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42 lines
894 B
Racket
42 lines
894 B
Racket
#lang brag
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basic-program : line*
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line: NUMBER statement [/":" statement]*
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statement : "def" id /"(" id /")" /"=" expr
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| "dim" id-expr [/"," id-expr]*
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| "end" | "stop"
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| "gosub" expr
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| "goto" expr
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| "on" expr ("gosub" | "goto") expr [/"," expr]*
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| "if" expr /"then" (statement | expr) [/"else" (statement | expr)]
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| "input" [print-list /";"] id [/"," id]*
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| [/"let"] id-expr "=" expr
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| "print" [print-list]
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| "return"
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| "for" id /"=" expr /"to" expr [/"step" expr]
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| "next" [id]
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print-list : expr [[";"] [print-list]]
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expr : comp-expr [("and" | "or") expr]
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comp-expr : sum [("=" | ">" | ">=" | "<" | "<=" | "<>") comp-expr]
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sum : [sum ("+" | "-")] product
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product : [product ("*" | "/")] power
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power : value [/"^" value]
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@value : maybe-negative-val
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| id-expr
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| /"(" expr /")"
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| STRING
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id-expr : id [/"(" expr [/"," expr]* /")"]
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@id : ID
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maybe-negative-val : ["-"] (id-expr | NUMBER) |