refactoring a bit, defined accumulator struct

added subtraction and multiplication

acc.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"fmt"
+	"reflect"
+)
+
+type accumulator struct {
+	name     string
+	floatFn  func(float64, float64) float64
+	intFn    func(int64, int64) int64
+	acc      int64
+	accf     float64
+	floating bool
+}
+
+func (a *accumulator) total(vals ...interface{}) (interface{}, error) {
+	if len(vals) == 0 {
+		return int64(0), nil
+	}
+
+	switch v := vals[0].(type) {
+	case int64:
+		a.acc = v
+	case float64:
+		a.floating = true
+		a.accf = v
+	default:
+		return nil, fmt.Errorf("%v is not defined for %v", a.name, reflect.TypeOf(v))
+	}
+
+	if len(vals) == 1 {
+		if a.floating {
+			return a.accf, nil
+		} else {
+			return a.acc, nil
+		}
+	}
+
+	for _, raw := range vals[1:] {
+		switch v := raw.(type) {
+		case int64:
+			if a.floating {
+				a.accf = a.floatFn(a.accf, float64(v))
+				break
+			}
+			a.acc = a.intFn(a.acc, v)
+		case float64:
+			if !a.floating {
+				a.floating = true
+				a.accf = a.floatFn(a.accf, float64(a.acc))
+			}
+			a.accf = a.floatFn(a.accf, v)
+		default:
+			return nil, fmt.Errorf("%v is not defined for %v", a.name, reflect.TypeOf(v))
+		}
+	}
+	if a.floating {
+		return a.accf, nil
+	} else {
+		return a.acc, nil
+	}
+	panic("not reached")
+}

proc.go

@@ -1,40 +1,42 @@
 package main
 
-import (
-	"fmt"
-	"reflect"
-)
-
 type proc func(...interface{}) (interface{}, error)
 
 func addition(vals ...interface{}) (interface{}, error) {
-	addFloats := false
-	var accf float64
-	var acc int64
+	a := accumulator{
+		name: "addition",
+		floatFn: func(left, right float64) float64 {
+			return left + right
+		},
+		intFn: func(left, right int64) int64 {
+			return left + right
+		},
+	}
+	return a.total(vals...)
+}
 
-	for _, raw := range vals {
-		switch v := raw.(type) {
-		case int64:
-			if addFloats {
-				accf += float64(v)
-			} else {
-				acc += v
-			}
-		case float64:
-			if !addFloats {
-				addFloats = true
-				accf += float64(acc)
-			}
-			accf += v
-		default:
-			return nil, fmt.Errorf("addition is not defined for %v", reflect.TypeOf(v))
-		}
+func subtraction(vals ...interface{}) (interface{}, error) {
+	a := accumulator{
+		name: "subtraction",
+		floatFn: func(left, right float64) float64 {
+			return left - right
+		},
+		intFn: func(left, right int64) int64 {
+			return left - right
+		},
 	}
+	return a.total(vals...)
+}
 
-	if addFloats {
-		return accf, nil
-	} else {
-		return acc, nil
+func multiplication(vals ...interface{}) (interface{}, error) {
+	a := accumulator{
+		name: "multiplication",
+		floatFn: func(left, right float64) float64 {
+			return left * right
+		},
+		intFn: func(left, right int64) int64 {
+			return left * right
+		},
 	}
-	panic("not reached")
+	return a.total(vals...)
 }

skeam.go

@@ -17,10 +17,12 @@ type sexp []interface{}
 type symbol string
 
 var universe = environment{
-	"int":    5,
-	"float":  3.14,
+	"int":    int64(5),
+	"float":  float64(3.14),
 	"string": "Jordan",
 	"+":      proc(addition),
+	"-":      proc(subtraction),
+	"*":      proc(multiplication),
 }
 
 // parses the string lexeme into a value that can be eval'd