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GeezerVison is showing webassembly.github.io — Modules — WebAssembly 3.0 (2026-11-04) Modules¶Modules are valid when all the components they contain are valid. To verify this, most definitions are themselves classified with a suitable type. Types¶The sequence of types defined in a module is validated incrementally, yielding a sequence of defined types representing them individually. The type definition \((\href{../syntax/modules.html#syntax-type}{\mathsf{type}}~{\href{../syntax/types.html#syntax-rectype}{\mathit{rectype}}})\) is valid with the defined type sequence \({{\mathit{dt}}^\ast}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
x = {|C{.}\href{../valid/conventions.html#context}{\mathsf{types}}|}
\qquad
{{\mathit{dt}}^\ast} = {{{{\href{../valid/conventions.html#aux-roll-deftype}{\mathrm{roll}}}}_{x}^\ast}}{({\href{../syntax/types.html#syntax-rectype}{\mathit{rectype}}})}
\qquad
C \oplus \{ \href{../valid/conventions.html#context}{\mathsf{types}}~{{\mathit{dt}}^\ast} \} \href{../valid/types.html#valid-rectype}{\vdash} {\href{../syntax/types.html#syntax-rectype}{\mathit{rectype}}} : {\href{../valid/types.html#valid-subtype}{\mathsf{ok}}}{(x)}
}{
C \href{../valid/modules.html#valid-type}{\vdash} \href{../syntax/modules.html#syntax-type}{\mathsf{type}}~{\href{../syntax/types.html#syntax-rectype}{\mathit{rectype}}} : {{\mathit{dt}}^\ast}
}
\qquad
\end{array}\]
The type definition sequence \({{\href{../syntax/modules.html#syntax-type}{\mathit{type}}}^\ast}\) is valid with the defined type sequence \({{\href{../valid/conventions.html#syntax-deftype}{\mathit{deftype}}}^\ast}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
}{
C \href{../valid/modules.html#valid-types}{\vdash} \epsilon : \epsilon
}
\qquad
\frac{
C \href{../valid/modules.html#valid-type}{\vdash} {\href{../syntax/modules.html#syntax-type}{\mathit{type}}}_1 : {{\mathit{dt}}_1^\ast}
\qquad
C \oplus \{ \href{../valid/conventions.html#context}{\mathsf{types}}~{{\mathit{dt}}_1^\ast} \} \href{../valid/modules.html#valid-types}{\vdash} {{\href{../syntax/modules.html#syntax-type}{\mathit{type}}}^\ast} : {{\mathit{dt}}^\ast}
}{
C \href{../valid/modules.html#valid-types}{\vdash} {\href{../syntax/modules.html#syntax-type}{\mathit{type}}}_1~{{\href{../syntax/modules.html#syntax-type}{\mathit{type}}}^\ast} : {{\mathit{dt}}_1^\ast}~{{\mathit{dt}}^\ast}
}
\qquad
\end{array}\]
Tags¶Tags \(\href{../syntax/modules.html#syntax-tag}{\mathit{tag}}\) are classified by their tag types, which are defined types expanding to function types. The tag \((\href{../syntax/modules.html#syntax-tag}{\mathsf{tag}}~{\href{../syntax/types.html#syntax-tagtype}{\mathit{tagtype}}})\) is valid with the tag type \({\href{../syntax/types.html#syntax-tagtype}{\mathit{tagtype}}'}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C \href{../valid/types.html#valid-tagtype}{\vdash} {\href{../syntax/types.html#syntax-tagtype}{\mathit{tagtype}}} : \href{../valid/types.html#valid-tagtype}{\mathsf{ok}}
}{
C \href{../valid/modules.html#valid-tag}{\vdash} \href{../syntax/modules.html#syntax-tag}{\mathsf{tag}}~{\href{../syntax/types.html#syntax-tagtype}{\mathit{tagtype}}} : {{\href{../valid/conventions.html#aux-clostype}{\mathsf{clos}}}}_{C}({\href{../syntax/types.html#syntax-tagtype}{\mathit{tagtype}}})
}
\qquad
\end{array}\]
