first commit

1 files changed, 51 insertions, 0 deletions

diff --git a/evaluator.go b/evaluator.go
new file mode 100644
index 0000000..486d45f
--- /dev/null
+++ b/evaluator.go
@@ -0,0 +1,51 @@
+package expression
+
+import (
+	"go/scanner"
+	"go/token"
+)
+
+type Evaluator struct {
+	operators map[token.Token]Operator
+	functions map[string]func(stack *Stack) error
+}
+
+func New() *Evaluator {
+	return &Evaluator{
+		operators: DefaultOperators,
+		functions: DefaultFunctions,
+	}
+}
+
+func (e *Evaluator) Eval(expression string) (any, error) {
+	s := scanner.Scanner{}
+	fset := token.NewFileSet()
+	file := fset.AddFile("", fset.Base(), len(expression))
+	s.Init(file, []byte(expression), nil, scanner.ScanComments)
+	tokens := make(chan Token)
+	go func() {
+		for {
+			pos, tok, lit := s.Scan()
+			if tok == token.SEMICOLON {
+				continue
+			}
+			if tok == token.EOF {
+				break
+			}
+			tokens <- Token{
+				Token:   tok,
+				Literal: lit,
+				Pos:     int(pos),
+			}
+		}
+		close(tokens)
+	}()
+	rpnTokens := e.ToPRN(tokens)
+	return e.execute(rpnTokens)
+}
+
+type Operator struct {
+	fn          func(stack *Stack) error
+	priority    int
+	isLeftAssoc bool
+}