From 0121346e894fb0e7f60312b16986d82109e4d86b Mon Sep 17 00:00:00 2001
From: JJ
Date: Sat, 25 Nov 2023 21:07:23 -0800
Subject: compiler: preemptively fix EOF bugs in parser

---
 src/frontend/lex.rs   |   3 +-
 src/frontend/parse.rs | 215 ++++++++++++++++++++++----------------------------
 src/main.rs           |   2 +
 3 files changed, 97 insertions(+), 123 deletions(-)

diff --git a/src/frontend/lex.rs b/src/frontend/lex.rs
index 67c4ae3..f751c63 100644
--- a/src/frontend/lex.rs
+++ b/src/frontend/lex.rs
@@ -1,6 +1,7 @@
 use multipeek::multipeek;
 
-pub type Result<T> = core::result::Result<T, Box<dyn std::error::Error>>;
+use crate::*;
+
 pub struct TokenStream(Vec<Token>);
 
 impl IntoIterator for TokenStream {
diff --git a/src/frontend/parse.rs b/src/frontend/parse.rs
index eee3911..8616346 100644
--- a/src/frontend/parse.rs
+++ b/src/frontend/parse.rs
@@ -1,9 +1,10 @@
 use multipeek::multipeek;
 
-use crate::frontend::lex::*;
-use crate::frontend::ast::*;
-use crate::frontend::ast::Binding::*;
-use crate::frontend::ast::Control::*;
+use crate::*;
+use super::lex::*;
+use super::ast::*;
+use super::ast::Binding::*;
+use super::ast::Control::*;
 use Token::*;
 use Literal::*;
 use Punctuation::*;
@@ -16,13 +17,24 @@ impl Input {
         self.0.next().ok_or("end of input".into())
     }
 
-    /// Map input.peek() to return Results for use with the propagation operator
-    fn peek(&mut self) -> Result<&Token> {
-        self.0.peek().ok_or("end of input".into())
+    /// Check if the next character is an expected token, and if so, advance the iterator and return true
+    fn peek(&mut self, expected: Token) -> bool {
+        if self.0.peek() == Some(&expected) {
+            self.0.next();
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Expose input.peek() (we don't want EOF to trigger an error when peeking)
+    fn peek_opt(&mut self) -> Option<&Token> {
+        self.0.peek()
     }
 
-    fn peek_nth(&mut self, n: usize) -> Result<&Token> {
-        self.0.peek_nth(n).ok_or("end of input".into())
+    /// Expose input.peek_nth()
+    fn peek_nth(&mut self, n: usize) -> Option<&Token> {
+        self.0.peek_nth(n)
     }
 
     /// Asserts the next character to be a known token
@@ -32,12 +44,20 @@ impl Input {
             token => Err(format!("expected token {} but found {}", expected, token).into())
         }
     }
+
+    /// Allow usage of `len`
+    fn len(&self) -> usize {
+        self.0.len()
+    }
 }
 
 /// Convert a basic TokenStream into an AbstractSyntaxTree
 pub fn astify(input: TokenStream, name: &str) -> Result<Expr> {
     let mut input = Input(multipeek(input));
     let body = parse_body(&mut input)?;
+    if input.len() > 0 {
+        return Err(format!("additional tokens remaining after the body!").into());
+    }
     Ok(Expr::Binding(Module{ id: name.to_string(), body }))
 }
 
@@ -45,18 +65,16 @@ pub fn astify(input: TokenStream, name: &str) -> Result<Expr> {
 /// Body ::= Expr | ('{' Expr (';' Expr)* '}')
 fn parse_body(input: &mut Input) -> Result<Vec<Expr>> {
     let mut res = Vec::new();
-    if input.peek()? != &Sep(ScopeLeftBrace) {
+    if !input.peek(Sep(ScopeLeftBrace)) {
         res.push(parse_expr(input)?);
         return Ok(res);
     }
-    input.next()?;
-    while input.peek()? != &Sep(ScopeRightBrace) {
+    while !input.peek(Sep(ScopeRightBrace)) {
         res.push(parse_expr(input)?);
-        if input.peek()? == &Sep(Semicolon) {
-            input.next()?;
-        }
+        // consume semicolons. there doesn't *have* to be a semicolon though.
+        // this should probably be checked to be a semicolon or a right brace.
+        input.peek(Sep(Semicolon));
     }
-    input.next()?;
     Ok(res)
 }
 
