String indexing: panic

[vmarkovtsev]

The following code:

str := "123"
str[0] == '1'

panics with

ng eval panic: reflect: call of reflect.Value.SetInt on uint8 Value
goroutine 1 [running]:
runtime/debug.Stack(0x44, 0x0, 0x0)
	/usr/lib/go-1.9/src/runtime/debug/stack.go:24 +0xa7
runtime/debug.PrintStack()
	/usr/lib/go-1.9/src/runtime/debug/stack.go:16 +0x22
neugram.io/ng/eval.(*Program).Eval.func1(0xc42013a100, 0xc42011f610, 0xc42011f5f8)
	/home/vadim/Projects/go_unix/src/neugram.io/ng/eval/eval.go:476 +0x204
panic(0xbb0f60, 0xc4201985e0)
	/usr/lib/go-1.9/src/runtime/panic.go:491 +0x283
reflect.Value.SetInt(0xb8dc20, 0xc42010462c, 0x188, 0x31)
	/usr/lib/go-1.9/src/reflect/value.go:1429 +0x135
neugram.io/ng/eval.convert(0xbcf2a0, 0xc420104628, 0x99, 0x1163e40, 0xb8dc20, 0xc420104571, 0x88, 0xc4200ff140)
	/home/vadim/Projects/go_unix/src/neugram.io/ng/eval/eval.go:1347 +0x143e
neugram.io/ng/eval.(*Program).evalExpr(0xc42013a100, 0x1159c00, 0xc4200ff5c0, 0x0, 0x0, 0x0)
	/home/vadim/Projects/go_unix/src/neugram.io/ng/eval/eval.go:1428 +0x11b3
neugram.io/ng/eval.(*Program).evalExpr(0xc42013a100, 0x1159c40, 0xc4200fb1c0, 0x0, 0x0, 0x0)
	/home/vadim/Projects/go_unix/src/neugram.io/ng/eval/eval.go:1449 +0x3079
neugram.io/ng/eval.(*Program).evalStmt(0xc42013a100, 0x115a640, 0xc4200ff5f0, 0x0, 0x0, 0x0)
	/home/vadim/Projects/go_unix/src/neugram.io/ng/eval/eval.go:885 +0x4655
neugram.io/ng/eval.(*Program).Eval(0xc42013a100, 0x115a640, 0xc4200ff5f0, 0xc4201540c0, 0x0, 0x0, 0x0, 0x11535c0, 0xc420100c60)
	/home/vadim/Projects/go_unix/src/neugram.io/ng/eval/eval.go:497 +0x38c
main.handleResult(0x1, 0xc420100c40, 0x1, 0x1, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
	/home/vadim/Projects/go_unix/src/neugram.io/ng/ng.go:393 +0x7ff
main.loop(0xc400000000)
	/home/vadim/Projects/go_unix/src/neugram.io/ng/ng.go:385 +0x611
main.main()
	/home/vadim/Projects/go_unix/src/neugram.io/ng/ng.go:147 +0x641
ng: ng eval panic: reflect: call of reflect.Value.SetInt on uint8 Value