Globals¶Globals \({\href{../syntax/modules.html#syntax-global}{\mathit{global}}}\) are classified by global types. The global \((\href{../syntax/modules.html#syntax-global}{\mathsf{global}}~{\href{../syntax/types.html#syntax-globaltype}{\mathit{globaltype}}}~{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}})\) is valid with the global type \({\href{../syntax/types.html#syntax-globaltype}{\mathit{globaltype}}}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C \href{../valid/types.html#valid-globaltype}{\vdash} {\href{../syntax/types.html#syntax-globaltype}{\mathit{globaltype}}} : \href{../valid/types.html#valid-globaltype}{\mathsf{ok}}
\qquad
{\href{../syntax/types.html#syntax-globaltype}{\mathit{globaltype}}} = {\href{../syntax/types.html#syntax-mut}{\mathsf{mut}}^?}~t
\qquad
C \href{../valid/instructions.html#valid-constant}{\vdash} {\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : t~\href{../valid/instructions.html#valid-constant}{\mathsf{const}}
}{
C \href{../valid/modules.html#valid-global}{\vdash} \href{../syntax/modules.html#syntax-global}{\mathsf{global}}~{\href{../syntax/types.html#syntax-globaltype}{\mathit{globaltype}}}~{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : {\href{../syntax/types.html#syntax-globaltype}{\mathit{globaltype}}}
}
\qquad
\end{array}\]
Sequences of globals are handled incrementally, such that each definition has access to previous definitions. The global sequence \({{\href{../syntax/modules.html#syntax-global}{\mathit{global}}}^\ast}\) is valid with the global type sequence \({{\href{../syntax/types.html#syntax-globaltype}{\mathit{globaltype}}}^\ast}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
}{
C \href{../valid/modules.html#valid-globalseq}{\vdash} \epsilon : \epsilon
}
\qquad
\frac{
C \href{../valid/modules.html#valid-global}{\vdash} {\href{../syntax/modules.html#syntax-global}{\mathit{global}}}_1 : {\mathit{gt}}_1
\qquad
C \oplus \{ \href{../valid/conventions.html#context}{\mathsf{globals}}~{\mathit{gt}}_1 \} \href{../valid/modules.html#valid-globalseq}{\vdash} {{\href{../syntax/modules.html#syntax-global}{\mathit{global}}}^\ast} : {{\mathit{gt}}^\ast}
}{
C \href{../valid/modules.html#valid-globalseq}{\vdash} {\href{../syntax/modules.html#syntax-global}{\mathit{global}}}_1~{{\href{../syntax/modules.html#syntax-global}{\mathit{global}}}^\ast} : {\mathit{gt}}_1~{{\mathit{gt}}^\ast}
}
\qquad
\end{array}\]
Memories¶Memories \({\href{../syntax/modules.html#syntax-mem}{\mathit{mem}}}\) are classified by memory types. The memory \((\href{../syntax/modules.html#syntax-mem}{\mathsf{memory}}~{\href{../syntax/types.html#syntax-memtype}{\mathit{memtype}}})\) is valid with the memory type \({\href{../syntax/types.html#syntax-memtype}{\mathit{memtype}}}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C \href{../valid/types.html#valid-memtype}{\vdash} {\href{../syntax/types.html#syntax-memtype}{\mathit{memtype}}} : \href{../valid/types.html#valid-memtype}{\mathsf{ok}}
}{
C \href{../valid/modules.html#valid-mem}{\vdash} \href{../syntax/modules.html#syntax-mem}{\mathsf{memory}}~{\href{../syntax/types.html#syntax-memtype}{\mathit{memtype}}} : {\href{../syntax/types.html#syntax-memtype}{\mathit{memtype}}}
}
\qquad
\end{array}\]
Tables¶Tables \({\href{../syntax/modules.html#syntax-table}{\mathit{table}}}\) are classified by table types. The table \((\href{../syntax/modules.html#syntax-table}{\mathsf{table}}~{\href{../syntax/types.html#syntax-tabletype}{\mathit{tabletype}}}~{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}})\) is valid with the table type \({\href{../syntax/types.html#syntax-tabletype}{\mathit{tabletype}}}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C \href{../valid/types.html#valid-tabletype}{\vdash} {\href{../syntax/types.html#syntax-tabletype}{\mathit{tabletype}}} : \href{../valid/types.html#valid-tabletype}{\mathsf{ok}}
