I have some barplot

```
barplot(1:3, axes=FALSE)

```

to which I would like to add horizontal gridlines with labels using base R. 

I get the first part using

```
par(xpd = TRUE, mai=c(0.5,1,0.5,0.2))  # to extend lines to the left of plotting area
barplot(1:3, axes=FALSE)               # plotting area
grid(nx=0, ny=3, col="gray")           # horizontal grid lines
barplot(1:3, axes=FALSE, add=TRUE)     # get grid lines into background

```

but I fail to get the labels on the left end. That is, at the left end of the gridlines, I would like to have the Y-values, here 1 and 2.