From 318a842241fccef0184c69e31a7d08306799c6c6 Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Sat, 4 May 2024 13:45:43 +0200
Subject: rebel-parse, rebel-lang: implement if-else expressions

---
 crates/rebel-lang/src/typing.rs          | 28 ++++++++++++++++++++++++++++
 crates/rebel-lang/src/value.rs           | 21 +++++++++++++++++++++
 crates/rebel-parse/src/ast/expr.rs       | 17 +++++++++++++++++
 crates/rebel-parse/src/grammar/recipe.rs | 15 ++++++++++++---
 4 files changed, 78 insertions(+), 3 deletions(-)

diff --git a/crates/rebel-lang/src/typing.rs b/crates/rebel-lang/src/typing.rs
index 5a0ca0a..6c5ba81 100644
--- a/crates/rebel-lang/src/typing.rs
+++ b/crates/rebel-lang/src/typing.rs
@@ -200,6 +200,10 @@ impl<'scope> Context<'scope> {
 			Index { base, index } => self.type_index(base, index),
 			Field { base, field } => self.type_field(base, field),
 			Block(block) => self.type_block(block),
+			IfElse {
+				if_blocks,
+				else_block,
+			} => self.type_ifelse(if_blocks, else_block),
 			Paren(subexpr) => self.type_expr(subexpr),
 			Path(path) => self.type_path(path),
 			Literal(lit) => self.type_literal(lit),
@@ -379,6 +383,30 @@ impl<'scope> Context<'scope> {
 		Ok(ret)
 	}
 
+	fn type_ifelse(
+		&mut self,
+		if_blocks: &[(expr::Expr, ast::Block)],
+		else_block: &Option<Box<ast::Block>>,
+	) -> Result<Type> {
+		let (mut ret, mut common_upvalues) = if let Some(block) = else_block {
+			self.type_scope(&block.0)?
+		} else {
+			(Type::Unit, HashSet::new())
+		};
+
+		for (cond, block) in if_blocks {
+			Type::Bool.unify(self.type_expr(cond)?, Coerce::Assign)?;
+
+			let (typ, upvalues) = self.type_scope(&block.0)?;
+			ret = ret.unify(typ, Coerce::Common)?;
+			common_upvalues = &common_upvalues & &upvalues;
+		}
+
+		self.0.initialize_all(common_upvalues);
+
+		Ok(ret)
+	}
+
 	fn type_path(&self, path: &ast::Path<'_>) -> Result<Type> {
 		let var = self.0.lookup_value(path)?;
 		if !self.0.is_initialized(path) {
diff --git a/crates/rebel-lang/src/value.rs b/crates/rebel-lang/src/value.rs
index 2b07803..97a6f8b 100644
--- a/crates/rebel-lang/src/value.rs
+++ b/crates/rebel-lang/src/value.rs
@@ -107,6 +107,10 @@ impl<'scope> Context<'scope> {
 			Index { base, index } => self.eval_index(base, index),
 			Field { base, field } => self.eval_field(base, field),
 			Block(block) => self.eval_block(block),
+			IfElse {
+				if_blocks,
+				else_block,
+			} => self.eval_ifelse(if_blocks, else_block),
 			Paren(subexpr) => self.eval_expr(subexpr),
 			Path(path) => self.eval_path(path),
 			Literal(lit) => self.eval_literal(lit),
@@ -323,6 +327,23 @@ impl<'scope> Context<'scope> {
 		Ok(ret)
 	}
 
+	fn eval_ifelse(
+		&mut self,
+		if_blocks: &[(expr::Expr, ast::Block)],
+		else_block: &Option<Box<ast::Block>>,
+	) -> Result<Value> {
+		for (cond, block) in if_blocks {
+			if self.eval_expr(cond)? == Value::Bool(true) {
+				return self.eval_block(block);
+			}
+		}
+		if let Some(block) = else_block {
+			self.eval_block(block)
+		} else {
+			Ok(Value::Unit)
+		}
+	}
+
 	fn eval_path(&self, path: &ast::Path<'_>) -> Result<Value> {
 		Ok(self.0.lookup_value(path)?.clone())
 	}
diff --git a/crates/rebel-parse/src/ast/expr.rs b/crates/rebel-parse/src/ast/expr.rs
index 2e8d750..3994296 100644
--- a/crates/rebel-parse/src/ast/expr.rs
+++ b/crates/rebel-parse/src/ast/expr.rs
@@ -34,6 +34,10 @@ pub enum Expr<'a> {
 		field: Ident<'a>,
 	},
 	Block(Block<'a>),
+	IfElse {
+		if_blocks: Vec<(Expr<'a>, Block<'a>)>,
+		else_block: Option<Box<Block<'a>>>,
+	},
 	Paren(Box<Expr<'a>>),
 	Path(Path<'a>),
 	Literal(Literal<'a>),
@@ -129,6 +133,19 @@ impl<'a> Expr<'a> {
 				}
 				Ok(())
 			}
+			Expr::IfElse {
+				if_blocks,
+				else_block,
+			} => {
+				for (cond, block) in if_blocks {
+					cond.validate()?;
+					block.validate()?;
+				}
+				if let Some(block) = else_block {
+					block.validate()?;
+				}
+				Ok(())
+			}
 			Expr::Paren(expr) => expr.validate(),
 			Expr::Path(_) => Ok(()),
 			Expr::Literal(lit) => lit.validate(),
diff --git a/crates/rebel-parse/src/grammar/recipe.rs b/crates/rebel-parse/src/grammar/recipe.rs
index 11f1ce6..1ada80c 100644
--- a/crates/rebel-parse/src/grammar/recipe.rs
+++ b/crates/rebel-parse/src/grammar/recipe.rs
@@ -133,15 +133,24 @@ peg::parser! {
 			}
 			base:@ p('.') field:field() { Expr::field(base, field) }
 			--
-			p('(') e:expr() p(')') { Expr::paren(e) }
-			p('{') block:block() p('}') { Expr::Block(block) }
 			e:atom() { e }
 		}
 
 		rule atom() -> Expr<'a>
-			= lit:literal() { Expr::Literal(lit) }
+			= p('(') e:expr() p(')') { Expr::paren(e) }
+			/ [Token::Keyword(Keyword::If)]
+				if_blocks:(cond_block() ++ ([Token::Keyword(Keyword::Else)] [Token::Keyword(Keyword::If)]))
+				else_block:([Token::Keyword(Keyword::Else)] p('{') block:block() p('}') { Box::new(block) })?
+			{
+				Expr::IfElse { if_blocks, else_block }
+			}
+			/ p('{') block:block() p('}') { Expr::Block(block) }
+			/ lit:literal() { Expr::Literal(lit) }
 			/ path:path() { Expr::Path(path) }
 
+		rule cond_block() -> (Expr<'a>, ast::Block<'a>)
+			= cond:expr() p('{') block:block() p('}') { (cond, block) }
+
 		rule call_params() -> Vec<expr::Expr<'a>>
 			= args:delimited(<expr()>, <p(',')>) { args }
 
-- 
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