From 3b01fbca464b38fb39cdc5f7539f1e1390c3c753 Mon Sep 17 00:00:00 2001
From: Nathan McCarty <thatonelutenist@stranger.systems>
Date: Sat, 25 Jan 2025 00:00:52 -0500
Subject: [PATCH] numbers: Double Parser

---
 src/Parser/Numbers.md | 111 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)

diff --git a/src/Parser/Numbers.md b/src/Parser/Numbers.md
index d25343b..1f65bb5 100644
--- a/src/Parser/Numbers.md
+++ b/src/Parser/Numbers.md
@@ -93,6 +93,63 @@ integerBase10 : Parser Integer
 integerBase10 = integer base10
 ```
 
+### Double
+
+```idris
+export
+double : Base -> Parser Double
+double b = do
+  starting_state <- save
+  integer <- integer
+  fraction <- tryMaybe fraction
+  exponent <- tryMaybe exponent
+  let str = case (fraction, exponent) of
+       (Nothing, Nothing) => 
+         integer
+       (Nothing, (Just exponent)) => 
+         "\{integer}e\{exponent}"
+       ((Just fraction), Nothing) => 
+         "\{integer}.\{fraction}"
+       ((Just fraction), (Just exponent)) => 
+         "\{integer}.\{fraction}e\{exponent}"
+  Just out <- pure $ parseDouble str
+    | _ => 
+      throw $ MkParseError starting_state "Std failed to parse as double: \{str}"
+  pure out
+  where
+    parseDigit : Parser Char
+    parseDigit = do
+      GotChar char <- parseChar (hasDigit b) id
+        | GotError e => throwParseError "\{show e} is not a digit"
+        | EndOfInput => throwParseError "End Of Input"
+      pure char
+    integer : Parser String
+    integer = do
+      sign <- tryMaybe $ parseExactChar '-'
+      error <- replaceError "Expected digit"
+      digits <- map forget $ atLeastOne error parseDigit
+      case sign of
+        Nothing => pure $ pack digits
+        Just x => pure $ pack (x :: digits)
+    fraction : Parser String
+    fraction = do
+      decimal <- parseExactChar '.'
+      error <- replaceError "Expected digit"
+      digits <- map forget $ atLeastOne error parseDigit
+      pure $ pack digits
+    exponent : Parser String
+    exponent = do
+      e <- parseTheseChars ['e', 'E']
+      sign <- parseTheseChars ['+', '-']
+      error <- replaceError "Expected digit"
+      digits <- map forget $ atLeastOne error parseDigit
+      pure . pack $ sign :: digits
+
+export
+doubleBase10 : Parser Double
+doubleBase10 = double base10
+```
+
 ## Unit tests
 
 Test roundtripping a value through the provided parser
@@ -147,3 +204,57 @@ integerRoundTrip = pure $
   && !(roundtrip (-1234567890000) integerBase10) 
   && !(roundtrip (-12345678901234567890) integerBase10) 
 ```
+
+Compare our parsing of a double to the standard library's
+
+```idris
+compareDouble : String -> IO Bool
+compareDouble string = do
+  Just state <- newInternalIO string
+    | _ => do
+      putStrLn "Failed to produce parser for \{string}"
+      pure False
+  Right result <- 
+    runEff (rundownFirst doubleBase10) [handleParserStateIO state] {m = IO}
+    | Left err => do
+      printLn err
+      pure False
+  putStrLn "Input: \{string} Output: \{show result}"
+  Just double' <- pure $ parseDouble string
+    | _ => do
+      printLn "Std failed to parse as double: \{string}"
+      pure False
+  pure $ result == double'
+```
+
+```idris
+-- @@test Double Std Comparison 
+doubleRoundTrip : IO Bool
+doubleRoundTrip = pure $ 
+  !(compareDouble "0") 
+  && !(compareDouble "1") 
+  && !(compareDouble "100") 
+  && !(compareDouble "1234") 
+  && !(compareDouble "1234567890") 
+  && !(compareDouble "1234567890000") 
+  && !(compareDouble "12345678901234567890") 
+  && !(compareDouble "-1") 
+  && !(compareDouble "-100") 
+  && !(compareDouble "-1234") 
+  && !(compareDouble "-1234567890") 
+  && !(compareDouble "-1234567890000") 
+  && !(compareDouble "-12345678901234567890") 
+  && !(compareDouble "0.0") 
+  && !(compareDouble "1.0") 
+  && !(compareDouble "-1.0") 
+  && !(compareDouble "-0.0") 
+  && !(compareDouble "-0.0") 
+  && !(compareDouble "0.1234") 
+  && !(compareDouble "0.01234") 
+  && !(compareDouble "-0.1234") 
+  && !(compareDouble "-0.01234") 
+  && !(compareDouble "1.234e+5") 
+  && !(compareDouble "1.234e-5") 
+  && !(compareDouble "-1.234e+5") 
+  && !(compareDouble "-1.234e-5") 
+```