Continue¶

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description¶

Continue[]

proceeds to the next iteration of the nearest enclosing Do, For, or While loop.

Continue[]

skips the remainder of the current loop body.

Continue[]

takes effect as soon as it is evaluated.

Notes

Continue has attribute Protected.

Examples (5)¶

Every input below was run against the current Mathilda build and its output recorded.

Basic examples (2)¶

In[1]:= r = 0; Do[If[EvenQ[i], Continue[]]; r += i, {i, 10}]; r
Out[1]= 25

In[2]:= r = 0; For[i = 1, i <= 10, i++, If[EvenQ[i], Continue[]]; r += i]; r
Out[2]= 25

Applications (3)¶

Skip the even i and sum the odd ones

In[3]:= r = 0; Do[If[EvenQ[i], Continue[]]; r += i, {i, 10}]; r
Out[3]= 25

In For, Continue still runs the increment step

In[4]:= r = 0; For[i = 1, i <= 6, i++, If[i == 3, Continue[]]; r += i]; r
Out[4]= 18

Inert outside any loop

In[5]:= Continue[]
Out[5]= Hold[Continue[]]

Implementation notes¶

Algorithm. Continue[] is a zero-argument flow-control marker, Protected with no Hold attributes. builtin_continue validates arity only — a non-zero argument count emits Continue::argx through builtin_arg_error — and otherwise returns NULL, so the raw Continue[] node stands as the marker. Like Break, it is a head-detected marker (Mechanism B), recognised by the loop builtins through iter_flow_classify (interned SYM_Continue) and not short-circuited in the argument-evaluation loop, so it only takes effect at a loop boundary.

Data structures. None; a bare unevaluated node matched by head.

Complexity / limits. Continue[] skips the remainder of the current body of the innermost Do/For/While and advances to the next iteration: in Do it advances the iterator and re-tests (the arithmetic-progression form must still step its running value on ITER_FLOW_CONTINUE, else the loop would spin), in For it evaluates the increment step and re-tests, and in While it re-evaluates the test. A Continue[] that reaches top level is reported with Continue::nofwd by eval_report_uncaught_break_continue and rewritten to the inert Hold[Continue[]].

Has attribute Protected.
Takes effect as soon as it is evaluated. In Do it advances the iterator and re-tests; in For it evaluates the increment step then re-tests; in While it re-evaluates the test.
Outside any loop, Continue[] emits the message Continue::nofwd and returns Hold[Continue[]].

Attributes: Protected.

References¶

See also: Do, For, While

Source: src/iter.c
Specification: docs/spec/builtins/control-flow.md
Tests: tests/test_iter.c
Tests: tests/test_return.c

Notes & additional examples¶

Notes¶

Continue[] abandons the rest of the current loop body and moves to the next iteration of the innermost Do, For or While. What "next iteration" means differs by loop: Do advances its iterator and re-tests, For evaluates its increment step and re-tests, and While re-evaluates its test.

Like Break, it is a head-detected marker and takes effect only at a loop boundary. Outside any loop it prints Continue::nofwd and returns the inert Hold[Continue[]].