Remove support for float literals starting with a period

Before this patch, writing .0 instead of 0.0 was allowed, as in C, C++, D,
Java, Go, Perl, Python and many other languages. This required a hack in the
form of an additional entry pointer for our scanner. We now get rid of it,
matching languages like Ada, Haskell, OCaml, Rust, Swift.

src/read.c

@@ -1431,8 +1431,10 @@ static void ReadFuncExprAbbrevSingle(ReaderState * rs, TypSymbolSet follow)
 **  all symbols up to one contained in <follow>.
 **
 **  <Literal> := <Int>
+**            |  <Float>
 **            |  'true'
 **            |  'false'
+**            |  '~'
 **            |  <Char>
 **            |  <Perm>
 **            |  <String>
@@ -1448,13 +1450,6 @@ static void ReadFuncExprAbbrevSingle(ReaderState * rs, TypSymbolSet follow)
 */
 static void ReadLiteral(ReaderState * rs, TypSymbolSet follow, Char mode)
 {
-    if (rs->s.Symbol == S_DOT) {
-        // HACK: The only way a dot could turn up here is in a floating point
-        // literal that starts with '.'. Call back to the scanner to deal
-        // with this.
-        ScanForFloatAfterDotHACK(&rs->s);
-    }
-
     switch (rs->s.Symbol) {
 
     /* <Int>                                                               */
@@ -1497,7 +1492,7 @@ static void ReadLiteral(ReaderState * rs, TypSymbolSet follow, Char mode)
         Match_(rs, S_CHAR, "character", follow);
         break;
 
-    /* string */
+    /* <String>                                                            */
     case S_STRING:
         GAP_ASSERT(rs->s.ValueObj != 0);
         TRY_IF_NO_ERROR { IntrStringExpr(&rs->intr, rs->s.ValueObj); }
@@ -1510,7 +1505,7 @@ static void ReadLiteral(ReaderState * rs, TypSymbolSet follow, Char mode)
         ReadListExpr(rs, follow);
         break;
 
-    /* <Rec>                                                               */
+    /* <Record>                                                            */
     case S_REC:
         ReadRecExpr(rs, follow);
         break;

src/scanner.c

@@ -361,10 +361,6 @@ static UInt GetIdent(ScannerState * s, Int i, Char c)
 **
 **  When 's->Value' is completely filled, then a GAP string object is
 **  created in 's->ValueObj' and all data is stored there.
-**
-**  The argument is used to signal if a decimal point was already read,
-**  or whether we are starting from scratch..
-**
 */
 static UInt AddCharToBuf(Obj * string, Char * buf, UInt bufsize, UInt pos, Char c)
 {
@@ -381,24 +377,20 @@ static UInt AddCharToValue(ScannerState * s, UInt pos, Char c)
     return AddCharToBuf(&s->ValueObj, s->Value, MAX_VALUE_LEN - 1, pos, c);
 }
 
-static UInt GetNumber(ScannerState * s, Int readDecimalPoint, Char c)
+static UInt GetNumber(ScannerState * s, Char c)
 {
   UInt symbol = S_ILLEGAL;
   UInt i = 0;
-  UInt seenADigit = 0;
   UInt seenExp = 0;
   UInt seenExpDigit = 0;
 
   s->ValueObj = 0;
 
-  if (readDecimalPoint) {
-    s->Value[i++] = '.';
-  }
-  else {
+  GAP_ASSERT(IsDigit(c));
+
     // read initial sequence of digits into 'Value'
     while (IsDigit(c)) {
       i = AddCharToValue(s, i, c);
-      seenADigit = 1;
       c = GET_NEXT_CHAR();
     }
 
@@ -448,21 +440,15 @@ static UInt GetNumber(ScannerState * s, Int readDecimalPoint, Char c)
       symbol = S_INT;
       goto finish;
     }
-  }
 
 
-  // When we get here we have read possibly some digits, a . and possibly
-  // some more digits, but not an e,E,d,D,q or Q
+  // When we get here we have read some digits and a dot
 
-    // read digits
+    // read digits after dot
     while (IsDigit(c)) {
       i = AddCharToValue(s, i, c);
-      seenADigit = 1;
       c = GET_NEXT_CHAR();
     }
-    if (!seenADigit)
-      SyntaxError(s, "Badly formed number: need a digit before or after the "
-                  "decimal point");
     if (c == '\\')
       SyntaxError(s, "Badly formed number");
 
@@ -502,9 +488,6 @@ static UInt GetNumber(ScannerState * s, Int readDecimalPoint, Char c)
     // If the next thing is the start of the exponential notation, read it now.
 
