diff --git a/src/sb2/mod.rs b/src/sb2/mod.rs
index 5a42e26..0355cfe 100644
--- a/src/sb2/mod.rs
+++ b/src/sb2/mod.rs
@@ -213,61 +213,239 @@ pub struct Info {
 pub struct TopLevelScript {
     pub x: f64,
     pub y: f64,
-    pub script: Script,
+    pub script: Vec<Block>,
 }
 
-type Script = Vec<Block>;
+#[derive(Debug)]
+#[derive(Deserialize, Serialize)]
+#[serde(untagged)]
+pub enum Block {
+    DefineProcedure(DefineProcedure),
+    EBlock(EBlock),
+    CBlock(CBlock),
+    BasicBlock(BasicBlock),
+}
 
 #[derive(Debug)]
-pub struct Block {
+pub struct BasicBlock {
     pub opcode: String,
     pub args: Vec<BlockArgument>,
 }
-type BlockArgument = serde_json::Value;
 
-/*
+#[derive(Debug)]
+pub struct CBlock {
+    pub opcode: String,
+    pub args: Vec<BlockArgument>,
+    pub branch: Vec<Block>,
+}
+
+#[derive(Debug)]
+pub struct EBlock {
+    pub opcode: String,
+    pub args: Vec<BlockArgument>,
+    pub branch0: Vec<Block>,
+    pub branch1: Vec<Block>,
+}
+
+#[derive(Debug)]
+#[derive(Deserialize, Serialize)]
+pub struct DefineProcedure {
+    pub opcode: String, // always "procDef"
+    pub spec: String,
+    pub parameter_names: Vec<String>,
+    pub default_arg_values: Vec<LiteralValue>,
+    pub run_without_screen_refresh: bool,
+}
+
 #[derive(Debug)]
 #[derive(Deserialize, Serialize)]
 #[serde(untagged)]
 pub enum BlockArgument {
-    Literal(serde_json::Value),
+    Boolean(bool),
+    Number(f64),
+    String(String),
+    Reporter(BasicBlock),
 }
-*/
 
-impl<'de> Deserialize<'de> for Block {
+#[derive(Debug)]
+#[derive(Deserialize, Serialize)]
+#[serde(untagged)]
+pub enum LiteralValue {
+    Boolean(bool),
+    Number(f64),
+    String(String),
+}
+
+impl From<&str> for BlockArgument {
+    fn from(value: &str) -> Self {
+        BlockArgument::String(value.to_string())
+    }
+}
+
+impl<'de> Deserialize<'de> for EBlock {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
         where D: serde::Deserializer<'de>,
     {
-        struct BlockVisitor;
+        struct EBlockVisitor;
 
-        impl<'de> Visitor<'de> for BlockVisitor {
-            type Value = Block;
+        impl<'de> Visitor<'de> for EBlockVisitor {
+            type Value = EBlock;
 
             fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
-                formatter.write_str("an array containing an opcode optionally followed by inputs")
+                formatter.write_str("a script block with two branches (an 'E block')")
             }
 
             fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
                 where A: serde::de::SeqAccess<'de>,
             {
-                let opcode = seq.next_element()?.ok_or_else(|| {
-                    de::Error::custom("could not read opcode for script block")
-            })?;
+                let opcode = seq.next_element()?.ok_or_else(||
+                    de::Error::custom("could not read opcode for E block")
+                )?;
 
