diff --git a/core/cast.go b/core/cast.go
new file mode 100644
index 0000000..23a39d2
--- /dev/null
+++ b/core/cast.go
@@ -0,0 +1,81 @@
+package core
+
+import (
+	"github.com/mediocregopher/ginger/types"
+)
+
+func Int(e types.Elem) int {
+	return e.(types.GoType).V.(int)
+}
+
+func Int8(e types.Elem) int8 {
+	return e.(types.GoType).V.(int8)
+}
+
+func Int16(e types.Elem) int16 {
+	return e.(types.GoType).V.(int16)
+}
+
+func Int32(e types.Elem) int32 {
+	return e.(types.GoType).V.(int32)
+}
+
+func Int64(e types.Elem) int64 {
+	return e.(types.GoType).V.(int64)
+}
+
+func Uint(e types.Elem) uint {
+	return e.(types.GoType).V.(uint)
+}
+
+func Uint8(e types.Elem) uint8 {
+	return e.(types.GoType).V.(uint8)
+}
+
+func Uint16(e types.Elem) uint16 {
+	return e.(types.GoType).V.(uint16)
+}
+
+func Uint32(e types.Elem) uint32 {
+	return e.(types.GoType).V.(uint32)
+}
+
+func Uint64(e types.Elem) uint64 {
+	return e.(types.GoType).V.(uint64)
+}
+
+func Float32(e types.Elem) float32 {
+	return e.(types.GoType).V.(float32)
+}
+
+func Float64(e types.Elem) float64 {
+	return e.(types.GoType).V.(float64)
+}
+
+func Complex64(e types.Elem) complex64 {
+	return e.(types.GoType).V.(complex64)
+}
+
+func Complex128(e types.Elem) complex128 {
+	return e.(types.GoType).V.(complex128)
+}
+
+func Bool(e types.Elem) bool {
+	return e.(types.GoType).V.(bool)
+}
+
+func Byte(e types.Elem) byte {
+	return e.(types.GoType).V.(byte)
+}
+
+func Rune(e types.Elem) rune {
+	return e.(types.GoType).V.(rune)
+}
+
+func String(e types.Elem) string {
+	return e.(types.GoType).V.(string)
+}
+
+func Error(e types.Elem) error {
+	return e.(types.GoType).V.(error)
+}
diff --git a/core/math.go b/core/math.go
new file mode 100644
index 0000000..4c5c0f4
--- /dev/null
+++ b/core/math.go
@@ -0,0 +1,138 @@
+package core
+
+import (
+	"fmt"
+
+	"github.com/mediocregopher/ginger/seq"
+	"github.com/mediocregopher/ginger/types"
+)
+
+type mathReduceFn func(types.Elem, types.Elem) types.Elem
+
+func mathReduce(fn mathReduceFn, zero types.Elem, s seq.Seq) types.Elem {
+	reduceFn := func(acc, el types.Elem) (types.Elem, bool) {
+		return fn(acc, el), false
+	}
+	return seq.Reduce(reduceFn, zero, s)
+}
+
+func plusInt(a, b types.Elem) types.Elem {
+	return types.GoType{Int(a) + Int(b)}
+}
+
+func plusInt8(a, b types.Elem) types.Elem {
+	return types.GoType{Int8(a) + Int8(b)}
+}
+
+func plusInt16(a, b types.Elem) types.Elem {
+	return types.GoType{Int16(a) + Int16(b)}
+}
+
+func plusInt32(a, b types.Elem) types.Elem {
+	return types.GoType{Int32(a) + Int32(b)}
+}
+
+func plusInt64(a, b types.Elem) types.Elem {
+	return types.GoType{Int64(a) + Int64(b)}
+}
+
+func plusUint(a, b types.Elem) types.Elem {
+	return types.GoType{Uint(a) + Uint(b)}
+}
+
+func plusUint8(a, b types.Elem) types.Elem {
+	return types.GoType{Uint8(a) + Uint8(b)}
+}
+
+func plusUint16(a, b types.Elem) types.Elem {
+	return types.GoType{Uint16(a) + Uint16(b)}
+}
+
+func plusUint32(a, b types.Elem) types.Elem {
+	return types.GoType{Uint32(a) + Uint32(b)}
+}
+
+func plusUint64(a, b types.Elem) types.Elem {
+	return types.GoType{Uint64(a) + Uint64(b)}
+}
+
+func plusFloat32(a, b types.Elem) types.Elem {
+	return types.GoType{Float32(a) + Float32(b)}
+}
+
+func plusFloat64(a, b types.Elem) types.Elem {
+	return types.GoType{Float64(a) + Float64(b)}
+}
+
+func plusComplex64(a, b types.Elem) types.Elem {
+	return types.GoType{Complex64(a) + Complex64(b)}
+}
+
+func plusComplex128(a, b types.Elem) types.Elem {
+	return types.GoType{Complex128(a) + Complex128(b)}
+}
+
+func plusString(a, b types.Elem) types.Elem {
+	return types.GoType{String(a) + String(b)}
+}
+
+func Plus(s seq.Seq) types.Elem {
+	if seq.Empty(s) {
+		return types.GoType{0}
+	}
+
+	first, _, _ := s.FirstRest()
+	var fn mathReduceFn
+	var zero types.Elem
+	switch first.(types.GoType).V.(type) {
+	case int:
+		fn = plusInt
+		zero = types.GoType{int(0)}
+	case int8:
+		fn = plusInt8
+		zero = types.GoType{int8(0)}
+	case int16:
+		fn = plusInt16
+		zero = types.GoType{int16(0)}
+	case int32:
+		fn = plusInt32
+		zero = types.GoType{int32(0)}
+	case int64:
+		fn = plusInt64
+		zero = types.GoType{int64(0)}
+	case uint:
+		fn = plusInt
+		zero = types.GoType{uint(0)}
+	case uint8:
+		fn = plusInt8
+		zero = types.GoType{uint8(0)}
+	case uint16:
+		fn = plusInt16
+		zero = types.GoType{uint16(0)}
+	case uint32:
+		fn = plusInt32
+		zero = types.GoType{uint32(0)}
+	case uint64:
+		fn = plusInt64
+		zero = types.GoType{uint64(0)}
+	case float32:
+		fn = plusFloat32
+		zero = types.GoType{float32(0)}
+	case float64:
+		fn = plusFloat64
+		zero = types.GoType{float64(0)}
+	case complex64:
+		fn = plusComplex64
+		zero = types.GoType{complex64(0)}
+	case complex128:
+		fn = plusComplex128
+		zero = types.GoType{complex128(0)}
+	case string:
+		fn = plusString
+		zero = types.GoType{string(0)}
+	default:
+		panic(fmt.Sprintf("$#v cannot have plus called on it", first))
+	}
+
+	return mathReduce(fn, zero, s)
+}
diff --git a/eval/eval_test.go b/eval/eval_test.go
index 7888689..bc8d075 100644
--- a/eval/eval_test.go
+++ b/eval/eval_test.go
@@ -3,9 +3,9 @@ package eval
 import (
 	. "testing"
 
