corelang/new_parse.cpp

function Token *
token_get(S64 i = 0){ Get_Ctx(Parse_Ctx);
  i += ctx->token_iter;
  if(i >= ctx->tokens.len){
    return &ctx->empty_token;
  }
  
  Token *result = &ctx->tokens[i];
  return result;
}

function Token *
token_next(){ Get_Ctx(Parse_Ctx);
  Token *token = token_get();
  ctx->token_iter++;
  return token;
}

function Token *
token_is(Token_Kind kind){
  Token *token = token_get();
  if(token->kind == kind){
    return token;
  }
  return 0;
}

function Token *
token_match(Token_Kind kind){
  Token *token = token_get();
  if(token->kind == kind){
    return token_next();
  }
  return 0;
}

function Token *
token_match_keyword(Intern_String string){
  Token *token = token_get();
  if(token->kind == TK_Keyword){
    if(string.str == token->intern_val.str){
      token = token_next();
      return token;
    }
  }
  return 0;
}

function void
parsing_error(Token *token, const char *str, ...){ 
  Set_Scratch();
  STRING_FMT(imp_get(), str, string);
  
  // @Note(Krzosa): Print nice error message
  printf("\nError: %s", string.str);
  if(token){
    printf(" %s:%d\n", token->file.str, (S32)token->line);
    
    // @Note(Krzosa): Print error line
    {
      int i = 0;
      while(token->line_begin[i]!='\n' && token->line_begin[i]!=0) i++;
      printf("%.*s\n", i, token->line_begin);
      
      // @Note(Krzosa): Print error marker
      int token_i = token->str - token->line_begin;
      for(int i = 0; i < token_i-2; i++) printf(" ");
      printf("^^^^^^\n");
    }
  }
  
  __debugbreak();
}

function Token *
token_expect(Token_Kind kind){
  Token *token = token_get();
  if(token->kind == kind){
    token = token_next();
    return token;
  }
  parsing_error(token, "Expected token of kind: [%s], got instead token of kind: [%s]", token_kind_string(kind).str, token_kind_string(token->kind).str);
  return 0;
}

//-----------------------------------------------------------------------------
// Expression parsing
//-----------------------------------------------------------------------------
/*
add = [+-]
mul = [/%*]
compare = == | != | >= | > | <= | <
logical = [&|^] | && | ||
unary = [&*-!~+] | ++ | --

atom_expr = Int 
| Float 
| String 
| Identifier
| 'cast' '(' typespec ',' expr ')'
| 'size_type' '(' typespec ')'
| 'size_expr' '(' expr ')'
| '{' compound_expr '}'
| '(' expr ')' 
| '(' ':' typespec ')' '{' compound_expr '}'
postfix_expr = atom_expr ('[' expr ']' | '.' Identifier | ++ | -- | '(' expr_list ')')*
unary_expr = unary ? unary_expr : atom_expr
mul_expr = atom_expr (mul atom_expr)*
add_expr = mul_expr (add mul_expr)*
logical_expr = add_expr (logical add_expr)*
compare_expr = logical_expr (compare logical_expr)*
ternary_expr = compare_expr ('?' ternary_expr ':' ternary_expr)?
expr = logical_expr

Compound literals
- (:[23]*Type){}
 - Type{}
- { }
*/
function Ast_Expr *parse_expr(S64 rbp = 0);

function Ast_Expr *
parse_expr_nud(Token *token){
  switch(token->kind){
    case TK_StringLit: return ast_expr_string(token, token->intern_val);
    case TK_Identifier: return ast_expr_identifier(token, token->intern_val);
    case TK_Integer: return ast_expr_integer(token, token->int_val);
    case TK_OpenParen: {Ast_Expr *result = parse_expr(); token_expect(TK_CloseParen); return result;}
    default: parsing_error(token, "Unexpected token of kind: [%s] in expression", token_kind_string(token->kind).str); return 0;
  }
}

function S64
op_precedence(Token_Kind kind){ Get_Ctx(Parse_Ctx);
  S64 result = ctx->pt[kind];
  return result;
}

function Ast_Expr *
parse_expr_led(Token *op, Ast_Expr *left){
  enum{ Left_Associative, Right_Associative };
  S64 assoc = Left_Associative;
  Ast_Expr *right = parse_expr(op_precedence(op->kind) - assoc);
  switch(op->kind){
    case TK_Add: case TK_Mul: case TK_Sub: case TK_Div: return ast_expr_binary(left, right, op);
    default: parsing_error(op, "Unexpected token of kind: [%s] in expression", token_kind_string(op->kind).str); return 0;
  }
}

function Ast_Expr *
parse_expr(S64 rbp){
  Token *token = token_next();
  Ast_Expr *left = parse_expr_nud(token);
  while(rbp < op_precedence(token_get()->kind)){
    token = token_next();
    left  = parse_expr_led(token, left);
  }
  return left;
}

function S64
expr_eval(Ast_Expr *expr){
  switch(expr->kind){
    case AK_Expr_Int: return expr->int_val;
    case AK_Expr_Binary : {
      S64 left = expr_eval(expr->binary.left);
      S64 right = expr_eval(expr->binary.right);
      switch(expr->binary.op){
        case TK_Add: return left + right;
        case TK_Sub: return left - right;
        case TK_Mul: return left * right;
        case TK_Div: return left / right;
        default: invalid_codepath;
      }
    }break;
    default: invalid_codepath;
  }
  return 0;
}

#define TEST_PARSER()    \
Set_Scratch();         \
Parse_Ctx ctx = {};    \
ctx.init();            \
Set_Ctx(&ctx, Parse_Ctx_ID)

function void
test_parse_expr(){
  TEST_PARSER();
  struct Test{String str;S64 val;};
  Array<Test> exprs = {};
  exprs.add({"(4+5)*2"_s, (4+5)*2});
  exprs.add({"4+5*2"_s, 4+5*2});
  exprs.add({"4*5+5"_s, 4*5+5});
  exprs.add({"4+5+5+3"_s, 4+5+5+3});
  
  For(exprs,it,i){
    lex_restream(&ctx, it->str, "test_expr"_s);
    Ast_Expr *result = parse_expr();
    S64 val = expr_eval(result);
    assert(val == it->val);
  }
}

//-----------------------------------------------------------------------------
// Parsing declarations
//-----------------------------------------------------------------------------
function Ast_Decl *
parse_decl(){ 
  Ast_Decl *result = 0;
  Token *token = token_match(TK_Identifier);
  if(token){
    if(token_match(TK_DoubleColon)){
      if(token_match_keyword(keyword_const)){
        Ast_Expr *expr = parse_expr();
        result = ast_decl_const(token, token->intern_val, expr);
      }
    }
    else parsing_error(token, "Encountered unexpected token while parsing a top level declarations");
  }
  return result;
}

function void
test_parse_decl(){
  TEST_PARSER();
  lex_restream(&ctx, "thing :: const 24252\n"_s, "test_parse_decl"_s);
  Ast_Decl *result = parse_decl();
}