quytelda/babel

Random sequence generator written in Haskell.

babel's Issues

Babel exits with failure when using -v and -h flags.

The program checks too early whether or not the user has provided a grammar file, which is not relevant or expected when asking the program for help or version information. This causes the --version and --help options to exit with an error status.

quytelda@kahja % babel --version
You must provide a grammar file.
Usage: babel [OPTION...] GRAMMAR_FILE
  -h         --help          Display help and usage information.
  -n N                       Generate N different sequences.
  -o FILE    --output=FILE   Redirect output to FILE.
  -s SYMBOL  --start=SYMBOL  Use SYMBOL as the starting symbol ("S" is the default.).
  -v         --version       Display version information.

Failure to compile with GHC < 8.0

Babel fails to build using cabal configure && cabal build1 with the error:

src/Main.hs:104:30: Not in scope: ‘<$>’

Repeated Symbols Overwrite

Issue: when a config file contains multiple lines with the same left hand side (LHS), then the last defined LHS will overwrite all previously defined rules.

How to Replicate: Create a config file with two rules for the same symbol on the LHS, then run babel with that config file. Only the second rule will be seen.

Why this is an issue: For clarity sake on long rules, or for style preference, users may wish to define rules for one symbol across multiple lines.

Semicolons End Parsing

Problem: When a semicolon is used in a config file, the rest of the config file is not read.

How to replicate: Create a config file with a semicolon somewhere in the middle, run babel with the config file. You will see that all the rules before the semi colon are used, and all the rules afterwards are not.

Why this is a problem: After the first change semi-colons are no longer a syntactically significant, so they should be available as symbols. Especially if a CFG is being constructed for say a language like structure.

CFG Files Ending with New Line Don't Work

Issue:
If a CFG file ends with a new line character, babel will fail with the error:

(line x, column 1):
unexpected end of input
expecting space

where x is 1 + the number of lines in the CFG file.

Steps to replicate:

1. Create a CFG file ending in a new line.
2. Run babel with that CFG file as the grammar file input

Reasons this is an issue:
Many common text editors automatically append a new line to text files when they are done being edited.

Potential Solutions:
Check if a line consists of just a newline character and if so skip the parsing step
Strip the newline character off the end of the file