From cc4c01c69c238c92602b393ed87575ba5edad352 Mon Sep 17 00:00:00 2001
From: Alexander Kiryukhin <i@neonxp.dev>
Date: Fri, 1 Jul 2022 02:16:07 +0300
Subject: first commit

---
 infixrpn.go | 104 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 infixrpn.go

(limited to 'infixrpn.go')

diff --git a/infixrpn.go b/infixrpn.go
new file mode 100644
index 0000000..18dde39
--- /dev/null
+++ b/infixrpn.go
@@ -0,0 +1,104 @@
+package expression
+
+import (
+	"fmt"
+	"go/token"
+)
+
+func (e *Evaluator) ToPRN(in <-chan Token) chan Token {
+	out := make(chan Token)
+	stack := &Stack{}
+
+	go func() {
+		defer func() {
+			for !stack.Empty() {
+				tok := stack.Pop()
+				if tok.LP() {
+					out <- Token{
+						Token:   token.ILLEGAL,
+						Literal: "no closing parenthesis",
+						Pos:     tok.Pos,
+					}
+				} else {
+					out <- tok
+				}
+			}
+			close(out)
+		}()
+		for tok := range in {
+			switch {
+			case tok.Token == token.ILLEGAL:
+				return
+			case tok.IsNumber():
+				out <- tok
+			case tok.IsFunc():
+				stack.Push(tok)
+			case tok.IsSeparator():
+				for {
+					if stack.Empty() {
+						out <- Token{
+							Token:   token.ILLEGAL,
+							Literal: "no opening parenthesis",
+							Pos:     tok.Pos,
+						}
+						return
+					}
+					if stack.Head().LP() {
+						break
+					}
+					out <- tok
+				}
+			case tok.IsOperator():
+				op1 := e.operators[tok.Token]
+				for {
+					if stack.Empty() {
+						break
+					}
+					if stack.Head().IsOperator() {
+						op2, hasOp := e.operators[stack.Head().Token]
+						if !hasOp {
+							out <- Token{
+								Token:   token.ILLEGAL,
+								Literal: fmt.Sprintf("unknown operator: %s", stack.Head().Literal),
+								Pos:     tok.Pos,
+							}
+							return
+						}
+						if op2.priority > op1.priority {
+							out <- stack.Pop()
+							continue
+						} else {
+							break
+						}
+					} else {
+						break
+					}
+				}
+				stack.Push(tok)
+			case tok.LP():
+				stack.Push(tok)
+			case tok.RP():
+				for {
+					if stack.Empty() {
+						out <- Token{
+							Token:   token.ILLEGAL,
+							Literal: "no opening parenthesis",
+							Pos:     tok.Pos,
+						}
+						return
+					}
+					if stack.Head().LP() {
+						break
+					}
+					out <- tok
+				}
+				stack.Pop()
+				if stack.Head().IsFunc() {
+					out <- stack.Pop()
+				}
+			}
+		}
+	}()
+
+	return out
+}
-- 
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