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(compiler-typecase EXP (TYPE BODY ...) ... [(else BODY ...)])syntax

Evaluates EXP and executes the first clause which names a type that matches the type inferred during flow analysis as the result of EXP. The result of EXP is ignored and should be a single value. If a compiler-typecase form occurs in evaluated code, or if it occurs in compiled code but specialization is not enabled, then it must have an else clause which specifies the default code to be executed after EXP. If no else clause is given and no TYPE matches, then a compile-time error is signalled.