diff --git a/Cargo.lock b/Cargo.lock
index b70139f7..a3ec426c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -149,6 +149,8 @@ dependencies = [
  "clap",
  "combine",
  "hex",
+ "strum",
+ "strum_macros",
 ]
 
 [[package]]
@@ -199,12 +201,37 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "rustversion"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f2cc38e8fa666e2de3c4aba7edeb5ffc5246c1c2ed0e3d17e560aeeba736b23f"
+
 [[package]]
 name = "strsim"
 version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
 
+[[package]]
+name = "strum"
+version = "0.24.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e96acfc1b70604b8b2f1ffa4c57e59176c7dbb05d556c71ecd2f5498a1dee7f8"
+
+[[package]]
+name = "strum_macros"
+version = "0.24.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6878079b17446e4d3eba6192bb0a2950d5b14f0ed8424b852310e5a94345d0ef"
+dependencies = [
+ "heck",
+ "proc-macro2",
+ "quote",
+ "rustversion",
+ "syn",
+]
+
 [[package]]
 name = "syn"
 version = "1.0.92"
diff --git a/Cargo.toml b/Cargo.toml
index 3118c9ee..b951c6c2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,3 +10,5 @@ anyhow = "1.0.57"
 clap = { version = "3.1.14", features = ["derive"] }
 combine = "4.6.4"
 hex = "0.4.3"
+strum = "0.24.0"
+strum_macros = "0.24.0"
diff --git a/src/ast.rs b/src/ast.rs
index 707b9b7b..258922e1 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -1,3 +1,5 @@
+use strum_macros::EnumString;
+
 #[derive(Debug)]
 pub struct Program {
     pub version: String,
@@ -27,7 +29,7 @@ pub enum Term {
     // tag: 6
     Error(Box<Term>),
     // tag: 7
-    // Builtin
+    Builtin(DefaultFunction),
 }
 
 #[derive(Debug, Clone)]
@@ -46,3 +48,78 @@ pub enum Constant {
     // tag: 5
     Bool(bool),
 }
+
+#[derive(Debug, Clone, EnumString)]
+pub enum DefaultFunction {
+    // Integer functions
+    AddInteger,
+    SubtractInteger,
+    MultiplyInteger,
+    DivideInteger,
+    QuotientInteger,
+    RemainderInteger,
+    ModInteger,
+    EqualsInteger,
+    LessThanInteger,
+    LessThanEqualsInteger,
+    // ByteString functions
+    AppendByteString,
+    ConsByteString,
+    SliceByteString,
+    LengthOfByteString,
+    IndexByteString,
+    EqualsByteString,
+    LessThanByteString,
+    LessThanEqualsByteString,
+    // Cryptography and hash functions
+    Sha2_256,
+    Sha3_256,
+    Blake2b_256,
+    VerifySignature,
+    VerifyEcdsaSecp256k1Signature,
+    VerifySchnorrSecp256k1Signature,
+    // String functions
+    AppendString,
+    EqualsString,
+    EncodeUtf8,
+    DecodeUtf8,
+    // Bool function
+    IfThenElse,
+    // Unit function
+    ChooseUnit,
+    // Tracing function
+    Trace,
+    // Pairs functions
+    FstPair,
+    SndPair,
+    // List functions
+    ChooseList,
+    MkCons,
+    HeadList,
+    TailList,
+    NullList,
+    // Data functions
+    // It is convenient to have a "choosing" function for a data type that has more than two
+    // constructors to get pattern matching over it and we may end up having multiple such data
+    // types, hence we include the name of the data type as a suffix.
+    ChooseData,
+    ConstrData,
+    MapData,
+    ListData,
+    IData,
+    BData,
+    UnConstrData,
+    UnMapData,
+    UnListData,
+    UnIData,
+    UnBData,
+    EqualsData,
+    SerialiseData,
+    // Misc constructors
+    // Constructors that we need for constructing e.g. Data. Polymorphic builtin
+    // constructors are often problematic (See note [Representable built-in
+    // functions over polymorphic built-in types])
+    MkPairData,
+    MkNilData,
+    MkNilPairData,
+}
diff --git a/src/parser.rs b/src/parser.rs
index 5c09f10d..fe4096f5 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -1,3 +1,5 @@
+use std::str::FromStr;
+
 use combine::{
     attempt, between, choice, many1,
     parser::char::{alpha_num, digit, hex_digit, space, spaces, string},
@@ -6,7 +8,7 @@ use combine::{
     token, EasyParser, ParseError, Parser, Stream,
 };
 
-use crate::ast::{Constant, Program, Term};
+use crate::ast::{Constant, DefaultFunction, Program, Term};
 
 pub fn program(src: &str) -> anyhow::Result<Program> {
     let mut parser = program_();
@@ -136,7 +138,31 @@ where
     )
 }
 
-fn constant<Input>() -> impl Parser<Input, Output = Term>
+pub fn builtin<Input>() -> impl Parser<Input, Output = Term>
+where
+    Input: Stream<Token = char>,
+    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
+{
+    string("builtin")
+        .with(skip_many1(space()))
+        .with(many1(alpha_num()))
+        .map(|builtin_name: String| {
+            Term::Builtin(DefaultFunction::from_str(&builtin_name).unwrap())
+        })
+}
+
+pub fn error<Input>() -> impl Parser<Input, Output = Term>
+where
+    Input: Stream<Token = char>,
+    Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,
+{
+    string("error")
+        .with(skip_many1(space()))
+        .with(term_())
+        .map(|term| Term::Error(Box::new(term)))
+}
+
+pub fn constant<Input>() -> impl Parser<Input, Output = Term>
 where
     Input: Stream<Token = char>,
     Input::Error: ParseError<Input::Token, Input::Range, Input::Position>,