Analysis of problems with amotoen

Question

I am trying to write a grammar for parsing a simple language to describe drum loops using Clojure and amotoen . The language looks like this: -

# Test Loop # this is a comment BPM: 100 Samples: BD: bd.wav SD: sd.wav CHH: chh.wav CSH: csh.wav Body: BD: /---/---/---/--- SD: ---/--/--/-/--/- CHH: --/---/---/---/- CSH: /--------------- # this is another comment 

I defined the grammar as follows: -

 (def g { :Whitespace '(| \space \newline \tab \, :Comment) :_* '(* :Whitespace) :_ [:Whitespace '(* :Whitespace)] :Comment [\# '(* (% \newline)) \newline] :BPM [\B \P \M \: :_* '(* :Number) \newline] :Number '(* :Digit) :Digit (a/lpegs '| "0123456789") :Samples [\S \a \m \p \l \e \s \: \newline '(* :SampleDef)] :SampleDef [:_* :Name \: :_* :File \newline] :Name '(* (% \:)) :File '(* (% \newline)) :Body [\B \o \d \y \: \newline '(* :Pattern)] :Pattern [:_* :Name \: :_* '(* (| \/ \-)) '(| \newline \$)] :Document [:_* :BPM :_* :Samples :_* :Body :_* \$] }) 

When I call pegasus for each part of the sample file separately, they are processed correctly. For instance: -

 (pprint (a/pegasus :Body g (a/wrap-string "Body:\n BD: /---/---/---/---\n SD: ---/--/--/-/--/-\n CHH: --/---/---/---/-\n CSH: /---------------\n"))) 

However, when I call (pprint (a/pegasus :Document g (a/wrap-string (slurp "sample.orc")))) , all I get is nil . Similarly, if I replaced (a/wrap-string (slurp "sample.orc")) with a string containing the text contained in sample.orc .

So my question is: can anyone determine what happened to my grammar? I have all of the ideas, and I looked at him for several days. I'm sure this is something awkwardly simple, but I just don't see it!

Thanks in advance.

Answer 1

Rule :Samples consumes :Body :File may be empty, and the end of the input should be marked :$ not \$ . Here is the corrected grammar:

 (def g { :Whitespace '(| \space \tab \, :Comment) :n* '(* (| \newline :Comment)) :_* '(* :Whitespace) :_ [:Whitespace '(* :Whitespace)] :Comment [\# '(* (% \newline)) \newline] :BPM [\B \P \M \: :_* '(* :Number) \newline] :Number '(* :Digit) :Digit (a/lpegs '| "0123456789") :Samples [\S \a \m \p \l \e \s \: \newline '(* :SampleDef)] :SampleDef [:_* :Name \: :_* :File \newline] :Name '[(% \:) (* (% \:))] :File '[(% \newline) (* (% \newline))] :Body [\B \o \d \y \: \newline '(* :Pattern)] :Pattern [:_* :Name \: :_* '(* (| \/ \-)) '(| \newline :$)] :Document [:n* :BPM :n* :Samples :n* :Body :n* :$] }) ;; sample.orc contains the example input from the question text (pprint (a/pegasus :Document g (a/wrap-string (slurp "sample.orc")))) ;; output: {:Document [{:n* ({:Comment [\# (\space \T \e \s \t \space \L \o \o \p) \newline]} {:Comment [\# (\space \t \h \i \s \space \i \s \space \a \space \c \o \m \m \e \n \t) \newline]} \newline)} {:BPM [\B \P \M \: {:_* {:Whitespace \space}} {:Number ({:Digit \1} {:Digit \0} {:Digit \0})} \newline]} {:n* \newline} {:Samples [\S \a \m \p \l \e \s \: \newline ({:SampleDef [{:_* {:Whitespace \space}} {:Name [\B \D]} \: {:_* {:Whitespace \space}} {:File [\b (\d \. \w \a \v)]} \newline]} {:SampleDef [{:_* {:Whitespace \space}} {:Name [\S \D]} \: {:_* {:Whitespace \space}} {:File [\s (\d \. \w \a \v)]} \newline]} {:SampleDef [{:_* ()} {:Name [\C (\H \H)]} \: {:_* {:Whitespace \space}} {:File [\c (\h \h \. \w \a \v)]} \newline]} {:SampleDef [{:_* ()} {:Name [\C (\S \H)]} \: {:_* {:Whitespace \space}} {:File [\c (\s \h \. \w \a \v)]} \newline]})]} {:n* \newline} {:Body [\B \o \d \y \: \newline ({:Pattern [{:_* {:Whitespace \space}} {:Name [\B \D]} \: {:_* {:Whitespace \space}} (\/ \- \- \- \/ \- \- \- \/ \- \- \- \/ \- \- \-) \newline]} {:Pattern [{:_* {:Whitespace \space}} {:Name [\S \D]} \: {:_* {:Whitespace \space}} (\- \- \- \/ \- \- \/ \- \- \/ \- \/ \- \- \/ \-) \newline]} {:Pattern [{:_* ()} {:Name [\C (\H \H)]} \: {:_* {:Whitespace \space}} (\- \- \/ \- \- \- \/ \- \- \- \/ \- \- \- \/ \-) \newline]} {:Pattern [{:_* ()} {:Name [\C (\S \H)]} \: {:_* {:Whitespace \space}} (\/ \- \- \- \- \- \- \- \- \- \- \- \- \- \- \-) \newline]})]} {:n* (\newline {:Comment [\# (\space \t \h \i \s \space \i \s \space \a \n \o \t \h \e \r \space \c \o \m \m \e \n \t) \newline]})} :$]}