+	"github.com/mediocregopher/ginger/core"
 	"github.com/mediocregopher/ginger/macros/pkgctx"
 	"github.com/mediocregopher/ginger/parse"
-	"github.com/mediocregopher/ginger/seq"
 	"github.com/mediocregopher/ginger/types"
 )
 
@@ -13,27 +13,18 @@ import (
 // something down before I kept thinking about it, so I would know what would
 // work
 
-func shittyPlus(s seq.Seq) types.Elem {
-	fn := func(acc, el types.Elem) (types.Elem, bool) {
-		i := acc.(types.GoType).V.(int) + el.(types.GoType).V.(int)
-		return types.GoType{i}, false
-	}
-
-	return seq.Reduce(fn, types.GoType{0}, s)
-}
-
 func TestShittyPlus(t *T) {
 	p := &pkgctx.PkgCtx{
 		CallMap: map[string]interface{}{
-			"shittyPlus": Evaler(shittyPlus),
+			"Plus": Evaler(core.Plus),
 		},
 	}
 
 	m := map[string]types.Elem{
-		"(: shittyPlus)":       types.GoType{0},
-		"(: shittyPlus 1 2 3)": types.GoType{6},
-		`(: shittyPlus 1 2 3
-			(: shittyPlus 1 2 3))`: types.GoType{12},
+		"(: Plus)":       types.GoType{0},
+		"(: Plus 1 2 3)": types.GoType{6},
+		`(: Plus 1 2 3
+			(: Plus 1 2 3))`: types.GoType{12},
 	}
 
 	for input, output := range m {