From b4e9ae520d3e68579f1c6aa04f937a20262d61b0 Mon Sep 17 00:00:00 2001
From: Garrit Franke <garrit@slashdev.space>
Date: Sat, 20 Feb 2021 21:09:54 +0100
Subject: [PATCH] feat: parser implementation of match

---
 src/generator/c.rs      |  1 +
 src/generator/js.rs     |  1 +
 src/parser/node_type.rs |  3 +++
 src/parser/parser.rs    |  6 ++++++
 src/parser/rules.rs     | 42 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 53 insertions(+)

diff --git a/src/generator/c.rs b/src/generator/c.rs
index 02da8ea..ad080e8 100644
--- a/src/generator/c.rs
+++ b/src/generator/c.rs
@@ -112,6 +112,7 @@ fn generate_statement(statement: Statement) -> String {
         Statement::For(_ident, _expr, _body) => todo!(),
         Statement::Continue => todo!(),
         Statement::Break => todo!(),
+        Statement::Match(_, _) => todo!(),
     };
 
     format!("{}\n", state)
diff --git a/src/generator/js.rs b/src/generator/js.rs
index 6f174bf..d777344 100644
--- a/src/generator/js.rs
+++ b/src/generator/js.rs
@@ -103,6 +103,7 @@ fn generate_statement(statement: Statement) -> String {
         Statement::For(ident, expr, body) => generate_for_loop(ident, expr, *body),
         Statement::Continue => generate_continue(),
         Statement::Break => generate_break(),
+        Statement::Match(_, _) => todo!(),
     };
 
     format!("{};\n", state)
diff --git a/src/parser/node_type.rs b/src/parser/node_type.rs
index bc0940f..e680e13 100644
--- a/src/parser/node_type.rs
+++ b/src/parser/node_type.rs
@@ -20,6 +20,8 @@ use std::collections::HashMap;
 /// Table that contains all symbol and its types
 pub type SymbolTable = HashMap<String, Option<Type>>;
 
+pub type MatchArm = (Expression, Statement);
+
 #[derive(Debug)]
 pub struct Program {
     pub func: Vec<Function>,
@@ -97,6 +99,7 @@ pub enum Statement {
     If(Expression, Box<Statement>, Option<Box<Statement>>),
     While(Expression, Box<Statement>),
     For(Variable, Expression, Box<Statement>),
+    Match(Expression, Vec<MatchArm>),
     Break,
     Continue,
     Exp(Expression),
diff --git a/src/parser/parser.rs b/src/parser/parser.rs
index 58e5751..9184448 100644
--- a/src/parser/parser.rs
+++ b/src/parser/parser.rs
@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+use crate::lexer::Position;
 use crate::lexer::Keyword;
 use crate::lexer::{Token, TokenKind};
 use crate::parser::infer::infer;
@@ -126,6 +127,11 @@ impl Parser {
         }
     }
 
+    pub(super) fn make_error_msg(&mut self, pos: Position, msg: String) -> String {
+        let pos_string = format!("{}:{}", pos.line, pos.offset);
+        format!("ERROR: {}\nAt {}", msg, pos_string)
+    }
+
     pub(super) fn prev(&mut self) -> Option<Token> {
         self.prev.clone()
     }
diff --git a/src/parser/rules.rs b/src/parser/rules.rs
index 4334764..3086931 100644
--- a/src/parser/rules.rs
+++ b/src/parser/rules.rs
@@ -165,6 +165,7 @@ impl Parser {
             TokenKind::Keyword(Keyword::Break) => self.parse_break(),
             TokenKind::Keyword(Keyword::Continue) => self.parse_continue(),
             TokenKind::Keyword(Keyword::For) => self.parse_for_loop(),
+            TokenKind::Keyword(Keyword::Match) => self.parse_match_statement(),
             TokenKind::Identifier(_) => {
                 let ident = self.match_identifier()?;
                 let expr = if self.peek_token(TokenKind::Dot).is_ok() {
@@ -457,6 +458,47 @@ impl Parser {
         ))
     }
 
+    fn parse_match_statement(&mut self) -> Result<Statement, String> {
+        self.match_keyword(Keyword::Match)?;
+        let subject = self.parse_expression()?;
+        self.match_token(TokenKind::CurlyBracesOpen)?;
+        let mut arms: Vec<MatchArm> = Vec::new();
+
+        // Used to mitigate multiple default cases were defined
+        let mut has_default = false;
+        loop {
+            let next = self.peek()?;
+            match next.kind {
+                TokenKind::Literal(_) | TokenKind::Identifier(_) => {
+                    arms.push(self.parse_match_arm()?)
+                }
+                TokenKind::Keyword(Keyword::Default) => {
+                    if has_default {
+                        return Err(self.make_error_msg(
+                            next.pos,
+                            "Multiple defaults are not allowed".to_string(),
+                        ));
+                    }
+                    has_default = true;
+                    arms.push(self.parse_match_arm()?);
+                }
+                TokenKind::CurlyBracesClose => break,
+                _ => return Err(self.make_error_msg(next.pos, "Illegal token".to_string()))
+            }
+        }
+        self.match_token(TokenKind::CurlyBracesClose)?;
+        Ok(Statement::Match(subject, arms))
+    }
+
+    fn parse_match_arm(&mut self) -> Result<MatchArm, String> {
+        let expr = self.parse_expression()?;
+        self.match_token(TokenKind::ArrowRight)?;
+        let statement = self.parse_statement()?;
+
+        Ok((expr, statement))
+
+    }
+
     fn parse_conditional_statement(&mut self) -> Result<Statement, String> {
         self.match_keyword(Keyword::If)?;
         let condition = self.parse_expression()?;