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# This example Tamsin program was written by Chris Pressey, and is
# hereby placed in the public domain.  It comes with NO WARRANTY.

main = expr0 → E using scanner & eval(E).
expr0 = expr1 → E1 & {"or" & expr1 → E2 & E1 ← or(E1,E2)} & E1.
expr1 = term → E1 & {"and" & term → E2 & E1 ← and(E1,E2)} & E1.
term = "true" | "false" | "(" & expr0 → E & ")" & E.
eval(and(A, B)) = eval(A) → EA & eval(B) → EB & and(EA, EB).
eval(or(A, B)) = eval(A) → EA & eval(B) → EB & or(EA, EB).
eval(X) = X.
and(true, true) = 'true'.
and(A, B) = 'false'.
or(false, false) = 'false'.
or(A, B) = 'true'.
scanner = scan using $:char.
scan = {" "} & ("(" | ")" | token).
token = "f" & "a" & "l" & "s" & "e" & 'false'
      | "t" & "r" & "u" & "e" & 'true'
      | "o" & "r" & 'or'
      | "a" & "n" & "d" & 'and'.