     if (IsAlpha(c)) {
-      if (!seenADigit)
-        SyntaxError(s, "Badly formed number: need a digit before or after "
-                    "the decimal point");
       seenExp = 1;
       i = AddCharToValue(s, i, c);
       c = GET_NEXT_CHAR();
@@ -517,9 +500,6 @@ static UInt GetNumber(ScannerState * s, Int readDecimalPoint, Char c)
     // Either we saw an exponent indicator, or we hit end of token deal with
     // the end of token case
     if (!seenExp) {
-      if (!seenADigit)
-        SyntaxError(s, "Badly formed number: need a digit before or after "
-                    "the decimal point");
       // Might be a conversion marker
       if (IsAlpha(c) && c != 'e' && c != 'E' && c != 'd' && c != 'D' &&
           c != 'q' && c != 'Q') {
@@ -593,17 +573,6 @@ static UInt GetNumber(ScannerState * s, Int readDecimalPoint, Char c)
 }
 
 
-/****************************************************************************
-**
-*F  ScanForFloatAfterDotHACK()
-**
-*/
-void ScanForFloatAfterDotHACK(ScannerState * s)
-{
-    s->Symbol = GetNumber(s, 1, PEEK_CURR_CHAR());
-}
-
-
 /****************************************************************************
 **
 *F  GetOctalDigits()
@@ -1032,7 +1001,7 @@ static UInt NextSymbol(ScannerState * s)
 
     case '0': case '1': case '2': case '3': case '4':
     case '5': case '6': case '7': case '8': case '9':
-                      return GetNumber(s, 0, c);
+                      return GetNumber(s, c);
 
     case '\377':      symbol = S_EOF;  FlushRestOfInputLine(); break;
 

src/scanner.h

@@ -361,17 +361,4 @@ void Match(ScannerState * s,
            TypSymbolSet   skipto);
 
 
-/****************************************************************************
-**
-*F  ScanForFloatAfterDotHACK()
-**
-**  This function is called by 'ReadLiteral' if it encounters a single dot in
-**  form the of the symbol 'S_DOT'. The only legal way this could happen is
-**  if the dot is the start of a float literal like '.123'. As the scanner
-**  cannot detect this without being context aware, we must provide this
-**  function to allow the reader to signal to the scanner about this.
-*/
-void ScanForFloatAfterDotHACK(ScannerState * s);
-
-
 #endif // GAP_SCANNER_H

tst/testbugfix/2013-08-21-t00295.tst

@@ -1,7 +1,6 @@
 # 2013/08/21 (MH)
 gap> . . . .
-Syntax error: Badly formed number: need a digit before or after the decimal po\
-int in stream:1
+Syntax error: literal expected in stream:1
 . . . .
 ^
-Syntax error: Record component name expected in stream:2
+Syntax error: ; expected in stream:2

tst/testinstall/float.tst

@@ -775,7 +775,7 @@ gap> ComplexConjugate(1.3);
 #
 gap> Display(1.3);
 1.3
-gap> Display(-.4e6);
+gap> Display(-0.4e6);
 -400000.
 gap> PrintObj(1.3); Print("Q\n");
 1.3Q

tst/testinstall/longnumber.tst

@@ -152,40 +152,35 @@ gap> 1.;
 1.
 gap> 0.;
 0.
-gap> .1;
-0.1
 gap> 0.1;
 0.1
 gap> 1111111111111111111111111111111111111.1;
 1.11111e+36
 gap> 1.11111111111111111111111111111111111111;
 1.11111
 gap> .;
-Syntax error: Badly formed number: need a digit before or after the decimal po\
-int in stream:1
+Syntax error: literal expected in stream:1
 .;
 ^
 gap> .n;
-Syntax error: Badly formed number: need a digit before or after the decimal po\
-int in stream:1
+Syntax error: literal expected in stream:1
 .n;
 ^
 gap> .q;
-Syntax error: Badly formed number: need a digit before or after the decimal po\
-int in stream:1
+Syntax error: literal expected in stream:1
 .q;
 ^
 gap> .0n;
-Error, failed to convert float literal
+Syntax error: literal expected in stream:1
+.0n;
+^
 gap> .0q;
-Syntax error: Badly formed number: need at least one digit in the exponent in \
-stream:1
+Syntax error: literal expected in stream:1
 .0q;
-^^^
+^
 gap> .0qn;
-Syntax error: Badly formed number: need at least one digit in the exponent in \
-stream:1
+Syntax error: literal expected in stream:1
 .0qn;
-^^^
+^
 gap> Unbind(x);
 gap> STOP_TEST( "longnumber.tst", 1);