jme.isDeterministic looks at the expression of lambda tokens

This isn't *strictly* correct: an anonymous function `a -> random(0,1)` *is* deterministic as an expression that produces a lambda token, but the output of the lambda is not deterministic.
To be really accurate, a lambda should only count as non-deterministic when it's applied, e.g. `i -> random(0,i)` is deterministic but `(i -> random(0,i))(4)` is not. But I'd have to remember that for every function that takes lambdas.

This was the easiest way of ensuring that jme.isDeterministic doesn't think that expressions using non-deterministic lambdas are deterministic, e.g. `map(i->random(i..2i), 0..3)`

Author: christianp

runtime/scripts/jme.js

@@ -931,6 +931,8 @@ var jme = Numbas.jme = /** @lends Numbas.jme */ {
                     }
                 }
                 return true;
+            case 'lambda':
+                return jme.isDeterministic(expr.tok.expr, scope);
             default:
                 if(!expr.args) {
                     return true;

tests/jme-runtime.js

@@ -9754,6 +9754,8 @@ var jme = Numbas.jme = /** @lends Numbas.jme */ {
                     }
                 }
                 return true;
+            case 'lambda':
+                return jme.isDeterministic(expr.tok.expr, scope);
             default:
                 if(!expr.args) {
                     return true;

tests/jme/jme-tests.mjs

@@ -1514,6 +1514,9 @@ Numbas.queueScript('jme_tests',['qunit','jme','jme-rules','jme-display','jme-cal
         check('"{a} then {random(1,2)}"',false);
         check('"{a} then {b}"',true);
         check('safe("these empty braces: {}")', true);
+        check('a -> 1', true);
+        check('a -> random(a,0)', false);
+        check('map(a -> random(a..2a), 0..3)', false);
 
         var scope = new jme.Scope([Numbas.jme.builtinScope]);
         var fn = new jme.funcObj('fn',[],jme.types.TNum,function() { return 1; });

tests/numbas-runtime.js

@@ -9090,6 +9090,8 @@ var jme = Numbas.jme = /** @lends Numbas.jme */ {
                     }
                 }
                 return true;
+            case 'lambda':
+                return jme.isDeterministic(expr.tok.expr, scope);
             default:
                 if(!expr.args) {
                     return true;