Incorrect format for negative numbers in the Alloy generator

[JLiangWaterloo]

Translate the following model

abstract Y
    y:int

Z : Y
    [y = -1]

The output

open util/integer
pred show {}
run  show for 1

abstract sig c1_Y
{ r_c2_y : one c2_y }
sig c2_y
{ ref : one Int }
{ one @r_c2_y.this }
one sig c3_Z extends c1_Y
{}
{ (this.@r_c2_y.@ref) = (1-) }

The last line shoud be -1 instead of the syntactically incorrect 1-