\qquad
{\href{../syntax/types.html#syntax-tabletype}{\mathit{tabletype}}} = {\mathit{at}}~{\mathit{lim}}~{\mathit{rt}}
\qquad
C \href{../valid/instructions.html#valid-constant}{\vdash} {\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : {\mathit{rt}}~\href{../valid/instructions.html#valid-constant}{\mathsf{const}}
}{
C \href{../valid/modules.html#valid-table}{\vdash} \href{../syntax/modules.html#syntax-table}{\mathsf{table}}~{\href{../syntax/types.html#syntax-tabletype}{\mathit{tabletype}}}~{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : {\href{../syntax/types.html#syntax-tabletype}{\mathit{tabletype}}}
}
\qquad
\end{array}\]
Functions¶Functions \({\href{../syntax/modules.html#syntax-func}{\mathit{func}}}\) are classified by defined types that expand to function types of the form \(\href{../syntax/types.html#syntax-comptype}{\mathsf{func}}~{t_1^\ast} \href{../syntax/types.html#syntax-comptype}{\rightarrow} {t_2^\ast}\). The function \((\href{../syntax/modules.html#syntax-func}{\mathsf{func}}~x~{{\href{../syntax/modules.html#syntax-local}{\mathit{local}}}^\ast}~{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}})\) is valid with the type \(C{.}\href{../valid/conventions.html#context}{\mathsf{types}}{}[x]\) if:
\[\begin{split}\begin{array}{@{}c@{}}\displaystyle
\frac{
\begin{array}{@{}c@{}}
C{.}\href{../valid/conventions.html#context}{\mathsf{types}}{}[x] \mathrel{\href{../valid/conventions.html#aux-expand-deftype}{\approx}} \href{../syntax/types.html#syntax-comptype}{\mathsf{func}}~{t_1^\ast} \href{../syntax/types.html#syntax-comptype}{\rightarrow} {t_2^\ast}
\qquad
(C \href{../valid/modules.html#valid-local}{\vdash} {\href{../syntax/modules.html#syntax-local}{\mathit{local}}} : {{\mathit{lt}}})^\ast
\\
C \oplus \{ \href{../valid/conventions.html#context}{\mathsf{locals}}~{(\href{../valid/conventions.html#syntax-init}{\mathsf{set}}~t_1)^\ast}~{{{\mathit{lt}}}^\ast},\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{labels}}~({t_2^\ast}),\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{return}}~({t_2^\ast}) \} \href{../valid/instructions.html#valid-expr}{\vdash} {\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : {t_2^\ast}
\end{array}
}{
C \href{../valid/modules.html#valid-func}{\vdash} \href{../syntax/modules.html#syntax-func}{\mathsf{func}}~x~{{\href{../syntax/modules.html#syntax-local}{\mathit{local}}}^\ast}~{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : C{.}\href{../valid/conventions.html#context}{\mathsf{types}}{}[x]
}
\qquad
\end{array}\end{split}\]
Locals¶Locals \({\href{../syntax/modules.html#syntax-local}{\mathit{local}}}\) are classified with local types. The local \((\href{../syntax/modules.html#syntax-local}{\mathsf{local}}~t)\) is valid with the local type \(({\href{../valid/conventions.html#syntax-init}{\mathit{init}}}~t)\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C \href{../valid/types.html#valid-valtype}{\vdash} t : \href{../valid/types.html#valid-valtype}{\mathsf{ok}}
\qquad
{{\href{../exec/runtime.html#aux-default}{\mathrm{default}}}}_{t} \neq \epsilon
}{
