Write docs

src/built_in_functions/mod.rs

@@ -7,7 +7,7 @@ use std::fmt::{self, Display, Formatter};
 use rand::{random, thread_rng, Rng};
 use serde::{Deserialize, Serialize};
 
-use crate::{error::RuntimeError, Context, Format, Type, Value};
+use crate::{error::RuntimeError, Context, EnumInstance, Format, Identifier, Type, Value};
 
 use self::{fs::Fs, json::Json, str::StrFunction};
 
@@ -70,7 +70,10 @@ impl Callable for BuiltInFunction {
 
     fn r#type(&self) -> Type {
         match self {
-            BuiltInFunction::AssertEqual => Type::function(vec![Type::Any, Type::Any], Type::None),
+            BuiltInFunction::AssertEqual => Type::function(
+                vec![Type::Any, Type::Any],
+                Type::Custom(Identifier::new("Result")),
+            ),
             BuiltInFunction::Fs(fs_function) => fs_function.r#type(),
             BuiltInFunction::Json(json_function) => json_function.r#type(),
             BuiltInFunction::Length => Type::function(vec![Type::Collection], Type::Integer),
@@ -93,10 +96,24 @@ impl Callable for BuiltInFunction {
             BuiltInFunction::AssertEqual => {
                 RuntimeError::expect_argument_amount(self.name(), 2, arguments.len())?;
 
-                let left = arguments.first().unwrap();
+                let left = arguments.get(0).unwrap();
                 let right = arguments.get(1).unwrap();
 
-                Ok(Value::Boolean(left == right))
+                let result = if left == right {
+                    Value::Enum(EnumInstance::new(
+                        "Result".to_string(),
+                        "Ok".to_string(),
+                        Value::none(),
+                    ))
+                } else {
+                    Value::Enum(EnumInstance::new(
+                        "Result".to_string(),
+                        "Error".to_string(),
+                        Value::none(),
+                    ))
+                };
+
+                Ok(result)
             }
             BuiltInFunction::Fs(fs_function) => {
                 fs_function.call(arguments, _source, _outer_context)

src/context.rs

@@ -1,3 +1,32 @@
+//! An execution context that store variables and type data during the
+//! [Interpreter][crate::Interpreter]'s abstraction and execution process.
+//!
+//! ## Setting values
+//!
+//! When data is stored in a context, it can be accessed by dust source code.
+//! This allows you to insert values and type definitions before any code is
+//! interpreted.
+//!
+//! ```
+//! # use dust_lang::*;
+//! let context = Context::new();
+//!
+//! context.set_value(
+//!     "foobar".to_string(),
+//!     Value::String("FOOBAR".to_string())
+//! ).unwrap();
+//!
+//! interpret_with_context("output foobar", context);
+//!
+//! // Stdout: "FOOBAR"
+//! ```
+//!
+//! ## Built-in values and type definitions
+//!
+//! When looking up values and definitions, the Context will try to use one that
+//! has been explicitly set. If nothing is found, it will then check the built-
+//! in values and type definitions for a match. This means that the user can
+//! override the built-ins.
 use std::{
     cmp::Ordering,
     collections::BTreeMap,
@@ -9,22 +38,29 @@ use crate::{
     error::rw_lock_error::RwLockError, Type, TypeDefinition, Value,
 };
 
+/// An execution context that variable and type data during the [Interpreter]'s
+/// abstraction and execution process.
+///
+/// See the [module-level docs][self] for more info.
 #[derive(Clone, Debug)]
 pub struct Context {
     inner: Arc<RwLock<BTreeMap<String, ValueData>>>,
 }
 
 impl Context {
+    /// Return a new, empty Context.
     pub fn new() -> Self {
         Self {
             inner: Arc::new(RwLock::new(BTreeMap::new())),
         }
     }
 
+    /// Return a lock guard to the inner BTreeMap.
     pub fn inner(&self) -> Result<RwLockReadGuard<BTreeMap<String, ValueData>>, RwLockError> {
         Ok(self.inner.read()?)
     }
 
+    /// Create a new context with all of the data from an existing context.
     pub fn with_variables_from(other: &Context) -> Result<Context, RwLockError> {
         let mut new_variables = BTreeMap::new();
 
@@ -37,6 +73,25 @@ impl Context {
         })
     }
 
+    /// Modify a context to take on all of the key-value pairs of another.
+    ///
+    /// In the case of the conflict, the inherited value will override the previous
+    /// value.
+    ///
+    /// ```
+    /// # use dust_lang::*;
+    /// let first_context = Context::new();
+    /// let second_context = Context::new();
+    ///
+    /// second_context.set_value(
+    /// "Foo".to_string(),
+    /// Value::String("Bar".to_string())
+    /// );
+    ///
+    /// first_context.inherit_from(&second_context).unwrap();
+    ///
+    /// assert_eq!(first_context, second_context);
+    /// ```
     pub fn inherit_from(&self, other: &Context) -> Result<(), RwLockError> {
         let mut self_variables = self.inner.write()?;
 
@@ -53,6 +108,10 @@ impl Context {
         Ok(())
     }
 
+    /// Get a value from the context.
+    ///
+    /// This will also return a built-in value if one matches the key. See the
+    /// [module-level docs][self] for more info.
     pub fn get_value(&self, key: &str) -> Result<Option<Value>, RwLockError> {
         if let Some(value_data) = self.inner.read()?.get(key) {
             if let ValueData::Value { inner, .. } = value_data {
@@ -69,18 +128,32 @@ impl Context {
         Ok(None)
     }
 
