✨

documentation/plthy.tex

@@ -14,7 +14,7 @@
         \textit{program} & $\rightarrow$ & \texttt{hello} \texttt{|} \textit{statements}  \texttt{goodbye} \texttt{|} \\ \hline \hline
         \textit{statements} & $\rightarrow$ & \\ \hline
         \textit{statements} & $\rightarrow$ & \textit{statement} \texttt{|} \textit{statements} \\ \hline\hline
-        \textit{statement} & $\rightarrow$ & \\ \hline
+        \textit{statement} & $\rightarrow$ & \texttt{skip} \\ \hline
         \textit{statement} & $\rightarrow$ & \texttt{maybe} \textit{statement}\\ \hline
         \textit{statement} & $\rightarrow$ & \texttt{do} \textit{command}\\ \hline
         \textit{statement} & $\rightarrow$ & \texttt{[} \textit{statements} \texttt{]}\\ \hline
@@ -22,6 +22,7 @@
         \textit{statement} & $\rightarrow$ & \texttt{define} \textbf{function} \texttt{<} \textbf{int} \texttt{>} \texttt{as} \textit{statement} \\ \hline
         \textit{statement} & $\rightarrow$ & \texttt{return} \textit{expression} \\ \hline\hline
         \textit{command} & $\rightarrow$ & \textit{statement} \texttt{if} \textit{expression} \\ \hline
+        \textit{command} & $\rightarrow$ & \textit{statement} \texttt{if} \textit{expression} \textit{else} \textit{statement} \\ \hline
         \textit{command} & $\rightarrow$ & \textit{statement} \texttt{because} \textit{expression} \\ \hline
         \textit{command} & $\rightarrow$ & \textit{statement} \texttt{until} \textit{expression} \\ \hline
         \textit{command} & $\rightarrow$ & \textbf{builtin} \texttt{<} \textit{expressions} \texttt{>} \\ \hline

examples/guessing_game.plthy

@@ -1,10 +1,10 @@
 hello|
-set do random<1;128;> -> n|
+set do random<1;128;> -> r|
 set 0 -> guess|
-until variable guess = variable n [
+do [
     set do input<'guess: ';> -> guess|
-    do print<'too high';> if variable guess > variable n|
+    do do print<'too high';> if variable guess > variable r|
-    do print<'too low';> if variable guess < variable n|
+    do do print<'too low';> if variable guess < variable r|
-    do print<'correct!';> if variable guess = variable n|
+    do do print<'correct!';> if variable guess = variable r|
-]|
+] until variable guess = variable r|
 goodbye|

plthy

@@ -2,12 +2,13 @@
 """
 Usage:
     plthy (-h| --help)
-    plthy (-i| -c) FILE
+    plthy (-i| -c) [-p] FILE
 
 Options:
     -h --help   Print this help screen
     -i          Run the interpreter
     -c          Run the compiler
+    -p          Print the program structure
     FILE        The file to compile/interpret
 """
 from docopt import docopt
@@ -30,6 +31,9 @@ def main():
     program = parser.parse(tokens)
 
     if isinstance(program, Program):
+        if args["-p"]:
+            print(program)
+
         if args["-i"]:
             program.eval()
         else:

plthy_impl/ast_nodes.py

@@ -211,6 +211,10 @@ class Statement(BaseBox):
     def __repr__(self) -> str:
         return f"statement()"
 
+class StatementSkip(Statement):
+    def __repr__(self) -> str:
+        return f"skip()"
+
 class StatementSet(Statement):
     def __init__(self, expression: Exp, variable: str):
         self.expression = expression
@@ -316,6 +320,22 @@ class CommandIf(Command):
         else:
             return vtable, ftable, result
 
+class CommandIfElse(Command):
+    def __init__(self, statement: Statement, else_statement: Statement, condition):
+        self.statement = statement
+        self.else_statement = else_statement
+        self.condition = condition
+
+    def __repr__(self) -> str:
+        return f"ifelse({self.statement}, {self.condition}, {self.else_statement})"
+
+    def eval(self, vtable, ftable):
+        vtable, ftable, result = self.condition.eval(vtable, ftable)
+        if result:
+            return self.statement.eval(vtable, ftable)
+        else:
+            return self.else_statement.eval(vtable, ftable)
+
 class CommandBecause(Command):
     def __init__(self, statement: Statement, condition):
         self.statement = statement

plthy_impl/lexer.py

@@ -16,7 +16,9 @@ KEYWORD_TOKENS = [("KEYWORD_"+i.upper(), i) for i in [
     "variable",
     "return",
     "argument",
-    "set"
+    "set",
+    "skip",
+    "else"
 ]]
 
 BUILTIN_TOKENS = [("BUILTIN", i) for i in [

plthy_impl/parser.py

@@ -33,6 +33,10 @@ class Parser():
             return [tokens[0]] + tokens[2]
 
         ## statement ##
+        @self.pg.production('statement : KEYWORD_SKIP')
+        def statement_skip(tokens):
+            return ast_nodes.StatementSkip()
+
         @self.pg.production('statement : KEYWORD_SET expression SYMBOL_SET ID')
         def statement_set(tokens):
             return ast_nodes.StatementSet(tokens[1], tokens[3].value)
@@ -70,6 +74,10 @@ class Parser():
         def command_if(tokens):
             return ast_nodes.CommandIf(tokens[0], tokens[2])
 
+        @self.pg.production('command : statement KEYWORD_ELSE statement KEYWORD_IF expression')
+        def command_ifelse(tokens):
+            return ast_nodes.CommandIfElse(tokens[0],tokens[2],tokens[4])
+
         @self.pg.production('command : statement KEYWORD_BECAUSE expression')
         def command_because(tokens):
             return ast_nodes.CommandBecause(tokens[0], tokens[2])

tests/17_skip.plthy

@@ -0,0 +1,3 @@
+hello|
+skip|
+goodbye|

tests/18_if-else.expected

@@ -0,0 +1 @@
+2

tests/18_if-else.plthy

@@ -0,0 +1,3 @@
+hello|
+do do do print<1;> else do print<3;> if 1=1 else do print<2;> if 1=2|
+goodbye|