C \href{../valid/modules.html#valid-local}{\vdash} \href{../syntax/modules.html#syntax-local}{\mathsf{local}}~t : \href{../valid/conventions.html#syntax-init}{\mathsf{set}}~t
}
\qquad
\frac{
C \href{../valid/types.html#valid-valtype}{\vdash} t : \href{../valid/types.html#valid-valtype}{\mathsf{ok}}
\qquad
{{\href{../exec/runtime.html#aux-default}{\mathrm{default}}}}_{t} = \epsilon
}{
C \href{../valid/modules.html#valid-local}{\vdash} \href{../syntax/modules.html#syntax-local}{\mathsf{local}}~t : \href{../valid/conventions.html#syntax-init}{\mathsf{unset}}~t
}
\qquad
\end{array}\]
Note For cases where both rules are applicable, the former yields the more permissable type. Data Segments¶Data segments \({\href{../syntax/modules.html#syntax-data}{\mathit{data}}}\) are classified by the singleton data type, which merely expresses well-formedness. The memory segment \((\href{../syntax/modules.html#syntax-data}{\mathsf{data}}~{b^\ast}~{\href{../syntax/modules.html#syntax-datamode}{\mathit{datamode}}})\) is valid if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C \href{../valid/modules.html#valid-datamode}{\vdash} {\href{../syntax/modules.html#syntax-datamode}{\mathit{datamode}}} : \href{../valid/modules.html#valid-data}{\mathsf{ok}}
}{
C \href{../valid/modules.html#valid-data}{\vdash} \href{../syntax/modules.html#syntax-data}{\mathsf{data}}~{b^\ast}~{\href{../syntax/modules.html#syntax-datamode}{\mathit{datamode}}} : \href{../valid/modules.html#valid-data}{\mathsf{ok}}
}
\qquad
\end{array}\]
The data mode \({\href{../syntax/modules.html#syntax-datamode}{\mathit{datamode}}}\) is valid if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
}{
C \href{../valid/modules.html#valid-datamode}{\vdash} \href{../syntax/modules.html#syntax-datamode}{\mathsf{passive}} : \href{../valid/modules.html#valid-data}{\mathsf{ok}}
}
\qquad
\frac{
C{.}\href{../valid/conventions.html#context}{\mathsf{mems}}{}[x] = {\mathit{at}}~{\mathit{lim}}~\href{../syntax/types.html#syntax-memtype}{\mathsf{page}}
\qquad
C \href{../valid/instructions.html#valid-constant}{\vdash} {\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : {\mathit{at}}~\href{../valid/instructions.html#valid-constant}{\mathsf{const}}
}{
C \href{../valid/modules.html#valid-datamode}{\vdash} \href{../syntax/modules.html#syntax-datamode}{\mathsf{active}}~x~{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : \href{../valid/modules.html#valid-data}{\mathsf{ok}}
}
\qquad
\end{array}\]
Element Segments¶Element segments \({\href{../syntax/modules.html#syntax-elem}{\mathit{elem}}}\) are classified by their element type. The table segment \((\href{../syntax/modules.html#syntax-elem}{\mathsf{elem}}~{\href{../syntax/types.html#syntax-elemtype}{\mathit{elemtype}}}~{{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}}^\ast}~{\href{../syntax/modules.html#syntax-elemmode}{\mathit{elemmode}}})\) is valid with the element type \({\href{../syntax/types.html#syntax-elemtype}{\mathit{elemtype}}}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C \href{../valid/types.html#valid-reftype}{\vdash} {\href{../syntax/types.html#syntax-elemtype}{\mathit{elemtype}}} : \href{../valid/types.html#valid-reftype}{\mathsf{ok}}
\qquad
(C \href{../valid/instructions.html#valid-constant}{\vdash} {\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : {\href{../syntax/types.html#syntax-elemtype}{\mathit{elemtype}}}~\href{../valid/instructions.html#valid-constant}{\mathsf{const}})^\ast
\qquad
