58 lines
1.6 KiB
Plaintext
58 lines
1.6 KiB
Plaintext
{
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module Lexer
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open System
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open FSharp.Text.Lexing
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open System.Text
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let keyword (s : string) =
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match s with
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| "let" -> Parser.LET
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| "in" -> Parser.IN
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| "sum" -> Parser.SUM
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| "prod" -> Parser.PROD
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| "max" -> Parser.MAX
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| "argmax" -> Parser.ARGMAX
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| "to" -> Parser.TO
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| "of" -> Parser.OF
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| _ -> Parser.VAR s
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}
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rule Token = parse
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(* Skip whitespace. *)
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[' ' '\t' '\r' '\n' ]+
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{ Token lexbuf }
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(* Integers. *)
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| '0' | ['1'-'9']['0'-'9']*
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{ Parser.INT (int (Encoding.UTF8.GetString lexbuf.Lexeme)) }
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(* Symbols *)
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| '(' { Parser.LPAR }
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| ')' { Parser.RPAR }
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| '=' { Parser.EQ }
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| '+' { Parser.PLUS }
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| '-' { Parser.MINUS }
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| '*' { Parser.TIMES }
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| ['a'-'z' 'A'-'Z']* ('_' ['a'-'z' 'A'-'Z' '_' '0'-'9']* )?
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{ keyword (Encoding.UTF8.GetString lexbuf.Lexeme) }
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(* FIXME: You should implement lexing for:
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(1) Variable names: may contain letters, digits and underscores,
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but it must start with one (or several) letters,
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and a digit must be preceeded by an underscore.
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(2) Keywords: 'let', 'in', 'sum', ...
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(3) Symbols: '=', '+', ...
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For (1) and (2), please change the regular expression above
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to be consistent with the rule defining variable names,
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and implement the keywords function.
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For (3), add the relevant regular expressions under 'Symbols'
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*)
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(* Special end of file symbol. *)
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| eof { Parser.EOF }
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(* We don't understand anything else. *)
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| _ { failwith "lexer error" }
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