Evaluate conditionals

lib/chervil/ast/conditional.rb

@@ -13,5 +13,13 @@ module Chervil::AST
     def ==(other)
       @predicate == other.predicate && @true_branch == other.true_branch && @false_branch == other.false_branch
     end
+
+    def evaluate(env)
+      if @predicate.evaluate(env) == false
+        @false_branch.evaluate(env)
+      else
+        @true_branch.evaluate(env)
+      end
+    end
   end
 end

spec/ast/conditional_spec.rb

@@ -0,0 +1,55 @@
+module Chervil
+  RSpec.describe AST::Conditional do
+    it 'returns the true branch given #t' do
+      expect(AST::Conditional.new(
+        AST::Boolean.new(true),
+        AST::Number.new(1.0),
+        AST::Number.new(0.0),
+      ).evaluate(Env.new)).to eq(
+        1.0
+      )
+    end
+
+    it 'returns the false branch given #f' do
+      expect(AST::Conditional.new(
+        AST::Boolean.new(false),
+        AST::Number.new(1.0),
+        AST::Number.new(0.0),
+      ).evaluate(Env.new)).to eq(
+        0.0
+      )
+    end
+
+    it 'evaluates complex predicates' do
+      expect(AST::Conditional.new(
+        AST::Application.new(
+          AST::Identifier.new(">"),
+          [
+            AST::Number.new(2.0),
+            AST::Number.new(1.0),
+          ]
+        ),
+        AST::Number.new(2.0),
+        AST::Number.new(1.0),
+      ).evaluate(Env.new)).to eq(
+        2.0
+      )
+    end
+
+    it 'evaluates complex branches' do
+      expect(AST::Conditional.new(
+        AST::Boolean.new(true),
+        AST::Application.new(
+          AST::Identifier.new("+"),
+          [
+            AST::Number.new(2.0),
+            AST::Number.new(1.0),
+          ]
+        ),
+        AST::Number.new(0.0)
+      ).evaluate(Env.new)).to eq(
+        3.0
+      )
+    end
+  end
+end