Add BBC Basic lexer (#1280)

This commit adds a lexer for ARM BBC Basic. Some features of BBC BASIC
for Windows and BBC BASIC for SDL2.0 are not included.

lib/rouge/demos/bbcbasic

@@ -0,0 +1,6 @@
+REM > DefaultFilename
+REM Ordinary comment
+FOR n=1 TO 10
+PRINTTAB(n)"Hello there ";FNnumber(n)DIV3+1
+NEXT:END
+DEFFNnumber(x%)=ABS(x%-4)

lib/rouge/lexers/bbcbasic.rb

@@ -0,0 +1,112 @@
+# -*- coding: utf-8 -*- #
+# frozen_string_literal: true
+
+module Rouge
+  module Lexers
+    class BBCBASIC < RegexLexer
+      title "BBCBASIC"
+      desc "BBC BASIC syntax"
+      tag 'bbcbasic'
+      filenames '*,fd1'
+
+      def self.punctuation
+        @punctuation ||= %w(
+          [,;'~] SPC TAB
+        )
+      end
+
+      def self.function
+        @function ||= %w(
+          ABS ACS ADVAL ASC ASN ATN BEATS BEAT BGET# CHR\$ COS COUNT DEG DIM
+          EOF# ERL ERR EVAL EXP EXT# FN GET\$# GET\$ GET HIMEM INKEY\$ INKEY
+          INSTR INT LEFT\$ LEN LN LOG LOMEM MID\$ OPENIN OPENOUT OPENUP PAGE
+          POINT POS PTR# RAD REPORT\$ RIGHT\$ RND SGN SIN SQR STR\$ STRING\$ SUM
+          SUMLEN TAN TEMPO TIME\$ TIME TOP USR VAL VPOS
+        )
+      end
+
+      def self.statement
+        @statement ||= %w(
+          BEATS BPUT# CALL CASE CHAIN CLEAR CLG CLOSE# CLS COLOR COLOUR DATA
+          ELSE ENDCASE ENDIF ENDPROC ENDWHILE END ENVELOPE FOR GCOL GOSUB GOTO
+          IF INSTALL LET LIBRARY MODE NEXT OFF OF ON ORIGIN OSCI OTHERWISE
+          OVERLAY PLOT PRINT# PRINT PROC QUIT READ REPEAT REPORT RETURN SOUND
+          STEP STEREO STOP SWAP SYS THEN TINT TO VDU VOICES VOICE UNTIL WAIT
+          WHEN WHILE WIDTH
+        )
+      end
+
+      def self.operator
+        @operator ||= %w(
+          << <= <> < >= >>> >> > [-!$()*+/=?^|] AND DIV EOR MOD NOT OR
+        )
+      end
+
+      def self.constant
+        @constant ||= %w(
+          FALSE TRUE
+        )
+      end
+
+      state :expression do
+        rule %r/#{BBCBASIC.function.join('|')}/o, Name::Builtin  # function or pseudo-variable
+        rule %r/#{BBCBASIC.operator.join('|')}/o, Operator
+        rule %r/#{BBCBASIC.constant.join('|')}/o, Name::Constant
+        rule %r/"[^"]*"/o, Literal::String
+        rule %r/[a-z_`][\w`]*[$%]?/io, Name::Variable
+        rule %r/@%/o, Name::Variable
+        rule %r/[\d.]+/o, Literal::Number
+        rule %r/%[01]+/o, Literal::Number::Bin
+        rule %r/&[\h]+/o, Literal::Number::Hex
+      end
+
+      state :root do
+        rule %r/(:+)( *)(\*)(.*)/ do
+          groups Punctuation, Text, Keyword, Text # CLI command
+        end
+        rule %r/(\n+ *)(\*)(.*)/ do
+          groups Text, Keyword, Text # CLI command
+        end
+        rule %r/(ELSE|OTHERWISE|REPEAT|THEN)( *)(\*)(.*)/ do
+          groups Keyword, Text, Keyword, Text # CLI command
+        end
+        rule %r/[ \n]+/o, Text
+        rule %r/:+/o, Punctuation
+        rule %r/[\[]/o, Keyword, :assembly1
+        rule %r/REM *>.*/o, Comment::Special
+        rule %r/REM.*/o, Comment
+        rule %r/(?:#{BBCBASIC.statement.join('|')}|CIRCLE(?: *FILL)?|DEF *(?:FN|PROC)|DRAW(?: *BY)?|DIM(?!\()|ELLIPSE(?: *FILL)?|ERROR(?: *EXT)?|FILL(?: *BY)?|INPUT(?:#| *LINE)?|LINE(?: *INPUT)?|LOCAL(?: *DATA| *ERROR)?|MOUSE(?: *COLOUR| *OFF| *ON| *RECTANGLE| *STEP| *TO)?|MOVE(?: *BY)?|ON(?! *ERROR)|ON *ERROR *(?:LOCAL|OFF)?|POINT(?: *BY)?(?!\()|RECTANGE(?: *FILL)?|RESTORE(?: *DATA| *ERROR)?|TRACE(?: *CLOSE| *ENDPROC| *OFF| *STEP(?: *FN| *ON| *PROC)?| *TO)?)/o, Keyword
+        mixin :expression
+        rule %r/#{BBCBASIC.punctuation.join('|')}/o, Punctuation
+      end
+
+      # Assembly statements are parsed as
+      # {label} {directive|opcode |']' {expressions}} {comment}
+      # Technically, you don't need whitespace between opcodes and arguments,
+      # but this is rare in uncrunched source and trying to enumerate all
+      # possible opcodes here is impractical so we colour it as though
+      # the whitespace is required. Opcodes and directives can only easily be
+      # distinguished from the symbols that make up expressions by looking at
+      # their position within the statement. Similarly, ']' is treated as a
+      # keyword at the start of a statement or as punctuation elsewhere. This
+      # requires a two-state state machine.
+
+      state :assembly1 do
+        rule %r/ +/o, Text
+        rule %r/]/o, Keyword, :pop!
+        rule %r/[:\n]/o, Punctuation
+        rule %r/\.[a-z_`][\w`]*%? */io, Name::Label
+        rule %r/(?:REM|;)[^:\n]*/o, Comment
+        rule %r/[^ :\n]+/o, Keyword, :assembly2
+      end
+
+      state :assembly2 do
+        rule %r/ +/o, Text
+        rule %r/[:\n]/o, Punctuation, :pop!
+        rule %r/(?:REM|;)[^:\n]*/o, Comment, :pop!
+        mixin :expression
+        rule %r/[!#,@\[\]^{}]/, Punctuation
+      end
+    end
+  end
+end