C \href{../valid/modules.html#valid-elemmode}{\vdash} {\href{../syntax/modules.html#syntax-elemmode}{\mathit{elemmode}}} : {\href{../syntax/types.html#syntax-elemtype}{\mathit{elemtype}}}
}{
C \href{../valid/modules.html#valid-elem}{\vdash} \href{../syntax/modules.html#syntax-elem}{\mathsf{elem}}~{\href{../syntax/types.html#syntax-elemtype}{\mathit{elemtype}}}~{{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}}^\ast}~{\href{../syntax/modules.html#syntax-elemmode}{\mathit{elemmode}}} : {\href{../syntax/types.html#syntax-elemtype}{\mathit{elemtype}}}
}
\qquad
\end{array}\]
The element mode \({\href{../syntax/modules.html#syntax-elemmode}{\mathit{elemmode}}}\) is valid with the element type \({\mathit{rt}}\) if:
\[\begin{split}\begin{array}{@{}c@{}}\displaystyle
\frac{
}{
C \href{../valid/modules.html#valid-elemmode}{\vdash} \href{../syntax/modules.html#syntax-elemmode}{\mathsf{passive}} : {\mathit{rt}}
}
\qquad
\frac{
}{
C \href{../valid/modules.html#valid-elemmode}{\vdash} \href{../syntax/modules.html#syntax-elemmode}{\mathsf{declare}} : {\mathit{rt}}
}
\\[3ex]\displaystyle
\frac{
C{.}\href{../valid/conventions.html#context}{\mathsf{tables}}{}[x] = {\mathit{at}}~{\mathit{lim}}~{\mathit{rt}'}
\qquad
C \href{../valid/matching.html#match-reftype}{\vdash} {\mathit{rt}} \href{../valid/matching.html#match-reftype}{\leq} {\mathit{rt}'}
\qquad
C \href{../valid/instructions.html#valid-constant}{\vdash} {\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : {\mathit{at}}~\href{../valid/instructions.html#valid-constant}{\mathsf{const}}
}{
C \href{../valid/modules.html#valid-elemmode}{\vdash} \href{../syntax/modules.html#syntax-elemmode}{\mathsf{active}}~x~{\href{../syntax/instructions.html#syntax-expr}{\mathit{expr}}} : {\mathit{rt}}
}
\qquad
\end{array}\end{split}\]
Start Function¶The start function \((\href{../syntax/modules.html#syntax-start}{\mathsf{start}}~x)\) is valid if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C{.}\href{../valid/conventions.html#context}{\mathsf{funcs}}{}[x] \mathrel{\href{../valid/conventions.html#aux-expand-deftype}{\approx}} \href{../syntax/types.html#syntax-comptype}{\mathsf{func}}~\epsilon \href{../syntax/types.html#syntax-comptype}{\rightarrow} \epsilon
}{
C \href{../valid/modules.html#valid-start}{\vdash} \href{../syntax/modules.html#syntax-start}{\mathsf{start}}~x : \href{../valid/modules.html#valid-start}{\mathsf{ok}}
}
\qquad
\end{array}\]
Imports¶Imports \({\href{../syntax/modules.html#syntax-import}{\mathit{import}}}\) are classified by external types. The import \((\href{../syntax/modules.html#syntax-import}{\mathsf{import}}~{\href{../syntax/values.html#syntax-name}{\mathit{name}}}_1~{\href{../syntax/values.html#syntax-name}{\mathit{name}}}_2~{\mathit{xt}})\) is valid with the external type \({\href{../syntax/types.html#syntax-externtype}{\mathit{externtype}}}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C \href{../valid/types.html#valid-externtype}{\vdash} {\mathit{xt}} : \href{../valid/types.html#valid-externtype}{\mathsf{ok}}
}{
C \href{../valid/modules.html#valid-import}{\vdash} \href{../syntax/modules.html#syntax-import}{\mathsf{import}}~{\href{../syntax/values.html#syntax-name}{\mathit{name}}}_1~{\href{../syntax/values.html#syntax-name}{\mathit{name}}}_2~{\mathit{xt}} : {{\href{../valid/conventions.html#aux-clostype}{\mathsf{clos}}}}_{C}({\mathit{xt}})
}
\qquad
\end{array}\]