@@ -64,6 +82,8 @@ fn parse_body(input: &mut Input) -> Result<Vec<Expr>> {
 ///   Block | Static | For | While | Loop | If | When | Try | Match
 fn parse_expr(input: &mut Input) -> Result<Expr> {
     use Keyword::*;
+    // Note that this match consumes, as peeking is redundant.
+    // This is why subsequent functions do not check for their leading keyword, i.e. 'let'
     match input.next()? {
         Key(word) => match word {
             Pub => {
@@ -116,7 +136,7 @@ fn parse_var(input: &mut Input) -> Result<Expr> {
     let id = parse_pattern(input)?;
     let kind = parse_annotation(input)?;
     let mut value = None;
-    if input.next()? != Sep(Equals) {
+    if input.peek(Sep(Equals)) {
         value = Some(Box::new(parse_expr(input)?));
     }
     Ok(Expr::Binding(Var { id, kind, value }))
@@ -131,29 +151,26 @@ fn parse_const(input: &mut Input, public: bool) -> Result<Expr> {
     Ok(Expr::Binding(Const { public, id, kind, value }))
 }
 
-/// Annotation ::= (':' TypeDesc)?
+/// Annotation ::= (':' Type)?
 fn parse_annotation(input: &mut Input) -> Result<Option<Type>> {
-    let mut kind = None;
-    if input.peek()? == &Sep(Colon) {
-        input.next()?;
-        kind = Some(parse_type(input)?);
+    if input.peek(Sep(Colon)) {
+        Ok(Some(parse_type(input)?))
+    } else {
+        Ok(None)
     }
-    Ok(kind)
 }
 
-/// `Func ::= 'pub'? 'func' Ident ('[' Parameters ']')? ('(' Parameters ')')? (':' TypeDesc) '=' Body`
+/// `Func ::= 'pub'? 'func' Ident ('[' Parameters ']')? ('(' Parameters ')')? Annotation '=' Body`
 fn parse_func(input: &mut Input, public: bool) -> Result<Expr> {
     let effect = None;
     let id = parse_ident(input)?;
     let mut generics = Vec::new();
-    if input.peek()? == &Sep(GenericLeftBracket) {
-        input.next()?;
+    if input.peek(Sep(GenericLeftBracket)) {
         generics = parse_parameters(input)?;
         input.then(Sep(GenericRightBracket))?;
     }
     let mut parameters = Vec::new();
-    if input.peek()? == &Sep(FuncLeftParen) {
-        input.next()?; // todo: rewrite to map over an input
+    if input.peek(Sep(FuncLeftParen)) { // todo: rewrite to map over an input
         // let temp_parameters = parse_parameters(input)?;
         // if temp_parameters.last().is_none() {
         //     return Err("expected a type annotation on the last function parameter".into());
@@ -166,8 +183,7 @@ fn parse_func(input: &mut Input, public: bool) -> Result<Expr> {
         } else {
             stack.push(id);
         }
-        while input.peek()? == &Sep(Comma) {
-            input.next()?;
+        while input.peek(Sep(Comma)) {
             let (id, kind) = parse_parameter(input)?;
             stack.push(id);
             if kind.is_some() {
@@ -183,8 +199,7 @@ fn parse_func(input: &mut Input, public: bool) -> Result<Expr> {
         input.then(Sep(FuncRightParen))?;
     }
     let mut kind = Type::Void;
-    if input.peek()? == &Sep(Colon) {
-        input.next()?;
+    if input.peek(Sep(Colon)) {
         kind = parse_type(input)?;
     }
     input.then(Sep(Equals))?;
@@ -192,24 +207,21 @@ fn parse_func(input: &mut Input, public: bool) -> Result<Expr> {
     Ok(Expr::Binding(Func { public, effect, id, generics, parameters, kind, body }))
 }
 
