Implement option value

examples/option.ds

@@ -0,0 +1,6 @@
+create_user = (fn email <string>, name <option(string)>) <map> {
+	{
+		email = email
+		username = (either_or username email)
+	}
+}

src/abstract_tree/function_call.rs

@@ -28,6 +28,7 @@ impl AbstractTree for FunctionCall {
         let function_expression = Expression::from_syntax_node(source, expression_node, context)?;
         let function_type = function_expression.expected_type(context)?;
 
+        let mut minimum_parameter_count = 0;
         let mut arguments = Vec::new();
 
         for index in 2..node.child_count() - 1 {
@@ -43,6 +44,11 @@ impl AbstractTree for FunctionCall {
                 } = &function_type
                 {
                     if let Some(r#type) = parameter_types.get(argument_index) {
+                        if let Type::Option(_) = r#type {
+                        } else {
+                            minimum_parameter_count += 1;
+                        }
+
                         r#type
                             .check(&expression_type)
                             .map_err(|error| error.at_node(child, source))?;
@@ -54,13 +60,13 @@ impl AbstractTree for FunctionCall {
         }
 
         if let Type::Function {
-            parameter_types, ..
+            parameter_types: _, ..
         } = &function_type
         {
-            if arguments.len() != parameter_types.len() {
-                return Err(Error::ExpectedFunctionArgumentAmount {
+            if arguments.len() < minimum_parameter_count {
+                return Err(Error::ExpectedFunctionArgumentMinimum {
                     source: source[expression_node.byte_range()].to_string(),
-                    expected: parameter_types.len(),
+                    minumum_expected: minimum_parameter_count,
                     actual: arguments.len(),
                 });
             }

src/built_in_functions/commands.rs

@@ -41,14 +41,18 @@ impl BuiltInFunction for Sh {
     }
 
     fn run(&self, arguments: &[Value], _context: &Map) -> Result<Value> {
-        Error::expect_argument_amount(self, 1, arguments.len())?;
-
         let command_text = arguments.first().unwrap().as_string()?;
         let mut command = Command::new("sh");
 
         command.arg("-c");
         command.arg(command_text);
 
+        let extra_command_text = arguments.get(1).unwrap_or_default().as_option()?;
+
+        if let Some(text) = extra_command_text {
+            command.args(["--", text.as_string()?]);
+        }
+
         let output = command.spawn()?.wait_with_output()?.stdout;
 
         Ok(Value::String(String::from_utf8(output)?))
@@ -56,7 +60,7 @@ impl BuiltInFunction for Sh {
 
     fn r#type(&self) -> crate::Type {
         Type::Function {
-            parameter_types: vec![Type::String],
+            parameter_types: vec![Type::String, Type::Option(Box::new(Type::String))],
             return_type: Box::new(Type::String),
         }
     }

src/error.rs

@@ -74,9 +74,9 @@ pub enum Error {
     },
 
     /// A function was called with the wrong amount of arguments.
-    ExpectedArgumentMinimum {
-        function_name: &'static str,
-        minimum: usize,
+    ExpectedFunctionArgumentMinimum {
+        source: String,
+        minumum_expected: usize,
         actual: usize,
     },
 
@@ -136,6 +136,10 @@ pub enum Error {
         actual: Value,
     },
 
+    ExpectedOption {
+        actual: Value,
+    },
+
     /// A string, list, map or table value was expected.
     ExpectedCollection {
         actual: Value,
@@ -205,22 +209,6 @@ impl Error {
         }
     }
 
-    pub fn expect_argument_minimum<F: BuiltInFunction>(
-        function: &F,
-        minimum: usize,
-        actual: usize,
-    ) -> Result<()> {
-        if actual < minimum {
-            Ok(())
-        } else {
-            Err(Error::ExpectedArgumentMinimum {
-                function_name: function.name(),
-                minimum,
-                actual,
-            })
-        }
-    }
-
     pub fn is_type_check_error(&self, other: &Error) -> bool {
         match self {
             Error::WithContext { error, .. } => {
@@ -335,14 +323,16 @@ impl fmt::Display for Error {
                 f,
                 "{source} expected {expected} arguments, but got {actual}.",
             ),
-            ExpectedArgumentMinimum {
-                function_name,
-                minimum,
+            ExpectedFunctionArgumentMinimum {
+                source,
+                minumum_expected,
                 actual,
-            } => write!(
-                f,
-                "{function_name} expected a minimum of {minimum} arguments, but got {actual}.",
-            ),
+            } => {
+                write!(
+                    f,
+                    "{source} expected at least {minumum_expected} arguments, but got {actual}."
+                )
+            }
             ExpectedString { actual } => {
                 write!(f, "Expected a string but got {actual}.")
             }
@@ -379,6 +369,7 @@ impl fmt::Display for Error {
             ExpectedFunction { actual } => {
                 write!(f, "Expected function, but got {actual}.")
             }
+            ExpectedOption { actual } => write!(f, "Expected option, but got {actual}."),
             ExpectedCollection { actual } => {
                 write!(
                     f,

src/value/function.rs

@@ -2,7 +2,7 @@ use std::fmt::{self, Display, Formatter};
 
 use serde::{Deserialize, Serialize};
 
-use crate::{AbstractTree, Block, Error, Identifier, Map, Result, Type, Value};
+use crate::{AbstractTree, Block, Identifier, Map, Result, Type, Value};
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Function {
@@ -48,14 +48,6 @@ impl Function {
     }
 
     pub fn call(&self, arguments: &[Value], source: &str, outer_context: &Map) -> Result<Value> {
-        if self.parameters.len() != arguments.len() {
-            return Err(Error::ExpectedFunctionArgumentAmount {
-                source: "unknown".to_string(),
-                expected: self.parameters.len(),
-                actual: arguments.len(),
-            });
-        }
-
         let context = Map::clone_from(outer_context)?;
         let parameter_argument_pairs = self.parameters.iter().zip(arguments.iter());
 

src/value/mod.rs

@@ -220,6 +220,16 @@ impl Value {
         }
     }
 
+    /// Returns `Option`, or returns `Err` if `self` is not a `Value::Option`.
+    pub fn as_option(&self) -> Result<&Option<Box<Value>>> {
+        match self {
+            Value::Option(option) => Ok(option),
+            value => Err(Error::ExpectedOption {
+                actual: value.clone(),
+            }),
+        }
+    }
+
     /// Returns `()`, or returns `Err` if `self` is not a `Value::Option(None)`.
     pub fn as_none(&self) -> Result<()> {
         match self {