Exports¶Exports \({\href{../syntax/modules.html#syntax-export}{\mathit{export}}}\) are classified by their external type. The export \((\href{../syntax/modules.html#syntax-export}{\mathsf{export}}~{\href{../syntax/values.html#syntax-name}{\mathit{name}}}~{\href{../syntax/modules.html#syntax-externidx}{\mathit{externidx}}})\) is valid with the name \({\href{../syntax/values.html#syntax-name}{\mathit{name}}}\) and the external type \({\mathit{xt}}\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C \href{../valid/modules.html#valid-externidx}{\vdash} {\href{../syntax/modules.html#syntax-externidx}{\mathit{externidx}}} : {\mathit{xt}}
}{
C \href{../valid/modules.html#valid-export}{\vdash} \href{../syntax/modules.html#syntax-export}{\mathsf{export}}~{\href{../syntax/values.html#syntax-name}{\mathit{name}}}~{\href{../syntax/modules.html#syntax-externidx}{\mathit{externidx}}} : {\href{../syntax/values.html#syntax-name}{\mathit{name}}}~{\mathit{xt}}
}
\qquad
\end{array}\]
\(\href{../syntax/modules.html#syntax-externidx}{\mathsf{tag}}~x\)¶The external index \((\href{../syntax/modules.html#syntax-externidx}{\mathsf{tag}}~x)\) is valid with the external type \((\href{../syntax/types.html#syntax-externtype}{\mathsf{tag}}~{\mathit{jt}})\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C{.}\href{../valid/conventions.html#context}{\mathsf{tags}}{}[x] = {\mathit{jt}}
}{
C \href{../valid/modules.html#valid-externidx}{\vdash} \href{../syntax/modules.html#syntax-externidx}{\mathsf{tag}}~x : \href{../syntax/types.html#syntax-externtype}{\mathsf{tag}}~{\mathit{jt}}
}
\qquad
\end{array}\]
\(\href{../syntax/modules.html#syntax-externidx}{\mathsf{global}}~x\)¶The external index \((\href{../syntax/modules.html#syntax-externidx}{\mathsf{global}}~x)\) is valid with the external type \((\href{../syntax/types.html#syntax-externtype}{\mathsf{global}}~{\mathit{gt}})\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C{.}\href{../valid/conventions.html#context}{\mathsf{globals}}{}[x] = {\mathit{gt}}
}{
C \href{../valid/modules.html#valid-externidx}{\vdash} \href{../syntax/modules.html#syntax-externidx}{\mathsf{global}}~x : \href{../syntax/types.html#syntax-externtype}{\mathsf{global}}~{\mathit{gt}}
}
\qquad
\end{array}\]
\(\href{../syntax/modules.html#syntax-externidx}{\mathsf{memory}}~x\)¶The external index \((\href{../syntax/modules.html#syntax-externidx}{\mathsf{memory}}~x)\) is valid with the external type \((\href{../syntax/types.html#syntax-externtype}{\mathsf{mem}}~{\mathit{mt}})\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C{.}\href{../valid/conventions.html#context}{\mathsf{mems}}{}[x] = {\mathit{mt}}
}{
C \href{../valid/modules.html#valid-externidx}{\vdash} \href{../syntax/modules.html#syntax-externidx}{\mathsf{memory}}~x : \href{../syntax/types.html#syntax-externtype}{\mathsf{mem}}~{\mathit{mt}}
}
\qquad
\end{array}\]
\(\href{../syntax/modules.html#syntax-externidx}{\mathsf{table}}~x\)¶The external index \((\href{../syntax/modules.html#syntax-externidx}{\mathsf{table}}~x)\) is valid with the external type \((\href{../syntax/types.html#syntax-externtype}{\mathsf{table}}~{\mathit{tt}})\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C{.}\href{../valid/conventions.html#context}{\mathsf{tables}}{}[x] = {\mathit{tt}}
}{
C \href{../valid/modules.html#valid-externidx}{\vdash} \href{../syntax/modules.html#syntax-externidx}{\mathsf{table}}~x : \href{../syntax/types.html#syntax-externtype}{\mathsf{table}}~{\mathit{tt}}
}
\qquad
\end{array}\]
