[h_sakurai]

eval(I,I):-integer(I).

eval(E1+E2,I):- eval(E1,I1),eval(E2,I2), I is I1+I2.

eval(E1E2,I):- eval(E1,I1),eval(E2,I2), I is I1I2.

:- eval(12+34,R),writeln(R),R=14.

:- halt.

Very simple Operational Semantics.

this mean

syntax

e ::= i | e+e | e * e

evaluation rule

-------------- (E-Int)

i1-->i1

e1-->i1 e2-->i2

i is i1+i2

------------------- (E-Plus)

e1+e2 --> i

e1-->i1 e2-->i2

i is i1i2

------------------- (E-Times)

e1*e2 --> i