-/// `Macro ::= 'pub'? 'macro' Ident ('[' Paremeters ']')? ('(' Paremeters ')')? (':' TypeDesc) '=' Body`
+/// `Macro ::= 'pub'? 'macro' Ident ('[' Parameters ']')? ('(' Parameters ')')? (':' Type) '=' Body`
 fn parse_macro(input: &mut Input, public: bool) -> Result<Expr> {
     let id = parse_ident(input)?;
     let mut generics = Vec::new();
-    if input.peek()? == &Sep(GenericLeftBracket) {
-        input.next()?;
+    if input.peek(Sep(GenericLeftBracket)) {
         generics = parse_parameters(input)?;
         input.then(Sep(GenericRightBracket))?;
     }
     let mut parameters = Vec::new();
-    if input.peek()? == &Sep(FuncLeftParen) {
-        input.next()?;
+    if input.peek(Sep(FuncLeftParen)) {
         parameters = parse_parameters(input)?;
         input.then(Sep(FuncRightParen))?;
     }
     let mut kind = None;
-    if input.peek()? == &Sep(Colon) {
-        input.next()?;
+    if input.peek(Sep(Colon)) {
         kind = Some(parse_type(input)?);
     }
     input.then(Sep(Equals))?;
@@ -221,8 +233,7 @@ fn parse_macro(input: &mut Input, public: bool) -> Result<Expr> {
 fn parse_typedecl(input: &mut Input, public: bool) -> Result<Expr> {
     let id = parse_ident(input)?;
     let mut generics = Vec::new();
-    if input.peek()? == &Sep(GenericLeftBracket) {
-        input.next()?;
+    if input.peek(Sep(GenericLeftBracket)) {
         generics = parse_parameters(input)?;
         input.then(Sep(GenericRightBracket))?;
     }
@@ -235,8 +246,7 @@ fn parse_typedecl(input: &mut Input, public: bool) -> Result<Expr> {
 fn parse_parameter(input: &mut Input) -> Result<(Id, Option<Type>)> {
     let id = parse_ident(input)?;
     let mut kind = None;
-    if input.peek()? == &Sep(Colon) {
-        input.next()?;
+    if input.peek(Sep(Colon)) {
         kind = Some(parse_type(input)?);
     }
     Ok((id, kind))
@@ -246,8 +256,7 @@ fn parse_parameter(input: &mut Input) -> Result<(Id, Option<Type>)> {
 fn parse_parameters(input: &mut Input) -> Result<Vec<(Id, Option<Type>)>> {
     let mut res = Vec::new();
     res.push(parse_parameter(input)?);
-    while input.peek()? == &Sep(Comma) {
-        input.next()?;
+    while input.peek(Sep(Comma)) {
         res.push(parse_parameter(input)?);
     }
     Ok(res)
@@ -255,18 +264,10 @@ fn parse_parameters(input: &mut Input) -> Result<Vec<(Id, Option<Type>)>> {
 
 /// `Mod ::= 'pub'? 'mod' Ident ':' Body`
 fn parse_mod(input: &mut Input, public: bool) -> Result<Expr> {
-    match input.next()? {
-        Word(id) => {
-            match input.next()? {
-                Sep(Colon) => {
-                    let body = parse_body(input)?;
-                    Ok(Expr::Binding(Module { id, body }))
-                },
-                _ => return Err("unexpected token following mod label".into()),
-            }
-        },
-        _ => return Err("unexpected thing following mod keyword".into()),
-    }
+    let id = parse_ident(input)?;
+    input.then(Sep(Colon))?;
+    let body = parse_body(input)?;
+    Ok(Expr::Binding(Module { id, body }))
 }
 