\(\href{../syntax/modules.html#syntax-externidx}{\mathsf{func}}~x\)¶The external index \((\href{../syntax/modules.html#syntax-externidx}{\mathsf{func}}~x)\) is valid with the external type \((\href{../syntax/types.html#syntax-externtype}{\mathsf{func}}~{\mathit{dt}})\) if:
\[\begin{array}{@{}c@{}}\displaystyle
\frac{
C{.}\href{../valid/conventions.html#context}{\mathsf{funcs}}{}[x] = {\mathit{dt}}
}{
C \href{../valid/modules.html#valid-externidx}{\vdash} \href{../syntax/modules.html#syntax-externidx}{\mathsf{func}}~x : \href{../syntax/types.html#syntax-externtype}{\mathsf{func}}~{\mathit{dt}}
}
\qquad
\end{array}\]
Modules¶Modules are classified by their mapping from the external types of their imports to those of their exports. A module is entirely closed, that is, its components can only refer to definitions that appear in the module itself. Consequently, no initial context is required. Instead, the context \(C\) for validation of the module’s content is constructed from the definitions in the module. The module \((\href{../syntax/modules.html#syntax-module}{\mathsf{module}}~{{\href{../syntax/modules.html#syntax-type}{\mathit{type}}}^\ast}~{{\href{../syntax/modules.html#syntax-import}{\mathit{import}}}^\ast}~{{\href{../syntax/modules.html#syntax-tag}{\mathit{tag}}}^\ast}~{{\href{../syntax/modules.html#syntax-global}{\mathit{global}}}^\ast}~{{\href{../syntax/modules.html#syntax-mem}{\mathit{mem}}}^\ast}~{{\href{../syntax/modules.html#syntax-table}{\mathit{table}}}^\ast}~{{\href{../syntax/modules.html#syntax-func}{\mathit{func}}}^\ast}~{{\href{../syntax/modules.html#syntax-data}{\mathit{data}}}^\ast}~{{\href{../syntax/modules.html#syntax-elem}{\mathit{elem}}}^\ast}~{{\href{../syntax/modules.html#syntax-start}{\mathit{start}}}^?}~{{\href{../syntax/modules.html#syntax-export}{\mathit{export}}}^\ast})\) is valid with the module type \({\href{../valid/modules.html#syntax-moduletype}{\mathit{moduletype}}}\) if:
\[\begin{split}\begin{array}{@{}c@{}}\displaystyle
\frac{
\begin{array}{@{}c@{}}
\{ \} \href{../valid/modules.html#valid-types}{\vdash} {{\href{../syntax/modules.html#syntax-type}{\mathit{type}}}^\ast} : {{\mathit{dt}'}^\ast}
\qquad
(\{ \href{../valid/conventions.html#context}{\mathsf{types}}~{{\mathit{dt}'}^\ast} \} \href{../valid/modules.html#valid-import}{\vdash} {\href{../syntax/modules.html#syntax-import}{\mathit{import}}} : {\mathit{xt}}_{\mathsf{i}})^\ast
\\
({C'} \href{../valid/modules.html#valid-tag}{\vdash} {\href{../syntax/modules.html#syntax-tag}{\mathit{tag}}} : {\mathit{jt}})^\ast
\qquad
{C'} \href{../valid/modules.html#valid-globalseq}{\vdash} {{\href{../syntax/modules.html#syntax-global}{\mathit{global}}}^\ast} : {{\mathit{gt}}^\ast}
\qquad
({C'} \href{../valid/modules.html#valid-mem}{\vdash} {\href{../syntax/modules.html#syntax-mem}{\mathit{mem}}} : {\mathit{mt}})^\ast
\qquad
({C'} \href{../valid/modules.html#valid-table}{\vdash} {\href{../syntax/modules.html#syntax-table}{\mathit{table}}} : {\mathit{tt}})^\ast
\qquad
(C \href{../valid/modules.html#valid-func}{\vdash} {\href{../syntax/modules.html#syntax-func}{\mathit{func}}} : {\mathit{dt}})^\ast
\\
(C \href{../valid/modules.html#valid-data}{\vdash} {\href{../syntax/modules.html#syntax-data}{\mathit{data}}} : {\mathit{ok}})^\ast
\qquad
(C \href{../valid/modules.html#valid-elem}{\vdash} {\href{../syntax/modules.html#syntax-elem}{\mathit{elem}}} : {\mathit{rt}})^\ast
\qquad
(C \href{../valid/modules.html#valid-start}{\vdash} {\href{../syntax/modules.html#syntax-start}{\mathit{start}}} : \href{../valid/modules.html#valid-start}{\mathsf{ok}})^?
