Fix unary +, -, * (#72)

Author: odow

src/write.jl

@@ -447,7 +447,16 @@ function _write_expression(
     if f.head == :ifelse
         _write_ifelse(io, predicates, variables, f.args)
         return
-    elseif haskey(_INFIX_OPS, f.head)
+    elseif f.head in (:+, :*) && length(f.args) == 1
+        _write_expression(io, predicates, variables, f.args[1])
+        return
+    elseif f.head == :- && length(f.args) == 1
+        print(io, "-(")
+        _write_expression(io, predicates, variables, f.args[1])
+        print(io, ")")
+        return
+    end
+    if haskey(_INFIX_OPS, f.head)
         op = _INFIX_OPS[f.head]
         @assert length(f.args) > 1
         sep = string(" ", op, " ")

test/runtests.jl

@@ -1602,6 +1602,34 @@ function test_highs_int_frac_ub()
     return
 end
 
+function test_infix_unary_minus()
+    model = MOI.Utilities.Model{Float64}()
+    x, _ = MOI.add_constrained_variable(model, MOI.Interval(1.0, 3.0))
+    solver = MiniZinc.Optimizer{Float64}("highs")
+    f = MOI.ScalarNonlinearFunction(:-, Any[x])
+    MOI.set(model, MOI.ObjectiveSense(), MOI.MAX_SENSE)
+    MOI.set(model, MOI.ObjectiveFunction{typeof(f)}(), f)
+    index_map, _ = MOI.optimize!(solver, model)
+    @test MOI.get(solver, MOI.VariablePrimal(), index_map[x]) ≈ 1.0
+    @test MOI.get(solver, MOI.ObjectiveValue()) ≈ -1.0
+    return
+end
+
+function test_infix_unary_addition()
+    for op in (:+, :*)
+        model = MOI.Utilities.Model{Float64}()
+        x, _ = MOI.add_constrained_variable(model, MOI.Interval(1.0, 3.0))
+        solver = MiniZinc.Optimizer{Float64}("highs")
+        f = MOI.ScalarNonlinearFunction(op, Any[x])
+        MOI.set(model, MOI.ObjectiveSense(), MOI.MAX_SENSE)
+        MOI.set(model, MOI.ObjectiveFunction{typeof(f)}(), f)
+        index_map, _ = MOI.optimize!(solver, model)
+        @test MOI.get(solver, MOI.VariablePrimal(), index_map[x]) ≈ 3.0
+        @test MOI.get(solver, MOI.ObjectiveValue()) ≈ 3.0
+    end
+    return
+end
+
 end
 
 TestMiniZinc.runtests()