From d841f5d2c14812952aea4c26950190fb65251ed9 Mon Sep 17 00:00:00 2001
From: Natapat Samutpong <natapat.samutpong@gmail.com>
Date: Sat, 12 Feb 2022 20:17:13 +0700
Subject: [PATCH] if else and commenting

---
 example/hello_world.hyc | 14 +++++++-------
 src/front/lex.rs        | 18 +++++++++++++++---
 src/front/parser.rs     | 19 +++++++++++++++++++
 3 files changed, 41 insertions(+), 10 deletions(-)

diff --git a/example/hello_world.hyc b/example/hello_world.hyc
index 062bc84..68f9bad 100644
--- a/example/hello_world.hyc
+++ b/example/hello_world.hyc
@@ -1,10 +1,10 @@
-func join :: (a, b) = {
-    let result :: String = from(a, b);
-    return result
+// user defined function
+func foo :: (a, b) = {
+    return a;
 };
 
+// entry point
 func main :: () = {
-    let foo :: String = join("f", "oo");
-    print(foo);
-    return 0
-};
\ No newline at end of file
+    // if else in variable definition
+    let cond_str :: String = if true { return "t" } else { return "f" };
+};
diff --git a/src/front/lex.rs b/src/front/lex.rs
index 97aa658..8dbb9d8 100644
--- a/src/front/lex.rs
+++ b/src/front/lex.rs
@@ -1,6 +1,6 @@
 use nom::{
     branch::alt,
-    bytes::complete::{tag, take},
+    bytes::complete::{tag, take, take_until},
     character::complete::{multispace0, alphanumeric1, alpha1, digit1},
     combinator::{map, map_res, recognize},
     IResult,
@@ -119,15 +119,27 @@ fn lex_illegal(input: &Bytes) -> IResult<&Bytes, Token> {
     map(take(1usize), |_| Token::Illegal)(input)
 }
 
+fn lex_comment(input: &Bytes) -> IResult<&Bytes, ()> {
+    let (i1, c1) = take(2usize)(input)?;
+    if c1.as_bytes() == b"//" {
+        let (i2, _) = take_until("\n")(i1)?;
+        let (i3, _) = take(1usize)(i2)?;
+        let (i4, _) = multispace0(i3)?;
+        let (i5, _) = lex_comment(i4)?;
+        Ok((i5, ()))
+    } else { Ok((input, ())) }
+}
+
 // Tokens
 fn lex_token(input: &Bytes) -> IResult<&Bytes, Token> {
+    let (i1, _) = lex_comment(input)?;
     alt((
         lex_operator_punctuation,
-        lex_string,
         lex_reserved_identifier,
+        lex_string,
         lex_integer,
         lex_illegal,
-    ))(input)
+    ))(i1)
 }
 
 fn lex_tokens(input: &Bytes) -> IResult<&Bytes, Vec<Token>> {
diff --git a/src/front/parser.rs b/src/front/parser.rs
index 8b7bf4a..2695cde 100644
--- a/src/front/parser.rs
+++ b/src/front/parser.rs
@@ -22,6 +22,8 @@ macro_rules! tag_token (
 tag_token!(tag_let, Token::Let);
 tag_token!(tag_func, Token::Func);
 tag_token!(tag_return, Token::Return);
+tag_token!(tag_if, Token::If);
+tag_token!(tag_else, Token::Else);
 
 tag_token!(tag_assign, Token::Assign);
 tag_token!(tag_typehint, Token::Typehint);
@@ -71,6 +73,7 @@ fn parse_atom_expr(input: Tokens) -> IResult<Tokens, Expr> {
     alt((
         parse_literal_expr,
         parse_ident_expr,
+        parse_if_expr,
     ))(input)
 }
  
@@ -130,6 +133,22 @@ fn parse_expr(input: Tokens, precedence: Precedence, left: Expr) -> IResult<Toke
     }
 }
 
+fn parse_if_expr(input: Tokens) -> IResult<Tokens, Expr> {
+    map(
+        tuple((
+            tag_if,
+            parse_expr_lowest,
+            parse_block_stmt,
+            parse_else_expr,
+        )),
+        |(_, cond, then, else_)| Expr::If { cond: Box::new(cond), then, else_ },
+    )(input)
+}
+
+fn parse_else_expr(input: Tokens) -> IResult<Tokens, Option<Program>> {
+    opt(preceded(tag_else, parse_block_stmt))(input)
+}
+
 fn parse_comma_exprs(input: Tokens) -> IResult<Tokens, Expr> {
     preceded(tag_comma, parse_expr_lowest)(input)
 }