From f14677b6f5a81a5cf885f31c687091106025406b Mon Sep 17 00:00:00 2001
From: Moritz Gmeiner <moritz@gmeiner.net>
Date: Wed, 14 Aug 2024 12:36:36 +0200
Subject: [PATCH] fnished first draft of expression parser

---
 lib/parser.ml | 47 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 38 insertions(+), 9 deletions(-)

diff --git a/lib/parser.ml b/lib/parser.ml
index 10dbb90..ab384f3 100644
--- a/lib/parser.ml
+++ b/lib/parser.ml
@@ -22,6 +22,18 @@ module State = struct
   let advance_if state tt =
     if (peek state).token_type == tt then (true, advance state) else (false, state)
 
+  let consume state tt =
+    if (peek state).token_type == tt then advance state
+    else
+      let state =
+        append_error
+          (Printf.sprintf "Unexpected %s, expected %s"
+             (show_token_type (peek state).token_type)
+             (show_token_type tt))
+          (peek state).pos state
+      in
+      state
+
   let matches state tts =
     let f = ( == ) (peek state).token_type in
     Array.fold_left (fun acc tt -> acc || f tt) false tts
@@ -40,10 +52,27 @@ module State = struct
     (Array.of_list (List.rev !out_list_rev), !state_ref)
 
   let primary (state : state) : expr * state =
-    let token, state = next state in
-    (make_string @@ show_token_type token.token_type, state)
+    match (peek state).token_type with
+    | Number x -> (make_number x, advance state)
+    | String s -> (make_string s, advance state)
+    | True -> (make_bool true, advance state)
+    | False -> (make_bool false, advance state)
+    | Nil -> (make_nil (), advance state)
+    | tt ->
+        ( make_nil (),
+          append_error
+            (Printf.sprintf "Unexpected %s, expected valid expression" (show_token_type tt))
+            (peek state).pos state )
 
-  let rec neg_not (state : state) : expr * state =
+  let rec grouping (state : state) : expr * state =
+    if matches state [| LeftParen |] then
+      let state = advance state in
+      let expr, state = expression state in
+      let state = consume state RightParen in
+      (expr, state)
+    else primary state
+
+  and neg_not (state : state) : expr * state =
     if matches state [| Bang; Minus |] then
       let token, state = next state in
       let expr, state = neg_not state in
@@ -55,9 +84,9 @@ module State = struct
       in
       let expr = make_unary op expr in
       (expr, state)
-    else primary state
+    else grouping state
 
-  let mul_or_div (state : state) : expr * state =
+  and mul_or_div (state : state) : expr * state =
     let expr, state = neg_not state in
     let exprs_tokens, state = collect_chain state [| Star; Slash |] neg_not in
     let f acc (expr, token) =
@@ -72,7 +101,7 @@ module State = struct
     let expr = Array.fold_left f expr exprs_tokens in
     (expr, state)
 
-  let sum_or_diff (state : state) : expr * state =
+  and sum_or_diff (state : state) : expr * state =
     let expr, state = mul_or_div state in
     let exprs_tokens, state = collect_chain state [| Plus; Minus |] mul_or_div in
     let f acc (expr, token) =
@@ -87,7 +116,7 @@ module State = struct
     let expr = Array.fold_left f expr exprs_tokens in
     (expr, state)
 
-  let inequality (state : state) : expr * state =
+  and inequality (state : state) : expr * state =
     (* TODO: maybe rework to only have Less and Greater as ops; performance? *)
     let expr, state = sum_or_diff state in
     let exprs_tokens, state =
@@ -107,7 +136,7 @@ module State = struct
     let expr = Array.fold_left f expr exprs_tokens in
     (expr, state)
 
-  let equality (state : state) : expr * state =
+  and equality (state : state) : expr * state =
     let expr, state = inequality state in
     let exprs_tokens, state = collect_chain state [| EqualEqual; BangEqual |] inequality in
     let f acc (expr, token) =
@@ -121,7 +150,7 @@ module State = struct
     let expr = Array.fold_left f expr exprs_tokens in
     (expr, state)
 
-  let expression (state : state) : expr * state = equality state
+  and expression (state : state) : expr * state = equality state
 end
 
 let parse (tokens : token list) : parse_result =