Add rpn command

djpianalto.com/goff/exts/fun.go

@@ -2,8 +2,10 @@ package exts
 
 import (
 	"fmt"
-	"github.com/dustinpianalto/disgoman"
 	"strconv"
+
+	"djpianalto.com/goff/djpianalto.com/goff/utils"
+	"github.com/dustinpianalto/disgoman"
 )
 
 func interleave(ctx disgoman.Context, args []string) {
@@ -47,3 +49,11 @@ func deinterleave(ctx disgoman.Context, args []string) {
 		ctx.Send(fmt.Sprintf("(%v, %v)", x, y))
 	}
 }
+
+func rpn(ctx disgoman.Context, args []string) {
+	rpn, err := utils.GenerateRPN(args)
+	if err != nil {
+		ctx.Send(err.Error())
+	}
+	ctx.Send(rpn)
+}

djpianalto.com/goff/exts/init.go

@@ -186,4 +186,13 @@ func AddCommandHandlers(h *disgoman.CommandManager) {
 		RequiredPermissions: 0,
 		Invoke:              deinterleave,
 	})
+	_ = h.AddCommand(&disgoman.Command{
+		Name:                "rpn",
+		Aliases:             []string{"d"},
+		Description:         "Convert infix to rpn",
+		OwnerOnly:           false,
+		Hidden:              false,
+		RequiredPermissions: 0,
+		Invoke:              rpn,
+	})
 }

djpianalto.com/goff/utils/rpn.go

@@ -0,0 +1,156 @@
+package utils
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type Operator struct {
+	Token       string
+	Precedence  int
+	Association string
+}
+
+func (o Operator) HasHigherPrecedence(t Operator) bool {
+	return o.Precedence < t.Precedence // lower number is higher precedence
+}
+
+func (o Operator) HasEqualPrecedence(t Operator) bool {
+	return o.Precedence == t.Precedence
+}
+
+func (o Operator) IsLeftAssociative() bool {
+	return o.Association == "left"
+}
+
+var operators = map[string]Operator{
+	"+": Operator{
+		Token:       "+",
+		Precedence:  4,
+		Association: "left",
+	},
+	"-": Operator{
+		Token:       "-",
+		Precedence:  4,
+		Association: "left",
+	},
+	"*": Operator{
+		Token:       "*",
+		Precedence:  3,
+		Association: "left",
+	},
+	"/": Operator{
+		Token:       "/",
+		Precedence:  3,
+		Association: "left",
+	},
+	"%": Operator{
+		Token:       "%",
+		Precedence:  3,
+		Association: "left",
+	},
+	"(": Operator{
+		Token:       "(",
+		Precedence:  1,
+		Association: "left",
+	},
+	")": Operator{
+		Token:       ")",
+		Precedence:  1,
+		Association: "left",
+	},
+}
+
+type Stack []Operator
+
+func (s *Stack) IsEmpty() bool {
+	return len(*s) == 0
+}
+
+func (s *Stack) Push(op Operator) {
+	*s = append(*s, op)
+}
+
+func (s *Stack) Pop() (Operator, bool) {
+	if s.IsEmpty() {
+		return Operator{}, false
+	}
+	index := len(*s) - 1
+	element := (*s)[index]
+	*s = (*s)[:index]
+	return element, true
+}
+
+func (s *Stack) Top() Operator {
+	if s.IsEmpty() {
+		return Operator{}
+	}
+	return (*s)[len(*s)-1]
+}
+
+func GenerateRPN(tokens []string) (string, error) {
+	output := ""
+	s := Stack{}
+	for _, token := range tokens {
+		err := processToken(token, &s, &output)
+		if err != nil {
+			return "", err
+		}
+	}
+	for !s.IsEmpty() {
+		ele, _ := s.Pop()
+		output += " " + ele.Token
+	}
+
+	return strings.TrimSpace(output), nil
+}
+
+func processToken(t string, s *Stack, o *string) error {
+	if _, err := strconv.Atoi(t); err == nil {
+		*o += " " + t
+		return nil
+	} else if op, ok := operators[t]; ok {
+		if op.Token == "(" {
+			s.Push(op)
+		} else if op.Token == ")" {
+			if s.IsEmpty() {
+				return fmt.Errorf("mismatched parentheses")
+			}
+			for s.Top().Token != "(" {
+				if ele, ok := s.Pop(); ok {
+					*o += " " + ele.Token
+				} else {
+					return fmt.Errorf("mismatched parentheses")
+				}
+				if s.IsEmpty() {
+					break
+				}
+			}
+			s.Pop() // Pop and discard the (
+		} else if !s.IsEmpty() {
+			for {
+				if (s.Top().HasHigherPrecedence(op) ||
+					(s.Top().HasEqualPrecedence(op) &&
+						op.IsLeftAssociative())) &&
+					s.Top().Token != "(" {
+					if ele, ok := s.Pop(); ok {
+						*o += " " + ele.Token
+						if s.IsEmpty() {
+							break
+						}
+						continue
+					} else {
+						break
+					}
+				}
+				break
+			}
+			s.Push(op)
+		} else {
+			s.Push(op)
+		}
+		return nil
+	}
+	return fmt.Errorf("invalid character %s", t)
+}