-                let mut args = Vec::<BlockArgument>::with_capacity(seq.size_hint().unwrap_or(0));
-                while let Some(arg) = seq.next_element::<serde_json::Value>()? {
+                let mut args = vec![];
+                let mut branches: [serde_json::Value; 2] = [
+                    seq.next_element()?.ok_or_else(||
+                        de::Error::custom("could not find first branch for E block")
+                    )?,
+                    seq.next_element()?.ok_or_else(||
+                        de::Error::custom("could not find second branch for E block")
+                    )?,
+                ];
+                while let Some(next_element) = seq.next_element::<serde_json::Value>()? {
+                    let arg = serde_json::from_value::<BlockArgument>(branches[0].take()).map_err(|_|
+                        de::Error::custom("could not interpret argument for E block")
+                    )?;
                     args.push(arg);
+                    branches[0] = branches[1].take();
+                    branches[1] = next_element;
                 }
-
-                Ok(Block { opcode, args })
+                Ok(EBlock {
+                    opcode,
+                    args,
+                    branch0: serde_json::from_value(branches[0].take()).map_err(|_|
+                        de::Error::custom("could not interpret first branch for E block")
+                    )?,
+                    branch1: serde_json::from_value(branches[1].take()).map_err(|_|
+                        de::Error::custom("could not interpret second branch for E block")
+                    )?,
+                })
             }
         }
 
-        deserializer.deserialize_seq(BlockVisitor)
+        deserializer.deserialize_seq(EBlockVisitor)
     }
 }
 
-impl Serialize for Block {
+impl Serialize for EBlock {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where S: serde::Serializer
+    {
+        let mut state = serializer.serialize_seq(Some(3 + self.args.len()))?;
+        state.serialize_element(&self.opcode)?;
+        for arg in &self.args {
+            state.serialize_element(arg)?;
+        }
+        state.serialize_element(&self.branch0)?;
+        state.serialize_element(&self.branch1)?;
+        state.end()
+    }
+}
+
+impl<'de> Deserialize<'de> for CBlock {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where D: serde::Deserializer<'de>,
+    {
+        struct CBlockVisitor;
+
+        impl<'de> Visitor<'de> for CBlockVisitor {
+            type Value = CBlock;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+                formatter.write_str("a script block with one branch (a 'C block')")
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+                where A: serde::de::SeqAccess<'de>,
+            {
+                let opcode = seq.next_element()?.ok_or_else(||
+                    de::Error::custom("could not read opcode for C block")
+                )?;
+
+                let mut args = vec![];
+                let mut branch = seq.next_element()?.ok_or_else(||
+                        de::Error::custom("could not find branch for C block")
+                    )?;
+                while let Some(next_element) = seq.next_element::<serde_json::Value>()? {
+                    let arg = serde_json::from_value::<BlockArgument>(branch).map_err(|_|
+                        de::Error::custom("could not interpret argument for C block")
+                    )?;
+                    args.push(arg);
+                    branch = next_element;
+                }
+                Ok(CBlock {
+                    opcode,
+                    args,
+                    branch: serde_json::from_value(branch).map_err(|_|
+                        de::Error::custom("could not interpret first branch for C block")
+                    )?,
+                })
+            }
+        }
+
+        deserializer.deserialize_seq(CBlockVisitor)
+    }
+}
+
+impl Serialize for CBlock {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where S: serde::Serializer
+    {
+        let mut state = serializer.serialize_seq(Some(2 + self.args.len()))?;
+        state.serialize_element(&self.opcode)?;
+        for arg in &self.args {
+            state.serialize_element(arg)?;
+        }
+        state.serialize_element(&self.branch)?;
+        state.end()
+    }
+}
+
+impl<'de> Deserialize<'de> for BasicBlock {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where D: serde::Deserializer<'de>,
+    {
+        struct BasicBlockVisitor;
+
+        impl<'de> Visitor<'de> for BasicBlockVisitor {
+            type Value = BasicBlock;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+                formatter.write_str("a script block with no branches")
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+                where A: serde::de::SeqAccess<'de>,
+            {
+                let opcode = seq.next_element()?.ok_or_else(||
+                    de::Error::custom("could not read opcode for block")
+                )?;
+
+                let mut args = vec![];
+                while let Some(next_argument) = seq.next_element()? {
+                    args.push(next_argument);
+                }
+                Ok(BasicBlock {
+                    opcode,
+                    args,
+                })
+            }
+        }
+
+        deserializer.deserialize_seq(BasicBlockVisitor)
+    }
+}
+
+impl Serialize for BasicBlock {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
         where S: serde::Serializer
     {