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#lang brag
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b-program : [b-line] (/NEWLINE [b-line])* | b-statement /NEWLINE
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b-line : b-line-num [b-statement] (/":" [b-statement])* [b-rem]
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@b-line-num : INTEGER
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b-rem : REM
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@b-statement : b-end | b-print | b-goto
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| b-let | b-input | b-if
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| b-gosub | b-return | b-for | b-next
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| b-def | b-require
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b-end : /"end"
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b-print : /"print" [b-printable] (/";" [b-printable])*
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@b-printable : STRING | b-expr
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b-goto : /"goto" b-expr
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b-let : [/"let"] b-id /"=" (STRING | b-expr)
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b-if : /"if" b-expr /"then" (b-statement | b-expr)
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[/"else" (b-statement | b-expr)]
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b-input : /"input" b-id
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@b-id : ID
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b-gosub : /"gosub" b-expr
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b-return : /"return"
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b-for : /"for" b-id /"=" b-expr /"to" b-expr [/"step" b-expr]
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b-next : /"next" b-id
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b-def : /"def" b-id /"(" b-var-list /")" /"=" b-expr
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@b-var-list : ID [/"," ID]*
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b-require : /"require" b-require-spec
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@b-require-spec : ID | STRING
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b-expr : b-or-expr
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b-or-expr : [b-or-expr "or"] b-and-expr
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b-and-expr : [b-and-expr "and"] b-not-expr
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b-not-expr : ["not"] b-comp-expr
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b-comp-expr : [b-comp-expr ("="|"<"|">"|"<>")] b-sum
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b-sum : [b-sum ("+"|"-")] b-product
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b-product : [b-product ("*"|"/"|"mod")] b-neg
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b-neg : ["-"] b-expt
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b-expt : [b-expt ("^")] b-value
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@b-value : b-number | b-id | /"(" b-expr /")" | b-func
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b-func : ID /"(" b-input-list /")"
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@b-input-list : (ID | b-expr) [/"," (ID | b-expr)]*
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@b-number : INTEGER | DECIMAL
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b-repl : (b-statement | b-expr) (/":" [b-repl])*
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