docs tweaks
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Joshua Bell
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@ -51,7 +51,7 @@ This is intended as a quick reference for the <a href="index.htm">Applesoft BASI
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<dl>
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<dt>CLEAR<dd>Clear all variables
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<dt>[LET] <var>var</var> = <var>expr</var><dd>Assign variable
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<dt>DIM <var>var</var>( <var>size</var> [ , <var>size2</var> ...] ) [ , <var>var2</var>( <var>size</var> [ , <var>size2</var> ...] ) ... ] <dd>Allocate array
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<dt>DIM <var>var</var>( <var>size</var> [ , <var>size2</var> ...] ) [ , <var>var2</var>( <var>size</var> [ , <var>size2</var> ...] ) ...] <dd>Allocate array(s) with given dimension(s)
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<dt>DEF FN <var>f</var>(<var>var</var> ) = <var>expr</var><dd>Define function of a single variable <a href="#def_fn_string">[1]</a>
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</dl>
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</section>
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@ -59,16 +59,16 @@ This is intended as a quick reference for the <a href="index.htm">Applesoft BASI
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<section>
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<h3>Flow Control</h3>
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<dl>
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<dt>GOTO<dd>Go to line number
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<dt>GOSUB <var>line</var><dd>Go to subroutine
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<dt>GOTO <var>line</var><dd>Jump to line number
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<dt>GOSUB <var>line</var><dd>Enter subroutine at line number
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<dt>RETURN<dd>Return from subroutine
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<dt>ON <var>expr</var> GOTO <var>line</var> [, <var>line2</var> ... ]<dd>Branch based on index (value = 1, 2, ...)
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<dt>ON <var>expr</var> GOSUB <var>line</var> [, <var>line2</var> ... ]<dd>Subroutine branch based on index (value = 1, 2, ...)
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<dt>POP<dd>Convert last gosub into a goto
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<dt>ON <var>expr</var> GOTO <var>line</var> [, <var>line2</var> ...]<dd>Branch based on index (value = 1, 2, ...)
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<dt>ON <var>expr</var> GOSUB <var>line</var> [, <var>line2</var> ...]<dd>Subroutine branch based on index (value = 1, 2, ...)
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<dt>POP<dd>Convert last <code>GOSUB</code> into a <code>GOTO</code>
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<dt>FOR <var>var</var> = <var>start</var> TO <var>end</var> [ STEP <var>incr</var> ]<dd>Loop with counter variable
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<dt>NEXT [<var>var</var> [, <var>var</var> ...] ]<dd>End of loop(s)
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<dt>IF <var>expr</var> THEN <var>statement</var><br />IF <var>expr</var> GOTO <var>line</var><dd>Conditional; if expr is false, rest of line is skipped
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<dt>END<dd>Terminate program
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<dt>IF <var>expr</var> THEN <var>statement</var><br />IF <var>expr</var> GOTO <var>line</var><dd>Conditional; if <var>expr</var> is false, rest of line is skipped
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<dt>END<dd>Terminate program cleanly
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<dt>STOP<dd>Break, as if an error occurred
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</dl>
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</section>
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@ -77,19 +77,20 @@ This is intended as a quick reference for the <a href="index.htm">Applesoft BASI
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<h3>Error Handling</h3>
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<dl>
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<dt>ONERR GOTO <var>line</var><dd>Set error hook
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<dt>RESUME<dd>Retry line that caused ONERR GOTO
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<dt>RESUME<dd>Retry line that caused <code>ONERR GOTO</code>
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</dl>
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</section>
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<section>
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<h3>Input/Output</h3>
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<dl>
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<dt>PRINT <var>expr</var> [ [;,] <var>expr2</var> ... ] [;]<dd>Output text
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<dt>INPUT [<var>string</var> ;] <var>var</var> [, <var>var2</var> ... ]<dd>Read line of input
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<dt>PRINT <var>expr</var> [ [;,] <var>expr2</var> ... ] [;]<dd>Output text. <code>;</code> concatenates,
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<code>,</code> advances to next tab stop. A trailing <code>;</code> suppresses line break.