+    /// Get a type from the context.
+    ///
+    /// If the key matches a stored value, its type will be returned. It if
+    /// matches a type hint, the type hint will be returned.
     pub fn get_type(&self, key: &str) -> Result<Option<Type>, RwLockError> {
         if let Some(value_data) = self.inner.read()?.get(key) {
             match value_data {
-                ValueData::Value { inner, .. } => Ok(Some(inner.r#type())),
+                ValueData::Value { inner, .. } => return Ok(Some(inner.r#type())),
-                ValueData::ExpectedType { inner, .. } => Ok(Some(inner.clone())),
+                ValueData::TypeHint { inner, .. } => return Ok(Some(inner.clone())),
                 ValueData::TypeDefinition(_) => todo!(),
             }
-        } else {
-            Ok(None)
         }
+
+        for built_in_value in all_built_in_values() {
+            if key == built_in_value.name() {
+                return Ok(Some(built_in_value.r#type()));
+            }
+        }
+
+        Ok(None)
     }
 
+    /// Get a value from the context.
+    ///
+    /// This will also return a built-in type definition if one matches the key.
+    /// See the [module-level docs][self] for more info.
     pub fn get_definition(&self, key: &str) -> Result<Option<TypeDefinition>, RwLockError> {
         if let Some(value_data) = self.inner.read()?.get(key) {
             if let ValueData::TypeDefinition(definition) = value_data {
@@ -97,6 +170,7 @@ impl Context {
         Ok(None)
     }
 
+    /// Set a value to a key.
     pub fn set_value(&self, key: String, value: Value) -> Result<(), RwLockError> {
         self.inner.write()?.insert(
             key,
@@ -109,14 +183,22 @@ impl Context {
         Ok(())
     }
 
+    /// Set a type hint.
+    ///
+    /// This allows the interpreter to check a value's type before the value
+    /// actually exists by predicting what the abstract tree will produce.
     pub fn set_type(&self, key: String, r#type: Type) -> Result<(), RwLockError> {
         self.inner
             .write()?
-            .insert(key, ValueData::ExpectedType { inner: r#type });
+            .insert(key, ValueData::TypeHint { inner: r#type });
 
         Ok(())
     }
 
+    /// Set a type definition.
+    ///
+    /// This allows defined types (i.e. structs and enums) to be instantiated
+    /// later while using this context.
     pub fn set_definition(
         &self,
         key: String,
@@ -129,6 +211,7 @@ impl Context {
         Ok(())
     }
 
+    /// Remove a key-value pair.
     pub fn unset(&self, key: &str) -> Result<(), RwLockError> {
         self.inner.write()?.remove(key);
 
@@ -186,7 +269,7 @@ pub enum ValueData {
         inner: Value,
         runtime_uses: Arc<RwLock<u16>>,
     },
-    ExpectedType {
+    TypeHint {
         inner: Type,
     },
     TypeDefinition(TypeDefinition),
@@ -214,8 +297,8 @@ impl PartialEq for ValueData {
                 }
             }
             (
-                ValueData::ExpectedType { inner: left_inner },
+                ValueData::TypeHint { inner: left_inner },
-                ValueData::ExpectedType { inner: right_inner },
+                ValueData::TypeHint { inner: right_inner },
             ) => left_inner == right_inner,
             _ => false,
         }
@@ -243,12 +326,12 @@ impl Ord for ValueData {
             ) => inner_left.cmp(inner_right),
             (ValueData::Value { .. }, _) => Greater,
             (
-                ValueData::ExpectedType { inner: inner_left },
+                ValueData::TypeHint { inner: inner_left },
-                ValueData::ExpectedType { inner: inner_right },
+                ValueData::TypeHint { inner: inner_right },
             ) => inner_left.cmp(inner_right),
             (ValueData::TypeDefinition(left), ValueData::TypeDefinition(right)) => left.cmp(right),
             (ValueData::TypeDefinition(_), _) => Greater,
-            (ValueData::ExpectedType { .. }, _) => Less,
+            (ValueData::TypeHint { .. }, _) => Less,
         }
     }
 }

src/main.rs

@@ -311,7 +311,7 @@ impl Completer for DustCompleter {
         for (key, value_data) in self.context.inner().unwrap().iter() {
             let value = match value_data {
                 ValueData::Value { inner, .. } => inner,
-                ValueData::ExpectedType { .. } => continue,
+                ValueData::TypeHint { .. } => continue,
                 ValueData::TypeDefinition(_) => continue,
             };
 

tests/built_in_values.rs

@@ -4,3 +4,29 @@ use dust_lang::*;
 fn args() {
     assert!(interpret("args").is_ok_and(|value| value.is_list()));
 }
+
+#[test]
+fn assert_equal() {
+    assert_eq!(
+        interpret("assert_equal"),
+        Ok(Value::Function(Function::BuiltIn(
+            BuiltInFunction::AssertEqual
+        )))
+    );
+    assert_eq!(
+        interpret("assert_equal(false, false)"),
+        Ok(Value::Enum(EnumInstance::new(
+            "Result".to_string(),
+            "Ok".to_string(),
+            Value::none()
+        )))
+    );
+    assert_eq!(
+        interpret("assert_equal(true, false)"),
+        Ok(Value::Enum(EnumInstance::new(
+            "Result".to_string(),
+            "Error".to_string(),
+            Value::none()
+        )))
+    );
+}