add macro to define a variable (#470)

Author: jverzani

src/common.jl

@@ -14,6 +14,7 @@ export fromroots,
        integrate,
        derivative,
        variable,
+       @variable,
        isintegral,
        ismonic
 
@@ -865,6 +866,26 @@ variable(::Type{P}, var::SymbolLike) where {P <: AbstractPolynomial} = variable(
 variable(p::AbstractPolynomial, var = indeterminate(p)) = variable(typeof(p), var)
 variable(var::SymbolLike = :x) = variable(Polynomial{Int}, var)
 
+#@variable x
+#@variable x::Polynomial
+#@variable x::Polynomial{t]
+macro variable(x)
+    q = Expr(:block)
+    if isa(x, Expr) && x.head == :(::)
+        x, P = x.args
+        push!(q.args, Expr(:(=), esc(x),
+                           Expr(:call, :variable, P, Expr(:quote, x))))
+    else
+        push!(q.args, Expr(:(=), esc(x),
+                           Expr(:call, :variable, Expr(:quote, x))))
+    end
+    push!(q.args, esc(x))
+
+    q
+end
+
+
+
 # basis
 # var is a positional argument, not a keyword; can't deprecate so we do `_var; var=_var`
 # return the kth basis polynomial for the given polynomial type, e.g. x^k for Polynomial{T}

test/StandardBasis.jl

@@ -63,6 +63,9 @@ isimmutable(::Type{<:ImmutablePolynomial}) = true
             ## issue #452
             ps = (1, 1.0)
             P != FactoredPolynomial && @test eltype(P(ps)) == eltype(promote(ps...))
+            ## issue 464
+            @variable z
+            @test z^2 + 2 == Polynomial([2,0,1], :z)
         end
     end
 end