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<dt>INPUT [<var>string</var> ;] <var>var</var> [, <var>var2</var> ...]<dd>Read line of comma-delimited input, with optional prompt
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<dt>GET <var>var</var><dd>Read single key
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<dt>HOME<dd>Clear text display
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<dt>HTAB <var>expr</var><dd>Position text cursor horizontally
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<dt>VTAB <var>expr</var><dd>Position text cursor vertically
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<dt>HTAB <var>expr</var><dd>Position text cursor horizontally (1...40 or 1...80)
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<dt>VTAB <var>expr</var><dd>Position text cursor vertically (1...24)
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<dt>INVERSE<dd>Set output mode to black-on-white
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<dt>FLASH<dd>Set output mode to flashing
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<dt>NORMAL<dd>Set output mode to white-on-black
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@ -100,7 +101,7 @@ This is intended as a quick reference for the <a href="index.htm">Applesoft BASI
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<section>
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<h3>Miscellaneous</h3>
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<dl>
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<dt>REM [ <var>comment</var> ]<dd>Begin a comment; rest of line is skipped
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<dt>REM [<var>comment</var>]<dd>Begin a comment; rest of line is skipped
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<dt>TRACE<dd>Turn on trace mode (line numbers printed)
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<dt>NOTRACE<dd>Turn off trace mode
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</dl>
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@ -109,8 +110,8 @@ This is intended as a quick reference for the <a href="index.htm">Applesoft BASI
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<section>
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<h3>Inline Data</h3>
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<dl>
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<dt>DATA <var>value</var> [, <var>value2</var> ... ]<dd>Define inline data
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<dt>READ <var>var</var> [, <var>var2</var> ... ]<dd>Read the next DATA value
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<dt>DATA <var>value</var> [, <var>value2</var> ...]<dd>Define inline data
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<dt>READ <var>var</var> [, <var>var2</var> ...]<dd>Read the next DATA value
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<dt>RESTORE<dd>Restore the DATA pointer to the first value
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</dl>
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</section>
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@ -118,7 +119,7 @@ This is intended as a quick reference for the <a href="index.htm">Applesoft BASI
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<section>
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<h3>Lo-Res Graphics</h3>
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<dl>
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<dt>GR<dd>Set display to lores mode, clear screen
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<dt>GR<dd>Set display to mixed test/low resolution ("lores") graphics mode, clear screen to black
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<dt>COLOR= <var>expr</var><dd>Set lores color (0...15)
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<dt>PLOT <var>expr</var>, <var>expr</var><dd>Plot lores point (x = 0...39, y = 0...39/47)
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<dt>HLIN <var>expr</var>, <var>expr</var> AT <var>expr</var><dd>Plot horizontal line (x1, x2 at y)
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@ -129,8 +130,8 @@ This is intended as a quick reference for the <a href="index.htm">Applesoft BASI
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<section>
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<h3>Hi-Res Graphics</h3>
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<dl>
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<dt>HGR<dd>Set display to hires mode, clear screen
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<dt>HGR2<dd>Set display to hires mode (page 2), clear screen
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<dt>HGR<dd>Set display to mixed/high resolution ("hires") graphics mode, clear screen to black
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<dt>HGR2<dd>Set display to full hires mode (page 2), clear screen
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<dt>HPLOT [TO] <var>expr</var>, <var>expr</var> [ TO <var>expr</var>, <var>expr</var> ] ... <dd>Plot hires point/line (x=0...279, y=0...191)
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<dt>HCOLOR= <var>expr</var><dd>Set hires color (0...7)
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</dl>
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@ -196,10 +197,10 @@ This is intended as a quick reference for the <a href="index.htm">Applesoft BASI
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<li><code>POKE 49200,0</code> - toggle speaker (no-op)
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<li><code>POKE 49232,0</code> - graphics mode
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<li><code>POKE 49233,0</code> - text mode
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<li><code>POKE 49234,0</code> - full graphics
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<li><code>POKE 49235,0</code> - split screen
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<li><code>POKE 49238,0</code> - lores
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<li><code>POKE 49239,0</code> - hires
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<li><code>POKE 49234,0</code> - full graphics mode
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<li><code>POKE 49235,0</code> - mixed text/graphics mode
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<li><code>POKE 49238,0</code> - lores graphics mode
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<li><code>POKE 49239,0</code> - hires graphics mode
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</ul>
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<dt>CALL <var>expr</var><dd>Call native routine
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@ -535,7 +536,8 @@ Statement = data-declaration | remark | Command | EmptyStatement
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Command = identifier /*...*/ | reserved /*...*/
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</pre>
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<p>Statements ("commands" in the above grammar) are parsed with distinct cases for each statement type.
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<p>Due to the irregular structure of the BASIC language, statements ("commands" in the above grammar)
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are parsed with distinct cases for each statement type.
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Most statements compile into a function call to a library of Applesoft routines. Expressions are parsed
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with a standard recursive descent parser. The parser generates JavaScript expressions for each expression,
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which are used as arguments for the library calls.</p>
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@ -544,23 +546,22 @@ which are used as arguments for the library calls.</p>
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Expression = OrExpression
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OrExpression = AndExpression { 'OR' AndExpression }
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AndExpression = RelationalExpression { 'AND' RelationalExpression }
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RelationalExpression = AdditiveExpression { RelOp AdditiveExpression }
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RelOp = '=' | '<' | '>' | '<=' | '=<' | '>=' | '=>' | '<>' | '><'
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RelationalExpression = AdditiveExpression { ('=' | '<' | '>' | '<=' | '=<' | '>=' | '=>' | '<>' | '><') AdditiveExpression }
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AdditiveExpression = MultiplicativeExpression { ( '+' | '-' ) MultiplicativeExpression }
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MultiplicativeExpression = PowerExpression { ( '*' | '/' ) PowerExpression }
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PowerExpression = UnaryExpression [ '^' UnaryExpression ]
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PowerExpression = UnaryExpression { '^' UnaryExpression }
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UnaryExpression = ( '+' | '-' | 'NOT' ) UnaryExpression
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| FinalExpression
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| FinalExpression
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FinalExpression = number-literal
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| string-literal
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| 'FN' user_function_name '(' Expression ')'
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| reserved '(' Expression { ',' Expression } ')'
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| identifier [ '(' Expression { ',' Expression } ')' ]
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| '(' Expression ')'
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| string-literal
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| 'FN' user_function_name '(' Expression ')'
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| reserved '(' Expression { ',' Expression } ')'
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| identifier [ '(' Expression { ',' Expression } ')' ]
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| '(' Expression ')'
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</pre>
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<p>Since Applesoft supports re-entrant error handling and synchronous input,
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the output of the compiler is an array of statement-functions plus a driver
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the output of the compiler is an array of statement-functions plus an executor
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function which implements the logic for walking over the array.<p>
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</section>
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@ -568,19 +569,21 @@ function which implements the logic for walking over the array.<p>
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<!-- ================================================== -->
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<h2>Extensions beyond Standard Applesoft</h2>
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<!-- ================================================== -->
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<ul style="list-style: none;">
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<ol>
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<li id="def_fn_string">
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[1] <code>DEF FN</code> supports string and integer functions
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<code>DEF FN</code> supports string and integer functions
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e.g. <code>DEF FN IN$(X$) = " " + X$</code>
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(but return type must still match argument type)
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- the return type must match the argument type, so string-to-number or number-to-string functions
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can not be implemented.
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<li id="eqeq">
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[2] <code>==</code> is supported for equality comparisons, in addition to <code>=</code>
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"Double equals" <code>==</code> is supported for equality comparisons, with the same meaning as "single equals" <code>=</code>
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<li id="chr_extras">
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[3] When printing characters, <code>CHR$()</code> values greater than 255 generate glyphs that might be useful for certain maze games.
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When printing characters, <code>CHR$()</code> values greater than 255 generate glyphs that might be useful for implementing certain maze games. <em>(An earlier version of this page allowed arbitrary Unicode characters to be displayed, but the text is now displayed using bitmaps so that is not possible.)</em>
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<li id="hscrn">
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[4] <code>HSCRN(<var>x</var>,<var>y</var>)</code> is added to allow reading the
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hires screen. On a real Apple this required a machine-language routine (or a shape table and <code>XDRAW</code>).
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</ul>
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<code>HSCRN(<var>x</var>,<var>y</var>)</code> is added to allow reading the
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hires screen. On a real Apple this required a machine-language routine (or a shape table and <code>XDRAW</code>) and
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extensive knowledge of the Apple's color generation scheme.
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</ol>
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</section>
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<script type="text/javascript" src="../polyfill/polyfill.js"></script>
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