Blocks and statements

docs/ROADMAP.md

@@ -1,6 +1,8 @@
 # implementation roadmap
 
 - [ ] parser
+  - [ ] uniform function call syntax
+  - [ ] lossless syntax trees (rowan + ungrammar)
 - [ ] typechecker
 - [ ] interpreter
 - [ ] code generator
@@ -11,4 +13,5 @@
   - [ ] product types
   - [ ] sum types
     - [ ] variant types
+- [ ] pattern matching
 - [ ] trait / interface system

example.mul

@@ -1,7 +1,9 @@
-main = () {
-	print(sum_equals(1, 2, 3) == true)
+main = () -> {
+  result = sum_equals(1, 2, 3);
+  print(result)
 }
 
-sum_equals = (x, y, sum) {
-	equals(add(x, y), sum)
-}
+sum_equals = (x, y, expected) -> {
+  sum = add(x, y);
+  equals(sum, expected)
+}

src/main.rs

@@ -1,11 +1,22 @@
 use std::io::{stdin, stdout, BufRead, Write};
 
-use mul::parser::ExpressionParser;
+use mul::parser::{ExpressionParser, StatementParser};
+
+macro_rules! parse {
+    ($parser:expr, $line:expr) => {
+        match $parser.parse($line.as_str()) {
+            Ok(parsed) => println!("{parsed:?}"),
+            Err(lalrpop_util::ParseError::UnrecognizedEOF { .. }) => break,
+            Err(e) => println!("Parse error: {e}"),
+        }
+    };
+}
 
 fn main() {
     let mut stdin = stdin().lock();
     let mut stdout = stdout().lock();
-    let parser = ExpressionParser::new();
+    let expression = ExpressionParser::new();
+    let statement = StatementParser::new();
     loop {
         let mut line = String::new();
         print!("> ");
@@ -13,10 +24,10 @@ fn main() {
         stdin
             .read_line(&mut line)
             .expect("Failed to read from stdin");
-        match parser.parse(line.as_str()) {
-            Ok(parsed) => println!("{parsed:?}"),
-            Err(lalrpop_util::ParseError::UnrecognizedEOF { .. }) => break,
-            Err(e) => println!("Parse error: {e}"),
+        if line.trim_end().ends_with(';') {
+            parse!(statement, line)
+        } else {
+            parse!(expression, line)
         }
     }
 }

src/parser.lalrpop

@@ -1,19 +1,31 @@
-use crate::syntax::{Expression, Name};
+use crate::syntax::{Expression, Name, Statement};
 
 grammar;
 
+pub Statement: Statement = {
+    <name:Name> "=" <body:Expression> ";" => Statement::Binding(name, body),
+    <body:Expression> ";" => Statement::Expression(body),
+};
+
 pub Expression: Expression = {
-    "(" <params:Comma<Name>> ")" "{" <body:Expression> "}" => Expression::Lambda(params, Box::new(body)),
-    <callee:Expression> "(" <args:Comma<Expression>> ")" => Expression::Call(Box::new(callee), args),
+    "(" <params:Comma<Name>> ")" "->" <body:Expression> => Expression::Lambda(params, Box::new(body)),
+    Atom => <>,
+};
+
+Atom: Expression = {
     Name => Expression::Variable(<>),
+    "{" <statements:Statement*> <result:Expression> "}" => Expression::Block(statements, Box::new(result)),
+    <callee:Atom> "(" <args:Comma<Expression>> ")" => Expression::Call(Box::new(callee), args),
     Integer => Expression::Integer(<>),
     Boolean => Expression::Boolean(<>),
 };
 
 // TODO: decide on identifier syntax
-Name: Name = r"[a-zA-Z_]+" => <>.to_string();
+Name: Name =
+    r"[a-zA-Z_]+" => <>.to_string();
 
-Integer: i64 = r"[0-9]+" => <>.parse::<i64>().unwrap();
+Integer: i64 =
+    r"[0-9]+" => <>.parse::<i64>().unwrap();
 
 Boolean: bool = {
     "true" => true,

src/syntax.rs

@@ -1,10 +1,57 @@
+use std::fmt::Display;
+
 pub type Name = String;
 
+#[derive(Debug)]
+pub enum Statement {
+    Binding(Name, Expression),
+    Expression(Expression),
+}
+
+impl Display for Statement {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Statement::Binding(name, body) => write!(f, "{name} = {body};"),
+            Statement::Expression(body) => write!(f, "{body};"),
+        }
+    }
+}
+
 #[derive(Debug)]
 pub enum Expression {
     Variable(Name),
+    Block(Vec<Statement>, Box<Expression>),
     Lambda(Vec<Name>, Box<Expression>),
     Call(Box<Expression>, Vec<Expression>),
     Boolean(bool),
     Integer(i64),
 }
+
+impl Display for Expression {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Expression::Variable(name) => write!(f, "{name}"),
+            Expression::Block(statements, result) => {
+                writeln!(f, "{{")?;
+                for statement in statements {
+                    writeln!(f, "\t{statement}")?;
+                }
+                writeln!(f, "\t{result}")?;
+                writeln!(f, "}}")
+            }
+            Expression::Lambda(params, body) => write!(f, "({}) -> {body}", params.join(", ")),
+            Expression::Call(callee, args) => {
+                write!(f, "{callee}(")?;
+                if let Some(arg) = args.first() {
+                    write!(f, "{arg}")?;
+                }
+                for arg in args.iter().skip(1) {
+                    write!(f, ", {arg}")?;
+                }
+                write!(f, ")")
+            }
+            Expression::Boolean(v) => write!(f, "{v}"),
+            Expression::Integer(v) => write!(f, "{v}"),
+        }
+    }
+}