From bc7525e3531e6a83eaa400e6af642f751ca9281f Mon Sep 17 00:00:00 2001
From: Florian Schroedl <flo.schroedl@gmail.com>
Date: Sun, 28 Aug 2022 18:19:42 +0200
Subject: [PATCH] Add starOfStream function

---
 src_v2/parser/parser_api.nim   | 15 +++++++++++++++
 src_v2/parser/parser_types.nim | 10 ++++++++++
 2 files changed, 25 insertions(+)

diff --git a/src_v2/parser/parser_api.nim b/src_v2/parser/parser_api.nim
index bb7e49e..cf9d384 100644
--- a/src_v2/parser/parser_api.nim
+++ b/src_v2/parser/parser_api.nim
@@ -112,6 +112,21 @@ proc str*(expectedString: string): parserFnT {.inline.} =
       res = res.flatMap(ch(c))
     return res
 
+proc startOfStream*(parser: Parser): ParserResult =
+  ## Check if the following character is the end of the stream.
+  ## Errors when the end of stream was already reached.
+  let position = parser.state.position
+
+  if position == 0 or position == -1:
+    ok(parser)
+  else:
+    err(ParserError(
+      kind: startOfStringErr,
+      expected: "startOfStream",
+      index: position,
+      parser: parser,
+    ))
+
 proc endOfStream*(parser: Parser): ParserResult =
   ## Check if the following character is the end of the stream.
   ## Errors when the end of stream was already reached.
diff --git a/src_v2/parser/parser_types.nim b/src_v2/parser/parser_types.nim
index 4ff813c..0f968c9 100644
--- a/src_v2/parser/parser_types.nim
+++ b/src_v2/parser/parser_types.nim
@@ -36,6 +36,7 @@ type
     choiceMismatchErr
     charMismatchErr
     endOfStringErr
+    startOfStringErr
   ParserError* = ref object
     kind*: ParserErrorKind
     unexpected*: string
@@ -287,6 +288,15 @@ func `$`*(x: ParserError): string =
 {original}
 {errSpace}^ Expected 'EndOfString' at {index} but got {original.len - 1}"""
 
+    of startOfStringErr(parser: @parser, index: @index):
+      let original = parser.state.stream
+      .deleteAfterNewline(parser.state.position)
+      let errSpace = " ".repeat(max(0, index))
+
+      &"""Parsing Error (StartOFString Expected):
+{original}
+{errSpace}^ Expected 'StartOfString' at index {index}"""
+
     else: "ParseError"
 
 when isMainModule: