Better type promotion computation in _varmap_to_vars

Author: YingboMa

src/variables.jl

@@ -72,12 +72,21 @@ function _varmap_to_vars(varmap::Dict, varlist; defaults=Dict(), check=false, to
     varmap = merge(defaults, varmap) # prefers the `varmap`
     varmap = Dict(toterm(value(k))=>value(varmap[k]) for k in keys(varmap))
     # resolve symbolic parameter expressions
+    example_val = nothing
     for (p, v) in pairs(varmap)
-        varmap[p] = fixpoint_sub(v, varmap)
+        val = varmap[p] = fixpoint_sub(v, varmap)
+        if example_val === nothing && unwrap(val) isa Number
+            example_val = val
+        end
     end
     vs = values(varmap)
     T′ = eltype(vs)
-    T = Base.isconcretetype(T′) ? T′ : float(typeof(first(vs)))
+    if Base.isconcretetype(T′)
+        T = T′
+    else
+        example_val === nothing && throw_missingvars(varlist)
+        T = float(typeof(example_val))
+    end
     out = Vector{T}(undef, length(varlist))
     missingvars = setdiff(varlist, keys(varmap))
     check && (isempty(missingvars) || throw_missingvars(missingvars))