Added protection against null pointer exceptions in numeric properties.

.gitignore

@@ -9,3 +9,5 @@ pom.xml
 .nrepl-port
 
 doc/scratch.clj
+
+src/mw_parser/scratch.clj

README.md

@@ -13,15 +13,49 @@ You can see MicroWorld in action [here](http://www.journeyman.cc/microworld/) -
 but please don't be mean to my poor little server. If you want to run big maps
 or complex rule-sets, please run it on your own machines.
 
+### Version compatibility
+
+There are substantial changes in how rule functions are evaluated between 0.1.x
+versions of MicroWorld libraries and 0.3.x versions. In particular, in 0.3.x
+metadata is held on rule functions which is essential to the functioning of the
+engine. Consequently, you cannot mix 0.1.x and 0.3.x libraries: it will not work.
+
+In particular the parser in actual use has changed in 0.3.x from the
+`mw-parser.core` parser to the `mw-parser.declarative` parser. The API of the
+parser is also substantially revised and is not backwards compatible, so if
+you have code written to use 0.1.x versions of this library it will need to be
+modified. I apologise for this. On the upside, the new parser API is much
+simpler.
+
 ## Usage
 
-Main entry point is (parse-rule _string_), where string takes a form detailed
-in __[grammar](#grammar)__, below. If the rule is interpretted correctly the result will
-be the source code of a Clojure anonymous function; if the rule cannot be interpretted,
-an error 'I did not understand...' will be shown.
+Main entry point is (compile _string_), where string takes a form detailed
+in __[grammar](#grammar)__, below. If the rules represnted by the string are
+interpretted correctly, the result will be a a list of compiled Clojure
+anonymous functions; if the rule cannot be interpretted, an error 'I did not
+understand...' will be thrown.
 
-The function (compile-rule _string_) is like parse-rule, except that it returns
-a compiled Clojure anonymous function.
+Each of these functions will have metadata including:
+
+* `:rule-type` : the type of rule the function represents;
+* `:lisp` : the lisp source from which the function was compiled;
+* `:parse` : the parse-tree from which that lisp source was derived;
+* `:source` : the rule source from which the parse-tree was derived;
+* `:line : the one-based line number of the rule source in the source file.
+
+The values of `:rule-type` currently supported are:
+
+* `:production` : an if-then rule which transforms the properties of a single
+  cell, based on the values of properties of that cell and optionally of its
+  neighbours;
+* `:flow` : a flow rule which creates flows of values of a numeric property
+  from one cell to other cells.
+
+Values which it is intended will be supported include rules to create graphs
+which will enable the user to aggregate and interpret what is happening in
+the world. Types which it is envisaged will be supported include
+`:time-series`, `bar-graph` and perhaps others, but grammar for these has not
+yet been developed.
 
 ### Generated function and evaluation environment
 

src/mw_parser/declarative.clj

@@ -32,6 +32,11 @@
 ;;;;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
+;;; TODO: Either, when I first wrote this parser, I didn't adequately read the
+;;; Instaparse documentation, or Instaparse has advanced considerably since 
+;;; then. Reading the documentation now, I could probably rewrite this to
+;;; eliminate the simplify step altogether, and that would be well worth doing.
+
 (def ruleset-grammar
   "Experimental: parse a whole file in one go."
   (join "\n" ["LINES := LINE | LINE CR LINES;"

src/mw_parser/generate.clj

@@ -1,7 +1,9 @@
 (ns ^{:doc "Generate Clojure source from simplified parse trees."
       :author "Simon Brooke"}
- mw-parser.generate
-  (:require [mw-parser.utils :refer [assert-type search-tree TODO]]))
+ mw-parser.generate 
+  (:require 
+   [mw-engine.utils :refer :all] ;; may need these when macro-expanding rules.
+   [mw-parser.utils :refer [assert-type search-tree TODO]]))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;
@@ -36,7 +38,7 @@
   generate and return the appropriate rule as a function of two arguments."
   [tree]
   (assert-type tree :RULE)
-  (vary-meta 
+  (vary-meta
    ;; do macro-expansion here, because at least in theory I know what
    ;; macros are in scope here.
    (macroexpand
@@ -131,7 +133,9 @@
      (case expression-type
        :DISJUNCT-EXPRESSION (generate-disjunct-property-condition tree property qualifier expression)
        :RANGE-EXPRESSION (generate-ranged-property-condition tree property expression)
-       (list qualifier (list property 'cell) expression)))))
+       (list qualifier (if (number? expression)
+                         (list 'mw-engine.utils/get-num 'cell property)
+                         (list property 'cell)) expression)))))
 
 (defn generate-qualifier
   "From this `tree`, assumed to be a syntactically correct qualifier,
@@ -161,6 +165,21 @@
                  (generate others))
              {property expression})))))
 
+(defn trap-errors-in-dice-throw
+  "We're getting a wierd -- many would say 'impossible' -- intermittent bug
+   which appears to happen here. "
+  [sides chances action]
+  ;; (list 'try 
+        (list 'if (list '< (list 'rand sides) chances) action)
+        ;; (list 'catch 'Exception 'any
+        ;;       (list 'println (list 'format "Dice throw bug %d/%d" chances sides))
+        ;;       (list 'throw (list 'ex-info "Error in dice throw"
+        ;;                          {:total sides
+        ;;                           :chances chances
+        ;;                           :action action}
+        ;;                          'any))))
+  )
+
 (defn generate-probable-action
   "From this `tree`, assumed to be a syntactically correct probable action,
   generate and return the appropriate clojure fragment."
@@ -174,9 +193,7 @@
      total (generate (nth tree 2))
      action (generate-action (nth tree 3) others)]
     ;; TODO: could almost certainly be done better with macro syntax
-     (list 'if
-           (list '< (list 'rand total) chances)
-           action))))
+     (trap-errors-in-dice-throw total chances action))))
 
 (defn generate-action
   "From this `tree`, assumed to be a syntactically correct action,
@@ -211,10 +228,10 @@
   (assert-type tree :NUMERIC-EXPRESSION)
   (case (count tree)
     4 (let [[p operator expression] (rest tree)
-            property (if (number? p) p (list p 'cell))]
+            property (if (number? p) p (list 'mw-engine.utils/get-num 'cell p))]
         (list (generate operator) (generate property) (generate expression)))
     (case (first (second tree))
-      :SYMBOL (list (keyword (second (second tree))) 'cell)
+      :SYMBOL (list 'mw-engine.utils/get-num 'cell (generate (second tree)))
       (generate (second tree)))))
 
 (defn generate-neighbours-condition