return nil
 	}
 }
diff --git a/main.go b/main.go
index ecec366..d55857c 100644
--- a/main.go
+++ b/main.go
@@ -39,6 +39,11 @@ func main() {
 	dict.AddWord("-", Word{Name: "-", Impl: b.Sub(&stack)})
 	dict.AddWord("*", Word{Name: "*", Impl: b.Mul(&stack)})
 	dict.AddWord("/", Word{Name: "/", Impl: b.Div(&stack)})
+	dict.AddWord("MOD", Word{Name: "MOD", Impl: b.Mod(&stack)})
+	dict.AddWord("/MOD", Word{Name: "/MOD", Impl: b.DivMod(&stack)})
+	dict.AddWord("+1", Word{Name: "+1", Source: []string{"1", "+"}})
+	dict.AddWord("-1", Word{Name: "-1", Source: []string{"1", "-"}})
+	dict.AddWord("ABS", Word{Name: "ABS", Source: []string{"DUP 0< IF DUP DUP - SWAP - THEN"}})
 	// output
 	dict.AddWord(".", Word{Name: ".", Impl: b.Print(os.Stdout, &stack)})
 	dict.AddWord("EMIT", Word{Name: "EMIT", Impl: b.Emit(os.Stdout, &stack)})
@@ -47,6 +52,7 @@ func main() {
 	dict.AddWord("=", Word{Name: "=", Impl: b.Eq(&stack)})
 	dict.AddWord("0=", Word{Name: "0=", Source: []string{"0", "="}})
 	dict.AddWord("<>", Word{Name: "<>", Impl: b.NEq(&stack)})
+	dict.AddWord("0<>", Word{Name: "0<>", Source: []string{"0=", "0="}})
 	dict.AddWord(">", Word{Name: ">", Impl: b.Gt(&stack)})
 	dict.AddWord("<", Word{Name: "<", Impl: b.Lt(&stack)})
 	dict.AddWord(">=", Word{Name: ">=", Impl: b.GtEq(&stack)})