\qquad
(C \href{../valid/modules.html#valid-export}{\vdash} {\href{../syntax/modules.html#syntax-export}{\mathit{export}}} : {\mathit{nm}}~{\mathit{xt}}_{\mathsf{e}})^\ast
\qquad
{{\mathit{nm}}^\ast}~{\mathrm{disjoint}}
\\
C = {C'} \oplus \{ \href{../valid/conventions.html#context}{\mathsf{tags}}~{{\mathit{jt}}_{\mathsf{i}}^\ast}~{{\mathit{jt}}^\ast},\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{globals}}~{{\mathit{gt}}^\ast},\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{mems}}~{{\mathit{mt}}_{\mathsf{i}}^\ast}~{{\mathit{mt}}^\ast},\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{tables}}~{{\mathit{tt}}_{\mathsf{i}}^\ast}~{{\mathit{tt}}^\ast},\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{datas}}~{{\mathit{ok}}^\ast},\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{elems}}~{{\mathit{rt}}^\ast} \}
\\
{C'} = \{ \href{../valid/conventions.html#context}{\mathsf{types}}~{{\mathit{dt}'}^\ast},\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{globals}}~{{\mathit{gt}}_{\mathsf{i}}^\ast},\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{funcs}}~{{\mathit{dt}}_{\mathsf{i}}^\ast}~{{\mathit{dt}}^\ast},\;\allowbreak \href{../valid/conventions.html#context}{\mathsf{refs}}~{x^\ast} \}
\qquad
{x^\ast} = {\href{../syntax/modules.html#syntax-funcidx}{\mathrm{funcidx}}}({{\href{../syntax/modules.html#syntax-global}{\mathit{global}}}^\ast}~{{\href{../syntax/modules.html#syntax-mem}{\mathit{mem}}}^\ast}~{{\href{../syntax/modules.html#syntax-table}{\mathit{table}}}^\ast}~{{\href{../syntax/modules.html#syntax-elem}{\mathit{elem}}}^\ast}~{{\href{../syntax/modules.html#syntax-export}{\mathit{export}}}^\ast})
\\
{{\mathit{jt}}_{\mathsf{i}}^\ast} = {\href{../syntax/types.html#syntax-externtype}{\mathrm{tags}}}({{\mathit{xt}}_{\mathsf{i}}^\ast})
\qquad
{{\mathit{gt}}_{\mathsf{i}}^\ast} = {\href{../syntax/types.html#syntax-externtype}{\mathrm{globals}}}({{\mathit{xt}}_{\mathsf{i}}^\ast})
\qquad
{{\mathit{mt}}_{\mathsf{i}}^\ast} = {\href{../syntax/types.html#syntax-externtype}{\mathrm{mems}}}({{\mathit{xt}}_{\mathsf{i}}^\ast})
\qquad
{{\mathit{tt}}_{\mathsf{i}}^\ast} = {\href{../syntax/types.html#syntax-externtype}{\mathrm{tables}}}({{\mathit{xt}}_{\mathsf{i}}^\ast})
\qquad
{{\mathit{dt}}_{\mathsf{i}}^\ast} = {\href{../syntax/types.html#syntax-externtype}{\mathrm{funcs}}}({{\mathit{xt}}_{\mathsf{i}}^\ast})
\end{array}
}{
{\href{../valid/modules.html#valid-module}{\vdash}}\, \href{../syntax/modules.html#syntax-module}{\mathsf{module}}~{{\href{../syntax/modules.html#syntax-type}{\mathit{type}}}^\ast}~{{\href{../syntax/modules.html#syntax-import}{\mathit{import}}}^\ast}~{{\href{../syntax/modules.html#syntax-tag}{\mathit{tag}}}^\ast}~{{\href{../syntax/modules.html#syntax-global}{\mathit{global}}}^\ast}~{{\href{../syntax/modules.html#syntax-mem}{\mathit{mem}}}^\ast}~{{\href{../syntax/modules.html#syntax-table}{\mathit{table}}}^\ast}~{{\href{../syntax/modules.html#syntax-func}{\mathit{func}}}^\ast}~{{\href{../syntax/modules.html#syntax-data}{\mathit{data}}}^\ast}~{{\href{../syntax/modules.html#syntax-elem}{\mathit{elem}}}^\ast}~{{\href{../syntax/modules.html#syntax-start}{\mathit{start}}}^?}~{{\href{../syntax/modules.html#syntax-export}{\mathit{export}}}^\ast} : {{\href{../valid/conventions.html#aux-clostype}{\mathsf{clos}}}}_{C}({{\mathit{xt}}_{\mathsf{i}}^\ast} \mathrel{\href{../valid/modules.html#syntax-moduletype}{\rightarrow}} {{\mathit{xt}}_{\mathsf{e}}^\ast})
}
\qquad
\end{array}\end{split}\]
Note All functions in a module are mutually recursive. Consequently, the definition of the context \(C\) in this rule is recursive: it depends on the outcome of validation of the function, table, memory, and global definitions contained in the module, which itself depends on \(C\). However, this recursion is just a specification device. All types needed to construct \(C\) can easily be determined from a simple pre-pass over the module that does not perform any actual validation. Globals, however, are not recursive but evaluated sequentially, such that each constant expressions only has access to imported or previously defined globals.
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