diff --git a/topics/exercises/while3/Makefile b/topics/exercises/while3/Makefile
new file mode 100644
index 00000000..7cba8acc
--- /dev/null
+++ b/topics/exercises/while3/Makefile
@@ -0,0 +1,9 @@
+test:
+	swipl -f RunEvaluator.pro -t "main('input.txt')"
+
+debug:
+	cat input.txt
+	swipl -s RunEvaluator.pro
+
+clean:
+	rm -rf *~
diff --git a/topics/exercises/while3/Parser.pro b/topics/exercises/while3/Parser.pro
new file mode 100644
index 00000000..8e916391
--- /dev/null
+++ b/topics/exercises/while3/Parser.pro
@@ -0,0 +1,98 @@
+% Program is a list of statements
+program(S) --> statements(S).
+
+% Non-empty list
+statements(slist(H,T)) -->
+ statement(H),
+ keyword(";"),
+ statements(T).
+
+% Empty list
+statements(S) --> statement(S).
+
+% Statements
+% Skip statement
+statement(skip) -->
+ keyword("skip").
+
+% Assign statement
+statement(assign(identifier(V),E)) -->
+ identifier(V),
+ keyword(":="),
+ aexpression(E).
+
+% Conditional statement
+statement(ifthenelse(E,S1,S2)) -->
+ keyword("if"),
+ bexpression(E),
+ keyword("then"),
+ statement(S1),
+ keyword("else"),
+ statement(S2).
+
+% Expressions
+% Number is a an arithmetic expression
+aexpression(number(N)) --> number(N).
+
+% Variable reference is a an arithmetic expression
+aexpression(identifier(V)) --> identifier(V).
+
+% A sum of arithmetic expressions is also an arithmetic expression
+aexpression(add(E1,E2)) -->
+ keyword("("),
+ aexpression(E1),
+ keyword("+"),
+ aexpression(E2),
+ keyword(")").
+
+% Boolean primitives are boolean expressions
+bexpression(true) --> keyword("true").
+bexpression(false) --> keyword("false").
+
+% Comparison is a boolean expression: equality
+bexpression(equals(E1,E2)) -->
+ aexpression(E1),
+ keyword("="),
+ aexpression(E2).
+
+% Comparison is a boolean expression: less than or equal to
+bexpression(lte(E1,E2)) -->
+ aexpression(E1),
+ keyword("≤"),
+ aexpression(E2).
+
+% Dealing with spaces
+spaces --> [0' ], spaces. %'
+spaces --> [].
+
+% Keywords are space-consuming strings
+keyword(X) -->
+ spaces,
+ string(X).
+
+% Bare strings
+string([],X,X).
+string([H|T1],[H|T2],X) :- string(T1,T2,X).
+
+% Numbers are space-consuming digits
+number(N) -->
+ spaces,
+ digit(H), digits(T),
+ { number_chars(N,[H|T]) }.
+
+% Bare digits
+digits([H|T]) --> digit(H), digits(T).
+digits([]) --> [].
+digit(H,[H|T],T) :- H >= 0'0, H =< 0'9.
+
+% Identifiers are space-consuming letters
+identifier(V) -->
+ spaces,
+ letter(H), letters(T),
+ { atom_chars(V,[H|T]) }.
+
+% Bare letters
+letters([H|T]) --> letter(H), letters(T).
+letters([]) --> [].
+letter(H,[H|T],T) :- H >= 0'a, H =< 0'z.
+
diff --git a/topics/exercises/while3/RunEvaluator.pro b/topics/exercises/while3/RunEvaluator.pro
new file mode 100644
index 00000000..9c6b06e0
--- /dev/null
+++ b/topics/exercises/while3/RunEvaluator.pro
@@ -0,0 +1,19 @@
+:- ['Parser.pro','mappings.pro','compExpr.pro','bigStm.pro'].
+
+main(File) :-
+ parseFile(File,program,S),
+ write(S),nl,nl,
+ execute(S,[],M),
+ write(M),nl.
+
+parseFile(File,P,R) :-
+ open(File,read,Stream,[]), 
+ read_stream_to_codes(Stream, Contents),
+ close(Stream),
+ apply(P,[R,Contents,Rest]),
+ eof(Rest,_).
+
+eof([],[]).
+eof([0' |T],R) :- eof(T,R). %'
+eof([10|T],R) :- eof(T,R).
+
diff --git a/topics/exercises/while3/bigStm.pro b/topics/exercises/while3/bigStm.pro
index 7fdefad9..aa40bf0e 100644
--- a/topics/exercises/while3/bigStm.pro
+++ b/topics/exercises/while3/bigStm.pro
@@ -2,5 +2,22 @@
 