 /// `Use ::= 'use' Ident ('/' Ident)* ('/' (('[' Ident (',' Ident)* ']') | '*'))?`
@@ -326,13 +327,11 @@ fn parse_loop(input: &mut Input) -> Result<Expr> {
 fn parse_if(input: &mut Input) -> Result<Expr> {
     let mut branches = Vec::new();
     branches.push(parse_cond_branch(input)?);
-    while input.peek()? == &Key(Keyword::Elif) {
-        input.next()?;
+    while input.peek(Key(Keyword::Elif)) {
         branches.push(parse_cond_branch(input)?);
     }
     let mut else_body = None;
-    if input.peek()? == &Key(Keyword::Else) {
-        input.next()?;
+    if input.peek(Key(Keyword::Else)) {
         else_body = Some(parse_body(input)?);
     }
     Ok(Expr::Control(If { branches, else_body }))
@@ -342,13 +341,11 @@ fn parse_if(input: &mut Input) -> Result<Expr> {
 fn parse_when(input: &mut Input) -> Result<Expr> {
     let mut branches = Vec::new();
     branches.push(parse_cond_branch(input)?);
-    while input.peek()? == &Key(Keyword::Elif) {
-        input.next()?;
+    while input.peek(Key(Keyword::Elif)) {
         branches.push(parse_cond_branch(input)?);
     }
     let mut else_body = None;
-    if input.peek()? == &Key(Keyword::Else) {
-        input.next()?;
+    if input.peek(Key(Keyword::Else)) {
         input.then(Sep(Colon))?;
         else_body = Some(parse_body(input)?);
     }
@@ -365,17 +362,15 @@ fn parse_cond_branch(input: &mut Input) -> Result<CondBranch> {
     Ok(CondBranch { cond, body })
 }
 
-/// `Try ::= 'try' ':' Body ('except' Exception (',' Exception)* ':' Body) ('finally' ':' Body)?`
+/// `Try ::= 'try' ':' Body ('except' Exception (',' Exception)* ':' Body)* ('finally' ':' Body)?`
 fn parse_try(input: &mut Input) -> Result<Expr> {
     input.then(Sep(Colon))?;
     let body = parse_body(input)?;
     let mut catches = Vec::new();
-    while input.peek()? == &Key(Keyword::Catch) {
-        input.next()?;
+    while input.peek(Key(Keyword::Catch)) {
         let mut exceptions = Vec::new();
         exceptions.push(parse_catch_exception(input)?);
-        while input.peek()? == &Sep(Comma) {
-            input.next()?;
+        while input.peek(Sep(Comma)) {
             exceptions.push(parse_catch_exception(input)?);
         }
         input.then(Sep(Colon))?;
@@ -383,8 +378,7 @@ fn parse_try(input: &mut Input) -> Result<Expr> {
         catches.push(CatchBranch { exceptions, body });
     }
     let mut finally = None;
-    if input.peek()? == &Key(Keyword::Finally) {
-        input.next()?;
+    if input.peek(Key(Keyword::Finally)) {
         input.then(Sep(Colon))?;
         finally = Some(parse_body(input)?);
     }
@@ -395,8 +389,7 @@ fn parse_try(input: &mut Input) -> Result<Expr> {
 fn parse_catch_exception(input: &mut Input) -> Result<(Id, Option<Id>)> {
     let id = parse_ident(input)?;
     let mut alias = None;
-    if input.peek()? == &Key(Keyword::As) {
-        input.next()?;
+    if input.peek(Key(Keyword::As)) {
