Allow starting a number with a decimal point

Fixes #221.
sharkdp · May 13, 2022 · c774ab5 · c774ab5
1 parent 4a15f17
commit c774ab5
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Showing 2 changed files with 15 additions and 6 deletions.
diff --git a/src/Insect/Parser.purs b/src/Insect/Parser.purs
@@ -89,10 +89,10 @@ whiteSpace = token.whiteSpace
 -- | Parse a number.
 number ∷ P Decimal
 number = do
-  intPart ← digits
-
-  mFracPart ← optionMaybe (append <$> string "." <*> digits)
-  let fracPart = fromMaybe "" mFracPart
+  decimalPart ← fractionalPart <|> do
+    intPart ← digits
+    mFracPart ← optionMaybe fractionalPart
+    pure (intPart <> fromMaybe "" mFracPart)
 
   mExpPart ← optionMaybe $ try do
     _ ← string "e"
@@ -103,7 +103,7 @@ number = do
 
   whiteSpace
 
-  let floatStr = intPart <> fracPart <> expPart
+  let floatStr = decimalPart <> expPart
 
   case fromString floatStr of
     Just num →
@@ -118,6 +118,9 @@ number = do
       ds ← some $ oneOf ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'] <?> "a digit"
       pure $ fromCharArray (fromFoldable ds)
 
+    fractionalPart ∷ P String
+    fractionalPart = (<>) <$> string "." <*> digits
+
     fromCharArray = fromCodePointArray <<< map codePointFromChar
 
     signAndDigits ∷ P String

diff --git a/test/Main.purs b/test/Main.purs
@@ -110,11 +110,17 @@ main = runTest do
         , "+3.50"
         ]
 
+      allParseAs (Expression (scalar 0.2))
+        [ "0.2"
+        , "  0.2  "
+        , "+0.2 "
+        , ".2"
+        ]
+
       shouldFail "123.."
       shouldFail "0.."
       shouldFail ".0."
       shouldFail "."
-      shouldFail ".2"
 
     test "Large numbers" do
       allParseAs (Expression (scalar 1234567890000000.0))