In an expression like p.x, $p$ must have a dictionary type and the field $x$ must be a field of the type of $p$.All paths through a function must have a return.(ItвЂ™s possible to encode these restrictions in the grammar, but it would be ugly). return statements may only appear in a function. break and continue statements may only appear in a loop.Sometimes names are required for arguments and sometimes not. Sometimes the number of arguments can be less or more than the number of parameters. Languages offer enormous flexibility here. Aguments must match up with parameters in terms of number, order, name, mode, etc.Sometimes both explicit import and explicit export is required. Identifiers must be used according to their scope, their access modifiers (private, protected, package, public, whitelist, blacklist, etc.) or other meta-level attributes (enumerable, configurable, writable, deletable, callable, etc.) Sometimes scope rules are obvious.Type checking also involves understanding overloading rules, the polymorphism mechanisms for the language, type inference rules, and how and when the language uses covariance, contravariance, invariance, and bivariance. (though some languages notably disallow this!), or $e$.type can be widened to $t$, e.g., byteв†’shortв†’intв†’longв†’floatв†’double.The programmer has set up an implicit conversion, or coercion, from $e$.type to $t$, or.$e$.type and $t$ have the same name, or perhaps the same structure, or.$e$.type is the exact same type as $t$, or.This may mean many things (that vary from language to language), but common rules are things like: When assigning expression $e$ to variable declared with type $t$ (or passing argument $e$ to a parameter $v$ of type $t$, or returning $e$ from a function with return type $t$), the type of $e$ must be compatible with type $t$.Overloading may be permitted to some degree.There can be multiple uniqueness buckets-in some languages, functions and non-functions are in separate namespaces.Idenitifer declarations must be unique within a scope.

Identifiers may not be used in a place where they may have not yet been initialized.Identifiers have to be declared before they are used.

In no particular order, we might see checks like: Well, that which constitutes static semantic rules varies so much from language to language, so letвЂ™s just dump a bunch of generic examples here. These notes pretty much assume you are writing a compiler for a static (or mostly-static) language. Some languages are super static, permitting almost every check to be done before execution. Dynamic languages do almost no analysis at compile time. (Recall вЂњstaticвЂќ means before execution and вЂњdynamicвЂќ means during execution.) Semantic analysis applies to some languages more than others. Note that when we say вЂњsemantic analysisвЂќ we almost always mean static semantic analaysis.

Producing a semantic graph from the AST.

Here are two to get you started: вЂњColorless green ideas sleep furiouslyвЂќ (ChomskyвЂ™s famous example), and вЂњOne gaseous solid rocks smelling the color seventeen will think yesterday.вЂќ Exercise: Come up with some English sentences that are syntactically correct but semantically nonsense.

What does semantic rules examples