Add tasks for all the new languages

Task/S-Expressions/Potion/s-expressions.potion

@@ -0,0 +1,72 @@
+isdigit = (c): 47 < c ord and c ord < 58.
+iswhitespace = (c): c ord == 10 or c ord == 13 or c == " ".
+
+# str: a string of the form "...<nondigit>[{<symb>}]..."
+# i: index to start at (must be the index of <nondigit>)
+# => returns (<the symbol as a string>, <index after the last char>)
+parsesymbol = (str, i) :
+   datum = ()
+   while (str(i) != "(" and str(i) != ")" and not iswhitespace(str(i)) and str(i) != "\"") :
+      datum append(str(i++))
+   .
+   (datum join, i)
+.
+
+# str: a string of the form "...[<minus>]{<digit>}[<dot>{<digit>}]..."
+# i: index to start at (must be the index of the first token)
+# => returns (<float or int>, <index after the last digit>)
+parsenumber = (str, i) :
+   datum = ()
+   dot = false
+   while (str(i) != "(" and str(i) != ")" and not iswhitespace(str(i)) and str(i) != "\"") :
+      if (str(i) == "."): dot = true.
+      datum append(str(i++))
+   .
+   if (dot): (datum join number, i).
+   else: (datum join number integer, i).
+.
+
+# str: a string of the form "...\"....\"..."
+# i: index to start at (must be the index of the first quote)
+# => returns (<the string>, <index after the last quote>)
+parsestring = (str, i) :
+   datum = ("\"")
+   while (str(++i) != "\"") :
+      datum append(str(i))
+   .
+   datum append("\"")
+   (datum join, ++i)
+.
+
+# str: a string of the form "...(...)..."
+# i: index to start at
+# => returns (<tuple/list>, <index after the last paren>)
+parselist = (str, i) :
+   lst = ()
+   data = ()
+   while (str(i) != "("): i++.
+   i++
+   while (str(i) != ")") :
+      if (not iswhitespace(str(i))) :
+         if (isdigit(str(i)) or (str(i) == "-" and isdigit(str(i + 1)))): data = parsenumber(str, i).
+         elsif (str(i) == "\""): data = parsestring(str, i).
+         elsif (str(i) == "("): data = parselist(str, i).
+         else: data = parsesymbol(str, i).
+         lst append(data(0))
+         i = data(1)
+      . else :
+         ++i
+      .
+   .
+   (lst, ++i)
+.
+
+parsesexpr = (str) :
+   parselist(str, 0)(0)
+.
+
+parsesexpr("(define (factorial x) \"compute factorial\" (version 2.0) (apply * (range 1 x)))") string print
+"\n" print
+parsesexpr("((data \"quoted data\" 123 4.5)
+ (data (!@# (4.5) \"(more\" \"data)\")))") string print
+"\n" print