Merge pull request #28 from ancorso/depth_lim_iss

Fixes an error related to depth-limit in grammars without terminal rules

src/ExprRules.jl

@@ -432,9 +432,13 @@ Generates a random RuleNode of return type typ and maximum depth max_depth.
 function Base.rand(::Type{RuleNode}, grammar::Grammar, typ::Symbol, max_depth::Int=10, 
     bin::Union{NodeRecycler,Nothing}=nothing)
     rules = grammar[typ]
-    rule_index = max_depth > 1 ?
-        StatsBase.sample(rules) :
-        StatsBase.sample(filter(r->isterminal(grammar,r), rules))
+
+    if max_depth <= 1
+        terminals = filter(r->isterminal(grammar,r), rules)
+        rule_index = !isempty(terminals) ? StatsBase.sample(terminals) : StatsBase.sample(rules)
+    else    
+        rule_index = StatsBase.sample(rules)
+    end
 
     rulenode = iseval(grammar, rule_index) ?
         RuleNode(bin, rule_index, Core.eval(grammar, rule_index)) :

test/runtests.jl

@@ -428,6 +428,17 @@ let
     interpret(tab, ex) == exp.([1, 2])
 end
 
+let
+    grammar = @grammar begin
+        A = B
+        B = C
+        C = D
+        D = E
+        E = 1
+    end
+    rulenode = rand(RuleNode, grammar, :A, 1)
+end
+
 let
     S = SymbolTable(:x => [1,2,3], :y => [0,2,4], :b1 => [1,1,1], :b2=>[1,0,1])
     @test all(interpret(S, Meta.parse("x .<= y")) .== [false, true, true])