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13 Cards in this Set
- Front
- Back
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Static Environment |
types of preceding bindings |
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Dynamic Environment |
values of preceding bindings |
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Syntax |
how an expression is written |
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Value |
expression that can't be simplified |
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Semantics |
How its type checked and evaluated |
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Integer Constants |
Syntax: sequence of digits Type-check: type int in any static environment Evaluation: to itself in any dynamic environment |
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Addition |
Syntax: e1+e2 where e1 and e2 are expressions Type-check: type int but inly if e1 and e2 have type int in the same static environment, else does not type-check Evaluation: evaluate e1 to v1 and e2 to v2 in the same dynamic environment and then prodce the sum of v1 and v2 |
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Variables |
Syntax: a sequence of letters, underscores, etc. Type-check: look up the variable in the current environment and use that type Eval: look up variable in current dynamic env and use that val |
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Conditionals |
Syntax: if e1 then e2 else e3 where e1, e2, and e3 are expressions Type-check: using the current static environment, a cond. type-checks only if (a) e1 has type bool and (b) e2 and e3 have the same type. The type of the whole expression is the type of e2 and e3. Eval: under dynamic env., evaluate e1. If result is true, the result of evaluating e2 under the dyn. env. is the overall result. If the result is false, the result of eval. e3 under the dynamic environment is the overall result. |
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Boolean Constants |
Syntax: either true or false Type-Check: type bool in any static environment Eval: to itself in any dynamic env. (it is a value) |
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Less than Comparison |
Syntax: e1 < e2 where e1 and e2 are expressions Type-check: type bool but only if e1 and e2 have type int in the same static env. else does not type check Eval: evaluate e1 to v1 and e2 to v2 in the same dynamic environment and then prod. true if v1 is less than v2, and false otherwise. |
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Type Check Variable Binding |
Current Static Environment |
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Evaluate a variable binding |
Current Dynamic Environment |