spec/lexers/bbcbasic_spec.rb

@@ -0,0 +1,14 @@
+# -*- coding: utf-8 -*- #
+# frozen_string_literal: true
+
+describe Rouge::Lexers::BBCBASIC do
+  let(:subject) { Rouge::Lexers::BBCBASIC.new }
+
+  describe 'guessing' do
+    include Support::Guessing
+
+    it 'guesses by filename' do
+      assert_guess :filename => 'foo,fd1'
+    end
+  end
+end

spec/visual/samples/bbcbasic

@@ -0,0 +1,44 @@
+REM > DefaultFilename
+PRINT:REM Ordinary comment: This is still a comment
+ONERRORPRINTERR:END
+ERROR1,"error"
+IF2*2=4ELSE*Cat:4.$
+FOR n=1 TO 10
+PRINTTAB(n)"Hello there ";FNnumber(n)DIV3+1'INKEY$(500)INKEY(500)
+NEXT
+DIM code% 100
+FOR opt=0 TO 3 STEP 3
+P%=code%
+[OPT opt
+.label1%
+.label2% LDR r0,[P%MOD2,#0]
+ MOV pc,r14:REM comments in assembly terminate at colon:EQUD -1
+.label3;comment
+ ALIGN
+.label4
+]
+NEXT
+CALL code%:PRINT USR(code%)
+DIM`(100,100):PRINTDIM(`())
+X=&FEDCBA98:PRINT X,~X,X>>>1,X>>1,X>1
+PRINT %1010%1111:REM Prints "10" then "15"
+A%=@%:@%="F10.2":PRINT~@%:@%=A%
+ELLIPSE FILL 100,100,100,50,45
+MOUSEOFF
+DIM block% 100
+block%!2*4=0
+CASE thing OF
+WHEN 1:PRINT"one"
+OTHERWISE *echo not one
+ENDCASE
+*Help
+ON
+ONA%PROCa,PROCb ELSEPROCc
+ONERRORONERROROFF:OFF:REPORT:END
+IF A% PRINT"Problem"
+IF A$ THEN PRINT"Not a problem"
+WHILENOTEOF#f PRINTBGET#f:ENDWHILE
+REPEATUNTILFALSE
+END
+DEFPROCa PRINT"Hello world":ENDPROC
+DEFFNnumber(x%)=ABS(x%-4)