         alias = Some(parse_ident(input)?);
     }
     Ok((id, alias))
@@ -406,17 +399,14 @@ fn parse_catch_exception(input: &mut Input) -> Result<(Id, Option<Id>)> {
 fn parse_match(input: &mut Input) -> Result<Expr> {
     let item = parse_pattern(input)?; // fixme
     let mut branches = Vec::new();
-    while input.peek()? == &Key(Keyword::Of) {
-        input.next()?;
+    while input.peek(Key(Keyword::Of)) {
         let mut patterns = Vec::new();
         patterns.push(parse_pattern(input)?);
-        while input.peek()? == &Sep(Comma) {
-            input.next()?;
+        while input.peek(Sep(Comma)) {
             patterns.push(parse_pattern(input)?);
         }
         let mut guard = None;
-        if input.peek()? == &Key(Keyword::Where) {
-            input.next()?;
+        if input.peek(Key(Keyword::Where)) {
             guard = Some(parse_expr(input)?)
         }
         input.then(Sep(Colon))?;
@@ -449,11 +439,9 @@ fn parse_type(input: &mut Input) -> Result<Type> {
         },
         Word(id) => {
             let mut generics = Vec::new();
-            if input.peek()? == &Sep(GenericLeftBracket) {
-                input.next()?;
+            if input.peek(Sep(GenericLeftBracket)) {
                 generics.push(parse_type(input)?);
-                while input.peek()? == &Sep(Comma) {
-                    input.next()?;
+                while input.peek(Sep(Comma)) {
                     generics.push(parse_type(input)?);
                 }
                 input.then(Sep(GenericRightBracket))?;
@@ -467,11 +455,9 @@ fn parse_type(input: &mut Input) -> Result<Type> {
 /// `StructType ::= 'struct' ('[' Ident ':' Type (',' Ident ':' Type)* ']')?`
 fn parse_struct_type(input: &mut Input) -> Result<Type> {
     let mut res = Vec::new();
-    if input.peek()? == &Sep(GenericLeftBracket) {
-        input.next()?;
+    if input.peek(Sep(GenericLeftBracket)) {
         res.push(parse_struct_field(input)?);
-        while input.peek()? == &Sep(Comma) {
-            input.next()?;
+        while input.peek(Sep(Comma)) {
             res.push(parse_struct_field(input)?);
         }
         input.then(Sep(GenericRightBracket))?;
@@ -489,11 +475,9 @@ fn parse_struct_field(input: &mut Input) -> Result<(Id, Box<Type>)> {
 /// `TupleType ::= 'tuple' ('[' (Ident ':')? Type (',' (Ident ':')? Type)* ']')?`
 fn parse_tuple_type(input: &mut Input) -> Result<Type> {
     let mut res = Vec::new();
-    if input.peek()? == &Sep(GenericLeftBracket) {
-        input.next()?;
+    if input.peek(Sep(GenericLeftBracket)) {
         res.push(parse_tuple_field(input)?);
-        while input.peek()? == &Sep(Comma) {
-            input.next()?;
+        while input.peek(Sep(Comma)) {
             res.push(parse_tuple_field(input)?);
         }
         input.then(Sep(GenericRightBracket))?;
@@ -501,10 +485,12 @@ fn parse_tuple_type(input: &mut Input) -> Result<Type> {
     Ok(Type::Tuple(res))
 }
 
