refactor: enable Python when grammar has 4 sections

This is in anticipation of a new hybrid Java/Python mode
in which the parser runs in Java and the semantics rep-loop
runs in Python.

In this commit, when an optional 4th section is detected,
plcc.py generates ParseJsonAst.json. Thus allowing the
parser to to generate JSON ASTs when the `--json_ast`
flag is passed. It also generates experimental Python files.

---

Closes #95

Co-authored-by: Reed Everis <[email protected]>
Co-authored-by: Akshar Patel <[email protected]>
Co-authored-by: Stoney Jackson <[email protected]>

.gitignore

@@ -4,6 +4,9 @@ languages/
 # PLCC places generated Java files in directories named Java. Ignore them.
 Java/
 
+# PLCC places generated Python files in directories named Python. Ignore them.
+Python/
+
 # Created by Docker environment
 .bash_history
 

src/langs/java.py

@@ -0,0 +1,65 @@
+spec = {
+    "abstractStubFormatString" : """\
+//{base}:top//
+//{base}:import//
+import java.util.*;
+
+public abstract class {base}{ext} /*{base}:class*/ {{
+
+    public static final String $className = "{base}";
+    public static {base} parse(Scan scn$, Trace trace$) {{
+        Token t$ = scn$.cur();
+        Token.Match match$ = t$.match;
+        switch(match$) {{
+{cases}
+        default:
+            throw new PLCCException(
+                "Parse error",
+                "{base} cannot begin with " + t$.errString()
+            );
+        }}
+    }}
+
+//{base}//
+}}
+""",
+
+    "stubFormatString" : """\
+//{cls}:top//
+//{cls}:import//
+import java.util.*;
+
+// {ruleString}
+public class {cls}{ext} /*{cls}:class*/ {{
+
+    public static final String $className = "{cls}";
+    public static final String $ruleString =
+        "{ruleString}";
+
+{decls}
+
+    public {cls}({params}) {{
+//{cls}:init//
+{inits}
+    }}
+
+    public static {cls} parse(Scan scn$, Trace trace$) {{
+        if (trace$ != null)
+            trace$ = trace$.nonterm("{lhs}", scn$.lno);
+{parse}
+    }}
+
+//{cls}//
+}}
+""",
+    "extendFormatString" : ' extends {cls}',
+    "declFormatString" : 'public {fieldType} {field};',
+    "initFormatString" : 'this.{field} = {field};',
+    "paramFormatString" : '{fieldType} {field}',
+    "semFlag" : 'semantics',
+    "lineComment" : '//',
+    "blockCommentStart" : "/*",
+    "blockCommentEnd" : "*/",
+    "destFlag" : 'destdir',
+    "fileExt" : '.java'
+}

src/langs/python.py

@@ -0,0 +1,40 @@
+spec = {
+    "abstractStubFormatString" : """\
+#{base}:top#
+#{base}:import#
+
+class {base}({ext}): #{base}:class#
+
+    className = "{base}"
+
+    #{base}#
+""",
+
+    "stubFormatString" : """\
+#{cls}:top#
+#{cls}:import#
+
+# {ruleString}
+class {cls}({ext}): #{cls}:class#
+
+    className = "{cls}"
+    ruleString = "{ruleString}"
+{decls}
+
+    def __init__({params}):
+        #{cls}:init#
+{inits}
+
+#{cls}#
+""",
+    "extendFormatString" : '{cls}',
+    "declFormatString" : '{field} = None',
+    "initFormatString" : 'self.{field} = {field}',
+    "paramFormatString" : '{field}',
+    "semFlag" : 'python_semantics',
+    "lineComment" : '#',
+    "blockCommentStart" : "'''",
+    "blockCommentEnd" : "'''",
+    "destFlag" : 'python_destdir',
+    "fileExt" : '.py'
+}