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S-expression (sexp) parser

EvanShultz

Has anyone written an s-expression parser in SKILL and would like to share it? I found https://community.cadence.com/cadence_technology_forums/f/custom-ic-skill/29018/skill-api-to-read-sexp-file/1333078 and https://community.cadence.com/cadence_technology_forums/f/custom-ic-skill/23546/read-next-line-if-first-charcter-is-semicolon/1314699 on this topic, but nothing that was ready-to-go. And I'm sure it would be easier for me if there was reliable, tested code rather than what I would come up with. :)

Using the simple example file in the first link above I am able to read in the given file without any issues. But that is a simple example and I would like to support a more complicated input file like what is shown at https://rosettacode.org/wiki/S-Expressions. For example:

(
(data "quoted data" 123 4.5)
(data (123 (4.5) "(more" "data)"))
)

Parents

  • Oops. The example above wasn't the one that gave me trouble. This is the next step which gave me issues:

    (root test (property Blue) (attribute 7F6GJ4N7)
    (name value)
    (data "quoted data" 123 4.5 (children Alice Bob (grandchildren Jack Jill)))
    (data (123 (4.5) "(more" "data)"))
    )

    The error is:

    SYNTAX ERROR found at line 0 column XX of file XXXXXXXXXXXXXXXXXXXXXX

    *Error* lineread/read: syntax error encountered in input

    Interestingly, I noticed if I removed the leading number from attribute, making it "F6GJ4N7", then I was able to read in the file. Not sure what is the issue there.

    But even then, what is the best way to access elements? I found that using "->", at least as I expected, doesn't work. Probably I'm doing something wrong.

Reply

  • Oops. The example above wasn't the one that gave me trouble. This is the next step which gave me issues:

    (root test (property Blue) (attribute 7F6GJ4N7)
    (name value)
    (data "quoted data" 123 4.5 (children Alice Bob (grandchildren Jack Jill)))
    (data (123 (4.5) "(more" "data)"))
    )

    The error is:

    SYNTAX ERROR found at line 0 column XX of file XXXXXXXXXXXXXXXXXXXXXX

    *Error* lineread/read: syntax error encountered in input

    Interestingly, I noticed if I removed the leading number from attribute, making it "F6GJ4N7", then I was able to read in the file. Not sure what is the issue there.

    But even then, what is the best way to access elements? I found that using "->", at least as I expected, doesn't work. Probably I'm doing something wrong.

Children
  • in reply to EvanShultz

    I think the issue with (attribute 7F6GJ4N7) is that the value is being read as a symbol. Symbols cannot start with a digit, so the value should be between quotes. 

    For the second issue: if a list list contains a symbol as first element (nil, t or any other) and each successive pair starts with a symbol, you can access the elements with ->.

    For example:

    a = list( nil 'field1 "this is the first field" 'field2 "this is the second field")

    a->?  should return:

    field1

    field2

    so a->field1 contains "this is the first field".

    Bram

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