Test function calls

spec/ast/function_call_spec.rb

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+RSpec.describe AST::FunctionCall do
+  it 'evaluates built-in functions' do
+    expect {
+      AST::FunctionCall.new(
+        AST::Identifier.new('print'),
+        [AST::String.new('hello world')]
+      ).execute(Environment.new)
+    }.to output("hello world\n").to_stdout
+  end
+
+  it 'evaluates user-defined functions' do
+    env = Environment.new
+    AST::FunctionDefinition.new(
+      AST::Identifier.new('add_one'),
+      [AST::Identifier.new('n')],
+      AST::Block.new([
+        AST::Binary.new(
+          AST::Operators::ADD,
+          AST::Identifier.new('n'),
+          AST::Number.new(1.0)
+        )
+      ])
+    ).execute(env)
+    expect(
+      AST::FunctionCall.new(
+        AST::Identifier.new('add_one'),
+        [AST::Number.new(5.0)]
+      ).execute(env)
+    ).to eq(6.0)
+  end
+
+  # This corresponds to the program
+  # function factorial(n) {
+  #   if n == 0 {
+  #     1;
+  #   } else {
+  #     n * factorial(n - 1);
+  #   }
+  # }
+  # factorial(5);
+  it 'evaluates recursive functions' do
+    env = Environment.new
+    AST::FunctionDefinition.new(
+      AST::Identifier.new('factorial'),
+      [AST::Identifier.new('n')],
+      AST::Block.new([
+        AST::Conditional.new(
+          [
+            AST::Branch.new(
+              AST::Binary.new(
+                AST::Operators::DOUBLE_EQUALS,
+                AST::Identifier.new('n'),
+                AST::Number.new(0.0),
+              ),
+              AST::Block.new([
+                AST::Number.new(1.0),
+              ])
+            ),
+            AST::Branch.new(
+              AST::Boolean.new(true),
+              AST::Block.new([
+                AST::Binary.new(
+                  AST::Operators::MULTIPLY,
+                  AST::Identifier.new('n'),
+                  AST::FunctionCall.new(
+                    AST::Identifier.new('factorial'),
+                    [
+                      AST::Binary.new(
+                        AST::Operators::SUBTRACT,
+                        AST::Identifier.new('n'),
+                        AST::Number.new(1.0),
+                      )
+                    ]
+                  )
+                )
+              ])
+            ),
+          ]
+        )
+      ])
+    ).execute(env)
+    expect(
+      AST::FunctionCall.new(
+        AST::Identifier.new('factorial'),
+        [AST::Number.new(5.0)]
+      ).execute(env)
+    ).to eq(120.0)
+  end
+end