+// annoyingly complex to parse. `TupleField ::= (Ident ':')? Type`
 fn parse_tuple_field(input: &mut Input) -> Result<(Option<Id>, Box<Type>)> {
-    match input.peek()?.clone() { // huh???
-        Word(id) if input.peek_nth(1)? == &Sep(Colon) => {
+    match input.peek_opt().clone() {
+        Some(Word(id)) if input.peek_nth(1) == Some(&Sep(Colon)) => {
             input.next()?;
+            input.then(Sep(Colon))?;
             Ok((Some(id.to_string()), Box::new(parse_type(input)?)))
         },
         _ => Ok((None, Box::new(parse_type(input)?)))
@@ -514,11 +500,9 @@ fn parse_tuple_field(input: &mut Input) -> Result<(Option<Id>, Box<Type>)> {
 /// `EnumType ::= 'enum' ('[' Ident ('=' Pattern)? (Ident ('=' Pattern)?)* ']')?`
 fn parse_enum_type(input: &mut Input) -> Result<Type> {
     let mut res = Vec::new();
-    if input.peek()? == &Sep(GenericLeftBracket) {
-        input.next()?;
+    if input.peek(Sep(GenericLeftBracket)) {
         res.push(parse_enum_variant(input)?);
-        while input.peek()? == &Sep(Comma) {
-            input.next()?;
+        while input.peek(Sep(Comma)) {
             res.push(parse_enum_variant(input)?);
         }
         input.then(Sep(GenericRightBracket))?;
@@ -529,8 +513,7 @@ fn parse_enum_type(input: &mut Input) -> Result<Type> {
 fn parse_enum_variant(input: &mut Input) -> Result<(Id, Option<Pattern>)> {
     let id = parse_ident(input)?;
     let mut kind = None;
-    if input.peek()? == &Sep(Equals) {
-        input.next()?;
+    if input.peek(Sep(Equals)) {
         kind = Some(parse_pattern(input)?);
     }
     Ok((id, kind))
@@ -539,11 +522,9 @@ fn parse_enum_variant(input: &mut Input) -> Result<(Id, Option<Pattern>)> {
 /// `UnionType ::= 'union' ('[' Ident (':' Type)? (',' Ident (':' Type)?)* ']')?`
 fn parse_union_type(input: &mut Input) -> Result<Type> {
     let mut res = Vec::new();
-    if input.peek()? == &Sep(GenericLeftBracket) {
-        input.next()?;
+    if input.peek(Sep(GenericLeftBracket)) {
         res.push(parse_union_variant(input)?);
-        while input.peek()? == &Sep(Comma) {
-            input.next()?;
+        while input.peek(Sep(Comma)) {
             res.push(parse_union_variant(input)?);
         }
         input.then(Sep(GenericRightBracket))?;
@@ -554,8 +535,7 @@ fn parse_union_type(input: &mut Input) -> Result<Type> {
 fn parse_union_variant(input: &mut Input) -> Result<(Id, Box<Type>)> {
     let id = parse_ident(input)?;
     let mut kind = Box::new(Type::Alias { id: "unit".to_string(), generics: Vec::new() });
-    if input.peek()? == &Sep(Colon) {
-        input.next()?;
+    if input.peek(Sep(Colon)) {
         kind = Box::new(parse_type(input)?);
     }
     Ok((id, kind))
@@ -564,11 +544,9 @@ fn parse_union_variant(input: &mut Input) -> Result<(Id, Box<Type>)> {
 /// `Interface ::= 'interface' ('[' Signature (',' Signature)* ']')?`
 fn parse_interface(input: &mut Input) -> Result<Type> {
     let mut res = Vec::new();
-    if input.peek()? == &Sep(GenericLeftBracket) {
-        input.next()?;
+    if input.peek(Sep(GenericLeftBracket)) {
         res.push(parse_signature(input)?);
-        while input.peek()? == &Sep(Comma) {
-            input.next()?;
+        while input.peek(Sep(Comma)) {
             res.push(parse_signature(input)?);
         }
         input.then(Sep(GenericRightBracket))?;
@@ -581,24 +559,20 @@ fn parse_signature(input: &mut Input) -> Result<Sig> {
     let effect = None;
     let id = parse_ident(input)?;
     let mut generics = Vec::new();
-    if input.peek()? == &Sep(GenericLeftBracket) {
-        input.next()?;
+    if input.peek(Sep(GenericLeftBracket)) {
         generics = parse_parameters(input)?;
         input.then(Sep(GenericRightBracket))?;
     }
     let mut parameters = Vec::new();
-    if input.peek()? == &Sep(FuncLeftParen) {
-        input.next()?;
+    if input.peek(Sep(FuncLeftParen)) {
         parameters.push(parse_type(input)?);
-        if input.peek()? == &Sep(Comma) {
-            input.next()?;
+        if input.peek(Sep(Comma)) {
             parameters.push(parse_type(input)?);
         }
         input.then(Sep(FuncRightParen))?;
     }
     let mut kind = None;
-    if input.peek()? == &Sep(Colon) {
-        input.next()?;
+    if input.peek(Sep(Colon)) {
         kind = Some(parse_type(input)?);
     }
     Ok(Sig { effect, id, generics, parameters, kind })
@@ -606,7 +580,7 @@ fn parse_signature(input: &mut Input) -> Result<Sig> {
 
 /// `WrappedType ::= Type | ('[' Type ']')`
 fn parse_wrapped_type(input: &mut Input) -> Result<Type> {
-    if input.next()? == Sep(GenericLeftBracket) {
+    if input.peek(Sep(GenericLeftBracket)) {
         let result = parse_type(input)?;
         input.then(Sep(GenericRightBracket))?;
         Ok(result)
@@ -618,9 +592,6 @@ fn parse_wrapped_type(input: &mut Input) -> Result<Type> {
 /// Pattern ::= Literal | Ident | '(' Pattern (',' Pattern)* ')' | Ident '(' Pattern (',' Pattern)* ')'
 fn parse_pattern(input: &mut Input) -> Result<Pattern> { todo!() }
 
-/// Literal ::= Char | String | Number | Float
-fn parse_literal(input: &mut Input) -> Result<Pattern> { todo!() }
-
 fn parse_ident(input: &mut Input) -> Result<Id> {
     match input.next()? {
         Word(id) => Ok(id),
diff --git a/src/main.rs b/src/main.rs
index d7c995c..ad8b5cf 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,4 +3,6 @@
 
 mod frontend;
 
+pub type Result<T> = core::result::Result<T, Box<dyn std::error::Error>>;
+
 fn main() {}
-- 
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