 execute(skip,M,M).
 
-execute(assign(X,A),M1,M2) :- evala(A,M1,Y), update(M1,X,Y,M2).
+execute(slist(S1,S2),M1,M3) :-
+ execute(S1,M1,M2),
+ execute(S2,M2,M3).
+
+execute(assign(identifier(X),A),M1,M2) :-
+ evala(A,M1,Y),
+ update(M1,X,Y,M2).
+
+execute(ifthenelse(B,S1,S2),M1,M2) :-
+ evalb(B,M1,X),
+ (
+  X == tt,
+  execute(S1,M1,M2)
+ ;
+  X == ff,
+  execute(S2,M1,M2)
+ ).
+
 
diff --git a/topics/exercises/while3/compExpr.pro b/topics/exercises/while3/compExpr.pro
index 5e98f794..8488b606 100644
--- a/topics/exercises/while3/compExpr.pro
+++ b/topics/exercises/while3/compExpr.pro
@@ -1,23 +1,59 @@
-% Evaluate Boolean expressions
+%% Evaluate arithmetic expressions
 
-evalb(true,_,tt).
+% Number is evaluated to its value
+evala(number(V),_,V).
 
-evalb(false,_,ff).
+% Variable reference is evaluated to its current value
+evala(identifier(X),M,Y) :- lookup(M,X,Y).
 
-evalb(equal(A1,A2),M,V) :-
+% Adddition
+evala(add(A1,A2),M,V) :-
   evala(A1,M,V1),
   evala(A2,M,V2),
-  equal(V1,V2,V).
+  V is V1 + V2.
 
+% Subtraction
+evala(sub(A1,A2),M,V) :-
+  evala(A1,M,V1),
+  evala(A2,M,V2),
+  V is V1 - V2.
 
-% Evaluate arithmetic expressions
+% Multiplication
+evala(mul(A1,A2),M,V) :-
+  evala(A1,M,V1),
+  evala(A2,M,V2),
+  V is V1 * V2.
 
-evala(const(V),_,V).
+%% Evaluate Boolean expressions
 
-evala(var(X),M,Y) :- lookup(M,X,Y).
+% True is tt
+evalb(true,_,tt).
 
+% False is ff
+evalb(false,_,ff).
+
+% Negation
+evalb(not(B),M,V) :-
+ evalb(B,M,V1),
+ not(V1,V).
+
+% Test for equality
+evalb(equals(A1,A2),M,V) :-
+  evala(A1,M,V1),
+  evala(A2,M,V2),
+  equals(V1,V2,V).
+
+% Test for equality
+evalb(lte(A1,A2),M,V) :-
+  evala(A1,M,V1),
+  evala(A2,M,V2),
+  lte(V1,V2,V).
 
-% Basic operations
+%% Basic operations
+equals(V1,V2,tt) :- V1 == V2.
+equals(V1,V2,ff) :- \+ V1 == V2.
+lte(V1,V2,tt) :- V1 =< V2.
+lte(V1,V2,ff) :- \+ V1 =< V2.
+not(tt,ff).
+not(ff,tt).
 
-equal(V1,V2,tt) :- V1 == V2.
-equal(V1,V2,ff) :- \+ V1 == V2.
diff --git a/topics/exercises/while3/input.txt b/topics/exercises/while3/input.txt
new file mode 100644
index 00000000..cf536f71
--- /dev/null
+++ b/topics/exercises/while3/input.txt
@@ -0,0 +1 @@
+y:=2; if y = 3 then z := y else z := 1000